Android开发之Fragment动态添加与管理

主界面布局资源

在activity_main.xml中，声明两个按钮备用，再加入一个帧布局，待会儿用来展示Fragment。

<?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:layout_width="match_parent"android:layout_height="match_parent"android:orientation="vertical"tools:context=".MainActivity"><Buttonandroid:layout_width="match_parent"android:layout_height="wrap_content"android:id="@+id/button1"android:text="@string/push"/><Buttonandroid:layout_width="match_parent"android:layout_height="wrap_content"android:id="@+id/button2"android:text="@string/replace"/><FrameLayoutandroid:layout_width="match_parent"android:layout_height="match_parent"android:id="@+id/framelayout"android:background="@color/purple_200"/></LinearLayout>

两个工具Fragment

用来展示的Fragment，随便找两个AS预设的即可，这里使用的是一个BlankFragment和一个ItemFragment。
BlankFragment：

<?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 --><TextViewandroid:layout_width="match_parent"android:layout_height="match_parent"android:text="@string/hello_blank_fragment" /></FrameLayout>

package com.example.dynamicfragment;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_NUMBERprivate static final String ARG_PARAM1 = "param1";private static final String ARG_PARAM2 = "param2";// TODO: Rename and change types of parametersprivate 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 parameterspublic 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;}@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);if (getArguments() != null) {mParam1 = getArguments().getString(ARG_PARAM1);mParam2 = getArguments().getString(ARG_PARAM2);}}@Overridepublic View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {// Inflate the layout for this fragmentreturn inflater.inflate(R.layout.fragment_blank1, container, false);}
}

ItemFragment：

<?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="com.example.dynamicfragment.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" />

package com.example.dynamicfragment;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 com.example.dynamicfragment.placeholder.PlaceholderContent;/*** A fragment representing a list of Items.*/
public class ItemFragment extends Fragment {// TODO: Customize parameter argument namesprivate static final String ARG_COLUMN_COUNT = "column-count";// TODO: Customize parametersprivate 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;}@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);if (getArguments() != null) {mColumnCount = getArguments().getInt(ARG_COLUMN_COUNT);}}@Overridepublic View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {View view = inflater.inflate(R.layout.fragment_item_list, container, false);// Set the adapterif (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;}
}

主程序

在主程序里，我们要实现点击按钮显示不同的Fragment。这里使用一种新的实现按钮方式，在声明MainActivity类的时候引用View.OnClickListener接口，然后在button1.setOnClickListener(this);中传入this，这样按钮被点击时就会自动调用后面写的OnClick函数。

在OnClick函数被调用时，我们判断是哪一个按钮被点击了，然后根据按钮ID将不同的Fragment展现在帧布局上。

package com.example.dynamicfragment;import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentTransaction;import android.os.Bundle;
import android.view.View;
import android.widget.Button;public class MainActivity extends AppCompatActivity implements View.OnClickListener{@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);Button button1 = findViewById(R.id.button1);Button button2 = findViewById(R.id.button2);button1.setOnClickListener(this);button2.setOnClickListener(this);}@Overridepublic void onClick(View view) {switch (view.getId()){case R.id.button1:replaceFragment(new BlankFragment1());break;case R.id.button2:replaceFragment(new ItemFragment());break;}}private void replaceFragment(Fragment fragment) {FragmentManager fragmentManager = getSupportFragmentManager();FragmentTransaction transaction = fragmentManager.beginTransaction();transaction.replace(R.id.framelayout, fragment);//创建replace事件transaction.addToBackStack(null);transaction.commit();//执行transaction中的事件}
}

还需要重点讲解一下的是replaceFragment函数中的栈，transaction.addToBackStack(null);中的null指代的是默认栈。加入该语句后，每次更新都会向栈中加入一个Fragment，且屏幕上显示的即是栈顶的Fragment。当我们点击返回按钮时，栈顶的Fragment被弹出，屏幕上显示下一个Fragment。

试验如下，交替点击两个按钮若干次，屏幕上会依次出现两个Fragment交替覆盖，而点击返回按钮后，最顶上Fragment则会被撤除。