Fragment

Fragment

Fragment的产生

什么是Fragment

Fragment的使用方法

MainActivity.java

package a.b.c.fragmentbase;

import android.os.Bundle;

import androidx.activity.EdgeToEdge;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:layout_height="match_parent"
    android:layout_width="match_parent"
    android:orientation="vertical"
    xmlns:android="http://schemas.android.com/apk/res/android">
    
    <fragment
              android:name="a.b.c.fragmentbase.BlankFragment1"
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:id="@id/fragment1"/>
</LinearLayout>

BlankFragment1.java

package a.b.c.fragmentbase;

import android.os.Bundle;

import androidx.fragment.app.Fragment;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;

public class BlankFragment1 extends Fragment{
    private View root;
    private TextView textView;
    private Button button;
    
    @Override
    public void onCreate(Bundle saveInstanceState){
        super.onCreate(savedInstanceState);
    }
    @Override
    public void onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
        if(root == null){
            root = inflater.inflate(R.layout.fragment_blank1, container, false);
        }
        textView = root.findViewById(R.id.btn);
        button.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View view){
                textView.setText("Yes, I am, and you?");
            }
        });
        return root;
    }
}

fragment_blank1.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:layout_height="match_parent"
    android:layout_width="match_parent"
    android:orientation="vertical"
    xmlns:android="http://schemas.android.com/apk/res/android">
    <TextView
        android:layout_width="match_parent"
        android:layout_height="40dp"
        android:text="@string/hello_blank_fragment"
        android:id="@+id/textview"/>

    <Button
        android:layout_width="match_parent"
        android:layout_height="40dp"
        android:id="@+id/btn"
        android:text="How are you?"/>
</LinearLayout>

在activity中简单的添加两个fragment

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:layout_height="match_parent"
    android:layout_width="match_parent"
    android:orientation="vertical"
    xmlns:android="http://schemas.android.com/apk/res/android">

    <fragment
        android:name="a.b.c.fragmentbase.BlankFragment1"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:id="@+id/fragment1"/>

    <fragment
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:name="a.b.c.fragmentbase.BlankFragment2"
        android:layout_weight="1"
        android:id="@+id/fragment2"/>

</LinearLayout>

Fragment的产生

动态添加Fragment

JDK17以上版本无法使用switch的解决方法：

MainActivity.java

package a.b.c.fragmentmangers;

import android.os.Bundle;
import android.view.View;
import android.view.WindowManager;
import android.widget.Button;
import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentTransaction;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    private Button btn;
    private Button btn2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btn = findViewById(R.id.btn); // 使用正确的 ID
        btn.setOnClickListener(this);
        btn2 = findViewById(R.id.btn_2); // 处理其他按钮
        btn2.setOnClickListener(this);
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.btn:
                replaceFragment(new BlankFragment1());
                break;

            case R.id.btn_2:
                replaceFragment(new ItemFragment());
                break;
        }
    }

    private void replaceFragment(Fragment fragment) {
        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction transaction = fragmentManager.beginTransaction();
        transaction.replace(R.id.framelayout,fragment);
        transaction.addToBackStack(null);//添加到同一个栈中，这样用户可以按返回键时回到之前的状态。
        /*replace(int containerViewId, Fragment fragment) 是 FragmentTransaction 类中的一个方法，用于将一个 Fragment 替换到指定的容器中。

containerViewId: 这是一个 int 类型的参数，表示容器的资源 ID。这个容器通常是一个 FrameLayout 或者其他可以承载 Fragment 的视图组件。你在布局文件中定义这个容器时会为它分配一个 ID（在这个例子中是 R.id.framelayout）。

fragment: 这是你希望替换到容器中的新的 Fragment 实例。这个 Fragment 对象是你要显示的新内容或界面。*/
        transaction.commit();
    }
}

BlankFragment1

package a.b.c.fragmentmangers;

import android.os.Bundle;

import androidx.fragment.app.Fragment;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

/**
 * A simple {@link Fragment} subclass.
 * Use the {@link BlankFragment1#newInstance} factory method to
 * create an instance of this fragment.
 */
public class BlankFragment1 extends Fragment {

    // TODO: Rename parameter arguments, choose names that match
    // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";

    // TODO: Rename and change types of parameters
    private String mParam1;
    private String mParam2;

    public BlankFragment1() {
        // Required empty public constructor
    }

    /**
     * Use this factory method to create a new instance of
     * this fragment using the provided parameters.
     *
     * @param param1 Parameter 1.
     * @param param2 Parameter 2.
     * @return A new instance of fragment BlankFragment1.
     */
    // TODO: Rename and change types and number of parameters
    public static BlankFragment1 newInstance(String param1, String param2) {
        BlankFragment1 fragment = new BlankFragment1();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_blank1, container, false);
    }
}

ItemFragment

package a.b.c.fragmentmangers;

import android.content.Context;
import android.os.Bundle;

import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.GridLayoutManager;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import a.b.c.fragmentmangers.placeholder.PlaceholderContent;

/**
 * A fragment representing a list of Items.
 */
public class ItemFragment extends Fragment {

    // TODO: Customize parameter argument names
    private static final String ARG_COLUMN_COUNT = "column-count";
    // TODO: Customize parameters
    private int mColumnCount = 1;

    /**
     * Mandatory empty constructor for the fragment manager to instantiate the
     * fragment (e.g. upon screen orientation changes).
     */
    public ItemFragment() {
    }

    // TODO: Customize parameter initialization
    @SuppressWarnings("unused")
    public static ItemFragment newInstance(int columnCount) {
        ItemFragment fragment = new ItemFragment();
        Bundle args = new Bundle();
        args.putInt(ARG_COLUMN_COUNT, columnCount);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        if (getArguments() != null) {
            mColumnCount = getArguments().getInt(ARG_COLUMN_COUNT);
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_item_list, container, false);

        // Set the adapter
        if (view instanceof RecyclerView) {
            Context context = view.getContext();
            RecyclerView recyclerView = (RecyclerView) view;
            if (mColumnCount <= 1) {
                recyclerView.setLayoutManager(new LinearLayoutManager(context));
            } else {
                recyclerView.setLayoutManager(new GridLayoutManager(context, mColumnCount));
            }
            recyclerView.setAdapter(new MyItemRecyclerViewAdapter(PlaceholderContent.ITEMS));
        }
        return view;
    }
}

MyItemRecyclerViewAdapter.java

package a.b.c.fragmentmangers;

import androidx.recyclerview.widget.RecyclerView;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import a.b.c.fragmentmangers.placeholder.PlaceholderContent.PlaceholderItem;
import a.b.c.fragmentmangers.databinding.FragmentItemBinding;

import java.util.List;

/**
 * {@link RecyclerView.Adapter} that can display a {@link PlaceholderItem}.
 * TODO: Replace the implementation with code for your data type.
 */
public class MyItemRecyclerViewAdapter extends RecyclerView.Adapter<MyItemRecyclerViewAdapter.ViewHolder> {

    private final List<PlaceholderItem> mValues;

    public MyItemRecyclerViewAdapter(List<PlaceholderItem> items) {
        mValues = items;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

        return new ViewHolder(FragmentItemBinding.inflate(LayoutInflater.from(parent.getContext()), parent, false));

    }

    @Override
    public void onBindViewHolder(final ViewHolder holder, int position) {
        holder.mItem = mValues.get(position);
        holder.mIdView.setText(mValues.get(position).id);
        holder.mContentView.setText(mValues.get(position).content);
    }

    @Override
    public int getItemCount() {
        return mValues.size();
    }

    public class ViewHolder extends RecyclerView.ViewHolder {
        public final TextView mIdView;
        public final TextView mContentView;
        public PlaceholderItem mItem;

        public ViewHolder(FragmentItemBinding binding) {
            super(binding.getRoot());
            mIdView = binding.itemNumber;
            mContentView = binding.content;
        }

        @Override
        public String toString() {
            return super.toString() + " '" + mContentView.getText() + "'";
        }
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:layout_height="match_parent"
    android:orientation="vertical"
    android:layout_width="match_parent"
    xmlns:android="http://schemas.android.com/apk/res/android">
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/btn"
        android:text="change"/>

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/btn_2"
        android:text="replace"/>

    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/framelayout"
        android:background="#00BCD4"/>

</LinearLayout>

fragment_blank1.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".BlankFragment1">

    <!-- TODO: Update blank fragment layout -->
    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="@string/hello_blank_fragment" />

</FrameLayout>

fragment_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="horizontal">

    <TextView
        android:id="@+id/item_number"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="@dimen/text_margin"
        android:textAppearance="?attr/textAppearanceListItem" />

    <TextView
        android:id="@+id/content"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="@dimen/text_margin"
        android:textAppearance="?attr/textAppearanceListItem" />
</LinearLayout>

fragment_item_list.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.recyclerview.widget.RecyclerView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/list"
    android:name="a.b.c.fragmentmangers.ItemFragment"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_marginLeft="16dp"
    android:layout_marginRight="16dp"
    app:layoutManager="LinearLayoutManager"
    tools:context=".ItemFragment"
    tools:listitem="@layout/fragment_item" />

Activity与Fragment通信

使用Bundle

MainActivity.java

@Override
public void onClick(View view){
    switch(view.getId()){
        case R.id.btn:
            Bundle bundle = new Bundle();
            bundle.putString("lele","lele");
            BlankFragment1 bf = new BlankFragment1();
            bf.setArguments(bundle);
            replaceFragment(bf);
            break;
    }
}

BlankFragment1.java

@Override
public void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    Bundle bundle = this.getArguments();
    String string = bundle.getString("lele");
    Log.i("lele",string);
    if(getArguments()!=null){
        mParam1 = getArguments().getString(ARG_PARAM1);
        mParam2 = getArguments().getString(ARG_PAEAM2);
    }
}

fragment动态添加与管理的总结

Fragment与activity通信的接口方案

• 原生方案：Bundle
• Java语言中类与类之间通信常用方案：接口

MainActivity.java

package a.b.c.fragmentmangers;

import android.os.Bundle;
import android.view.View;
import android.view.WindowManager;
import android.widget.Button;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentTransaction;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{
    private Button btn;
    private Button btn2;
    @Override
    protected void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btn = findViewById(R.id.btn_2);
        btn2.setOnClickListener(this);
    }
    @Override
    public void onClick(View view){
        switch(view.getId()){
            case R.id.btn:
                Bundle bundle = new Bundle();
                bundle.putString("lele","lele");
                BlankFragment1(bundle);
                bf.setFragmentCallback(new IFragmentCallback(){
                    @Override
                    public void sendMsgToActivity(String msg){
                        Toast.makeText(MainActivity.this,msg,Toast.LENGTH_SHORT).show();
                    }
                    @Override
                    public String getMsgFromActivity(String msg){
                        return "hello, I am from MainActivity";
                    }
                                     
                });
                replaceFragment(bf);
                break;
                
            case R.id.btn_2:
                replaceFragment(new ItemFragment());
                break;
        }
    }
    private void replaceFragment(Fragment fragment){
        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction transaction = fragmentManager.beginTransaction();
        transaction.replace(R.id.framelayout,fragment);
        transaction.addToBackStack(null);
    }
}

IFragmentCallback.java

package a.b.c.fragmentmangers;
public interface IFragmentCallback{
    void sendMsgToActivity(String string);
    String getMsgFromActivity(String msg);
}

BlankFragment1.java

package a.b.c.fragmentmangers;

import android.os.Bundle;

import androidx.fragment.app.Fragment;

import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.Toast;

/**
 * A simple {@link Fragment} subclass.
 * Use the {@link BlankFragment1#newInstance} factory method to
 * create an instance of this fragment.
 */
public class BlankFragment1 extends Fragment {

    // TODO: Rename parameter arguments, choose names that match
    // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";

    // TODO: Rename and change types of parameters
    private String mParam1;
    private String mParam2;
    private View rootview;

    public BlankFragment1() {
        // Required empty public constructor
    }

    /**
     * Use this factory method to create a new instance of
     * this fragment using the provided parameters.
     *
     * @param param1 Parameter 1.
     * @param param2 Parameter 2.
     * @return A new instance of fragment BlankFragment1.
     */
    // TODO: Rename and change types and number of parameters
    public static BlankFragment1 newInstance(String param1, String param2) {
        BlankFragment1 fragment = new BlankFragment1();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Bundle bundle = this.getArguments();
        String string = bundle.getString("lele");
        Log.i("lele",string);
        if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        if(rootview == null){
            rootview = inflater.inflate(R.layout.fragment_blank1, container, false);
        }
        Button btn = rootview.findViewById(R.id.btn_3);
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                //fragmentCallback.sendMsgToActivity("hello, I`m from Fragment");
                String message = fragmentCallback.getMsgFromActivity("null");
                Toast.makeText(BlankFragment1.this.getContext(),message,Toast.LENGTH_SHORT).show();
            }
        });


        return rootview;
    }

    private IFragmentCallback fragmentCallback;
    public void setFragmentCallback(IFragmentCallback callback){
        fragmentCallback = callback;
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:layout_height="match_parent"
    android:orientation="vertical"
    android:layout_width="match_parent"
    xmlns:android="http://schemas.android.com/apk/res/android">
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/btn"
        android:text="change"/>

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/btn_2"
        android:text="replace"/>

    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/framelayout"
        android:background="#00BCD4"/>

</LinearLayout>

fragment_blank.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".BlankFragment1">

    <!-- TODO: Update blank fragment layout -->

    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="@string/hello_blank_fragment" />

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/btn_3"
        android:layout_gravity="center"
        android:text="数据传递"/>

</FrameLayout>

fragment_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="horizontal">

    <TextView
        android:id="@+id/item_number"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="@dimen/text_margin"
        android:textAppearance="?attr/textAppearanceListItem" />

    <TextView
        android:id="@+id/content"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="@dimen/text_margin"
        android:textAppearance="?attr/textAppearanceListItem" />
</LinearLayout>

Fragment生命周期

onAttach()用来与Activity进行绑定，onCreate()对Bundle进行解析，onCreateView()进行ui进行解析，必须要重构的数据要在onResume()中获取，创建的时候从小到大，销毁的时候从大到小

加入些调试信息观察生命周期

BlankFragment1

package a.b.c.fragmentmangers;

import android.content.Context;
import android.os.Bundle;

import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;

import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.Toast;

/**
 * A simple {@link Fragment} subclass.
 * Use the {@link BlankFragment1#newInstance} factory method to
 * create an instance of this fragment.
 */
public class BlankFragment1 extends Fragment {

    // TODO: Rename parameter arguments, choose names that match
    // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";
    private static final String TAG = "BlankFragment1";

    // TODO: Rename and change types of parameters
    private String mParam1;
    private String mParam2;
    private View rootview;

    public BlankFragment1() {
        // Required empty public constructor

    }

    /**
     * Use this factory method to create a new instance of
     * this fragment using the provided parameters.
     *
     * @param param1 Parameter 1.
     * @param param2 Parameter 2.
     * @return A new instance of fragment BlankFragment1.
     */
    // TODO: Rename and change types and number of parameters
    public static BlankFragment1 newInstance(String param1, String param2) {
        BlankFragment1 fragment = new BlankFragment1();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onAttach(@NonNull Context context) {
        super.onAttach(context);
        Log.d(TAG, "onAttach: ");
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Bundle bundle = this.getArguments();
        String string = bundle.getString("lele");
        Log.i("lele",string);
    
        if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);
        }
        Log.d(TAG,"onCrate: ");
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        if(rootview == null){
            rootview = inflater.inflate(R.layout.frament_blank1,container,false);
        }
        Button btn = rootview.findViewById(R.id.btn_3);
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                //fragmentCallback.sendMsgToActivity("hello, I`m from Fragment");
                String message = fragmentCallback.getMsgFromActivity("null");
                Toast.makeText(BlankFragment1.this.getContext(),message,Toast.LENGTH_SHORT).show();
            }
        });
        Log.d(TAG,"onCreateView:");
        return rootview;
    }

    @Override
    public void onResume(){
        super.onResume();
        Log.d(TAG,"onResume:");
    }

    @Override
    public void onPause(){
        super.onPause();
        Log.d(TAG,"onPause");
    }

    @Override
    public void onStop(){
        super.onStop();
        Log.d(TAG,"onStop");
    }

    @Override
    public void onDestroyView(){
        super.onDestroyView();
        Log.d(TAG,"onDestroView");
    }

    @Override
    public void onDestroy(){
        super.onDestroy();
        Log.d(TAG,"onDestory");
    }





    private IFragmentCallback fragmentCallback;
    public void setFragmentCallback(IFragmentCallback callback){
        fragmentCallback = callback;
    }

}

Fragment生命周期注意事项‘

ViewPager2基本应用

MainActivity.java

package a.b.c.viewpagerandfragment;

import android.os.Bundle;

import androidx.activity.EdgeToEdge;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;
import androidx.recyclerview.widget.RecyclerView;
import androidx.viewpager2.widget.ViewPager2;

public class MainActivity extends AppCompatActivity{
    @Override
    protected void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        
        ViewPager2 viewPager = findViewById(R.id.viewPager);
        ViewPagerAdapter viewPagerAdapter = new ViewPagerAdapter();
        viewPager.setAdapter(viewPagerAdapter);
    }
}

ViewPagerAdaper.java

package a.b.c.viewpagerandfragment;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import androidx.constraintlayout.widget.ConstraintLayout;

import java.util.ArrayList;
import java.util.List;

public class ViewPagerAdapter extends RecyclerView.Adapter<ViewPagerAdapter.ViewPagerViewHolder>{
    private List<String> titles = new ArrayList<>();
    ViewPagerAdapter(){
        titles.add("hhh");
        titles.add("lelel");
         titles.add("hhh");
        titles.add("lelel");
         titles.add("hhh");
        titles.add("lelel");
         titles.add("hhh");
        titles.add("lelel");
         titles.add("hhh");
        titles.add("lelel");
    }
    @NonNull
    @Override
    public ViewPagerViewHolder onCreateViewHolder(@NonNull ViewGroup parent,int viewType){
        return new ViewPagerViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.item_pager,parent,flase));
        
        /*详细解释
LayoutInflater.from(parent.getContext())

LayoutInflater 是一个 Android 类，用于从 XML 布局文件中创建视图对象。from(parent.getContext()) 获取一个 LayoutInflater 实例，使用的是 parent 视图组的上下文 (Context)。

通过 parent.getContext() 获取 Context，因为 LayoutInflater 需要一个 Context 对象来访问资源并膨胀布局。

.inflate(R.layout.item_pager, parent, false)

inflate 方法用于将 XML 布局文件转换成实际的视图对象。这里，它将 R.layout.item_pager 布局文件中的视图膨胀成一个 View 对象。

R.layout.item_pager 是布局资源的 ID，代表你要膨胀的布局文件。item_pager.xml 中定义的视图将被加载到内存中。

parent 是 ViewGroup，它指定了布局的父视图组。在膨胀布局时，将这个 parent 传递进去可以确保正确设置视图的布局参数。

false 表示膨胀后的视图不会立即被附加到 parent 上。将其设置为 false 可以防止布局在膨胀时立刻附加到父视图，这样通常可以更好地控制视图的布局过程。

new ViewPagerViewHolder(...)

使用膨胀出来的 View 对象来创建一个新的 ViewPagerViewHolder 实例。ViewPagerViewHolder 是你定义的 RecyclerView.ViewHolder 子类，用于在 RecyclerView 中持有和管理视图。

在 ViewPagerViewHolder 的构造函数中，传入膨胀后的视图（itemView）用于初始化持有者的视图引用。

作用
这段代码的整体作用是创建一个新的 ViewPagerViewHolder 实例，并将其与通过 item_pager.xml 膨胀出的视图相关联。ViewPagerViewHolder 负责持有和管理 RecyclerView 中每个项的视图。在 onCreateViewHolder 方法中，你使用这段代码来为 RecyclerView 创建并返回一个新的视图持有者对象。
总结
膨胀布局：从 XML 布局文件 item_pager.xml 中膨胀出一个视图。
创建持有者：使用膨胀出的视图创建一个 ViewPagerViewHolder 实例。
返回持有者：将创建的视图持有者返回给 RecyclerView。
这样，RecyclerView 就可以使用这个视图持有者来显示和管理列表项。*/
    }
    @Override
    public void onBindViewHolder(@NoNull viewPagerViewHold holder,int position){
        holder.mTv.setText(tiltles.get(positon));
    }
    @Ovrride
    public int getItemCount(){
        return 10;
    }
    class ViewPagerViewHolder extends RecycleView.ViewHolder{
        TextView mTv;
        ConstraintLayout mContainer;
        public ViewPagerViewHolder(@NoNull View itemView){
            super(itemView);
            
            mContainer = itemView.findViewById(R.id.container);
            mTv = itemView.findViewById(R.id.tvTitle);
        }
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:layout_height="match_parent"
    android:layout_width="match_parent"
    xmlns:android="http://schemas.android.com/apk/res/android">
    <androidx.viewpager2.widget.ViewPager2
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/viewPager"
        android:background="#03A9F4">

    </androidx.viewpager2.widget.ViewPager2>

</LinearLayout>

item_pager.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/container">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/tvTitle"
        android:gravity="center"
        android:textColor="#2196F3"
        android:text="lele"
        android:textSize="50dp"
        />

</androidx.constraintlayout.widget.ConstraintLayout>

ViewPager2页面的切换

在color.xml文件中定义颜色

color.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <color name="black">#FF000000</color>
    <color name="white">#FFFFFFFF</color>
    <color name="red">#FF4411</color>
    <color name="colorPrimary">#6200EE</color>
    <color name="colorAccent">#03DAC5</color>
    <color name="colorPrimaryDark">#3700B3</color>
</resources>

ViewPagerAdapter.java

package a.b.c.viewpagerandfragment;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import androidx.constraintlayout.widget.ConstraintLayout;

import java.util.ArrayList;
import java.util.List;

public class ViewPagerAdapter extends RecycleView.Adapter<ViewPagerAdater.ViewPagerViewHolder>{
    private List<String> titles = new ArrayList<>();
    private List<Integer> colors = new ArrayList<>();
    ViewPagerAdapter(){
                titles.add("1");
        titles.add("2");
        titles.add("3");
        titles.add("4");
        titles.add("5");
        titles.add("6");
        titles.add("7");
        titles.add("8");
        titles.add("9");
        titles.add("10");

        colors.add(R.color.white);
        colors.add(R.color.colorAccent);
        colors.add(R.color.black);
        colors.add(R.color.red);
        colors.add(R.color.white);
        colors.add(R.color.colorPrimaryDark);
        colors.add(R.color.white);
        colors.add(R.color.colorAccent);
        colors.add(R.color.red);
        colors.add(R.color.colorAccent);
    }
    @NonNull
    @Override
    public ViewPagerViewHolder onCreateViewHolder(@NonNull ViewGruop parent,int viewType){
        return new ViewPagerViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.item_pager,parent,false));
    }
    
    @Override
    public void onBindViewHolder(@NonNull ViewPagerViewHolder holder,int position){
        holder.mTv.setText(titles.get(position));
        holder.mContainer.setBackgroumdResource(colors.get(position));
    }
    @Override
    public int getItemCount(){
        return 0;
    }
    class ViewPagerViewHolder extends RecyclerView.ViwHolder{
        TextView mTv;
        ConstrainLayout mContainer;
        public ViewPagerViewHolder(@NonNUll View itemView){
            super(itemView);
            
            mContainer = itemView.findViewById(R.id.container);
            mTv = itemView.finViewById(R.id.tvTitle);
        }
    }
}

Fragment与ViewPager合集

MainActivity.java

package a.b.c.wechatpage;

import android.os.Bundle;

import androidx.activity.EdgeToEdge;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;
import androidx.fragment.app.Fragment;
import androidx.viewpager2.widget.ViewPager2;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity{
    ViewPager2 viewPager;
    @Override
    protected void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ininPager();
    }
    private void initPager(){
        viewPager = findViewById(R.id.id_viewpager);
        ArrayList<Fragment> fragment=new ArrayList<>();
        fragments.add(BlankFragment.newInstance("微信聊天"));
        fragments.add(BlankFragment.newInstance("通讯录"));
        fragments.add(BlankFragment.newInstance("聊天"));
        fragments.add(BlankFragment.newInstance("发现"));
        fragments.add(BlankFrament.newInstance("我"));
        
        MyFragmentPagerAdapter pagerAdapter = new MyFragmentPagerAdapter(getSupportFragment(),getLifecycle(),fragments);
        viewPager.setAdapter(pagerAdapter);
    }
}

MyFragmentPagerAdapter.java

public class MyFragmentPagerAdapter extends FragmentStateAdapter{
    List<Fragment>fragmenList=new ArrayList<>();
    public MyFragmentPagerAdapter(@NonNull FragmentManager fragmentManager,@NonNull Lifecycle,List<Fragment>fragments){
        super(fragmentManager,lifecycle);
        fragmetnList=fragments;
    }
    @NonNull
    @Override
    public Fragment createFragment(int position){
        return fragmentList.get(position);
        
    }
    @Override
    public int getItemCount(){
        return fragmentList.size(); 
}

BlankFragment.java

import android.os.Bundle;

import androidx.fragment.app.Fragment;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class BlankFragment extends Fragment{
    View rootView;
    private static final String ARG_TEXT = "param1";
    private String mTextString;
    public BlankFragment(){
        
    }
    public static BlanFragment newInstance(String param1){
        BlankFragment fragment = new BlankFragment();
        Bundle args = new Bundle();
        args.putString(ARG_TEXT,param1);
        fragment.setArguments(args);
        return fragment;
    }
    @Override
    public void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        if(getArguments!=null){
            mTextString = getArguments().getString(ARG_TEXT);
        }
    }
    @Override
    public View onCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState){
        if(rootView = null){
            rootView = inflater.inflate(R.layout.fragment_blank,container,false);
        }
        initView();
        return rootView;
    }
    
    private void initView(){
        TextView textView = rootView.findViewById(R.id.text);
        textView.seetText(mTextString);
    }
}

activity_main.xml

注意：orientation要设置，否则无法正常显示

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">
    
    <androidx.viewpager2.widget.ViewPager2
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:id="@+id/id_viewpager"
        />
</LinearLayout>

fragment_blank.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".BlankFragment">

    <!-- TODO: Update blank fragment layout -->
    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:textSize="36sp"
        android:id="@+id/text"
        android:text="@string/hello_blank_fragment" />

</FrameLayout>

ViewPager+fragment模仿微信页面

android:layout_gravity: 控制视图相对于其父视图的位置。

android:gravity: 控制视图内部内容的位置和对齐方式。