Android-Fragment(上)

发表于 分类于 本文字数： 20k

  Fragment必须嵌入在Activity中使用，因此，虽然Fragment有自己的生命周期，但会受它所在的Activity的生命周期的控制

在MainActivity中使用Fragment

①创建fragment

创建一个普通的fragment

创建完毕后会自动生成对应的xml布局

②修改BlankFragment.java

删掉其中无用的代码

删除完毕后

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import android.os.Bundle;
import androidx.fragment.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;


public class BlankFragment extends Fragment {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_blank, container, false);
    }
}

优化onCreateView

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//    优化返回值写法，使其不会一直创建
    private View root;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        if (root == null){
            root = inflater.inflate(R.layout.fragment_blank,container,false);
        }
        return root;
    }

③修改两个Fragment的布局

BlankFragment1

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<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:layout_height="match_parent"
    android:layout_width="match_parent"
    android:orientation="vertical"
    android:gravity="center_horizontal"
    xmlns:android="http://schemas.android.com/apk/res/android">
    <TextView
        android:text="BlankFragment1"
        android:textSize="20sp"
        android:textColor="@color/black"
        android:textStyle="bold"
        android:id="@+id/blankFragmentText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
    <Button
        android:text="按钮"
        android:id="@+id/blankFragmentButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
</LinearLayout>

BlankFragment2

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<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:layout_height="match_parent"
    android:layout_width="match_parent"
    android:orientation="vertical"
    android:gravity="center_horizontal"
    xmlns:android="http://schemas.android.com/apk/res/android">
    <TextView
        android:text="BlankFragment2"
        android:textSize="20sp"
        android:textColor="#ff0033"
        android:textStyle="bold"
        android:id="@+id/blankFragmentText2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
    <Button
        android:text="按钮"
        android:id="@+id/blankFragmentButton2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
</LinearLayout>

④添加至MainActivity布局

  打开MainActivity的布局资源文件activity_main.xml，在其中插入fragment

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<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    xmlns:android="http://schemas.android.com/apk/res/android">
    <Button
        android:text="replaceFragment1"
        android:textAllCaps="false"
        android:id="@+id/replaceFragment1"
        android:layout_alignParentBottom="true"
        android:layout_marginBottom="60dp"
        android:layout_width="wrap_content"
        android:layout_marginLeft="20dp"
        android:layout_height="wrap_content"/>
    <Button
        android:text="replaceFragment2"
        android:textAllCaps="false"
        android:id="@+id/replaceFragment2"
        android:layout_marginRight="20dp"
        android:layout_marginBottom="60dp"
        android:layout_alignParentRight="true"
        android:layout_alignParentBottom="true"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
    <FrameLayout
        android:background="#ccffcc"
        android:id="@+id/frameLayout1"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:id="@+id/linearLayout1"
            android:orientation="vertical">
<!--            插入的两个fragment布局-->
            <fragment
                android:id="@+id/mainActivityFragment1"
                android:name="com.a.fragment.BlankFragment1"
                android:layout_width="match_parent"
                android:layout_weight="1"
                android:layout_height="match_parent"/>
            <fragment
                android:id="@+id/mainActivityFragment2"
                android:name="com.a.fragment.BlankFragment2"
                android:layout_width="match_parent"
                android:layout_weight="1"
                android:layout_height="match_parent"/>
        </LinearLayout>
    </FrameLayout>
</RelativeLayout>


   1. 插入在activity_main.xml中的fragment一定要有id
   2. 插入在activity_main.xml中的fragment一定要有name(BlankFragment的完整类名)属性

给fragment添加事件

fragment首次绘制界面时调用onCreateView，所以可以在onCreateView下写代码

给BlankFragment的按钮写事件(两个fragment一样的)

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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 implements View.OnClickListener{
    private View root;
    private TextView blankFragmentText;
    private Button blankFragmentButton;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        if (root == null){
            root = inflater.inflate(R.layout.fragment_blank1,container,false);
        }
        blankFragmentButton = root.findViewById(R.id.blankFragmentButton);
        blankFragmentText = root.findViewById(R.id.blankFragmentText);
//        给按钮添加OnClick
        blankFragmentButton.setOnClickListener(this);
        return root;
    }

    @Override
    public void onClick(View v) {
        blankFragmentText.setText("Welcome BlankFragment1");
    }
}

③效果

MainActivity页显示两个Fragment互不影响(两个Fragment甚至可以来自同一个BlankFragment.java，即name属性都为com.a.fragment.BlankFragment1)

动态添加fragment

  在动态添加fragment前一定要搞懂FragmentManager类

①两种fragment

  fragment分为app包内的fragment和v4包内的fragment

二者在使用上的区别：

  1. app包中的fragment兼容自3.0起以后的版本，v4包中的fragment可以兼容到1.6的版本
  2. app.fragment使用标签时。v4.fragment使用标签时，当这个Activity的布局中有标签，必须，如果不继成FragmentActivity的话 编译系统会把认为是app包中的Fragment来处理。但是此时我们导入的是v4包中的Fragment，所以会报错
  3. 对应的是v4包，对应的是app包

  在3.0版本之前使用fragment需借助V4包的getSupportFragmentManager()方法来间接获取FragmentManager()对象，3.0版本之后，可以通过Fragment的api直接使用getFragmentManager()方法获取FragmentManager()对象

  为什么我的MainActivity布局中使用v4的fragment，却继承AppCompatActivity而不是FragmentActivity？
  因为AppCompatActivity继承FragmentActivity，这样的话，MainActivity -继承-> AppCompatActivity -继承-> FragmentActivity

  Android studio创建MainActivity自动extends AppCompatActivity，为什么不extends Activity
  AppCompatActivity继承v4包的FragmentAvtivity，并且加入了很多新特性，可以更好的兼容旧系统

②FragmentManager(Fragment的管理)

  1. 顾名思义FragmentManager是Fragment的管理类
  2. getSupportFragmentManager()获取所在fragment 的父容器的管理器(getFragmentManager()同理)
  3. getSupportFragmentManager()或者getFragmentManager()获得FragmentManager对象, 可以认为Activity是FragmentManager的宿主环境类
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//通过getSupportFragmentManager()可以获取一个v4包的fragment管理类
FragmentManager fragmentManager = getSupportFragmentManager();

//通过getSupportFragmentManager()拿到fragmentManager的触发器FragmentTransaction
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();

//将fragment替换到R.id.frameLayout
fragmentTransaction.replace(R.id.frameLayout, fragment);//这里的fragment参数一个Fragment类创建的对象的变量

//执行
fragmentTransaction.commit();

③动态添加

1、创建至MainActivity

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//        获取v4包的Fragment的管理类
        FragmentManager fragmentManager = getSupportFragmentManager();
//        获取Transaction管理
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
//        将新fragment替换至指定id的控件内
        fragmentTransaction.replace(R.id.frameLayout1,fragment);
//        开始
        fragmentTransaction.commit();

2、fragment入栈
  在FragmentManager.transaction.addToBackStack();向栈中添加Fragment,从而实现添加Fragment后,可以实现按返回键依次返回上个Fragment

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//入栈
fragmentTransaction.addToBackStack(null);

3、完整代码

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import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.FrameLayout;
import android.widget.LinearLayout;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{
    private Button replaceFragment1,replaceFragment2;
    private FrameLayout frameLayout1;
    private LinearLayout linearLayout1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        replaceFragment1 = findViewById(R.id.replaceFragment1);
        replaceFragment2 = findViewById(R.id.replaceFragment2);
        frameLayout1 = findViewById(R.id.frameLayout1);
        linearLayout1 = findViewById(R.id.linearLayout1);

        replaceFragment1.setOnClickListener(this);
        replaceFragment2.setOnClickListener(this);
    }

    @Override
//    两个按钮的事件
    public void onClick(View v) {
//        隐藏FrameLayout里的LinearLayout
        linearLayout1.setVisibility(View.GONE);
        switch (v.getId()){
//            按钮一
            case R.id.replaceFragment1:
//                创建BlankFragment1
                BlankFragment1 blankFragment1 = new BlankFragment1();
                setReplaceFragment(blankFragment1);
                break;
//            按钮二
            case R.id.replaceFragment2:
//                创建BlankFragment2
                BlankFragment2 blankFragment2 = new BlankFragment2();
                setReplaceFragment(blankFragment2);
                break;
        }
    }

    private void setReplaceFragment (Fragment fragment){
//        获取v4包的Fragment的管理类
        FragmentManager fragmentManager = getSupportFragmentManager();
//        获取Transaction管理
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
//        将新fragment替换至指定id的控件内
        fragmentTransaction.replace(R.id.frameLayout1,fragment);
//        入栈
        fragmentTransaction.addToBackStack(null);
//        开始
        fragmentTransaction.commit();
    }
}

Fragment入栈后在回退时可以一个一个的返回

fragment的数据传递

fragment数据传递分三种模式，即

  1. Activity向Fragment传递数据(Activity发送，Fragment接收)
  2. Fragment向Activity传递数据(Fragment发送，Activity接收)
  3. Fragment向Fragment传递数据

①原生Bundle传递数据

  Bundle传递的数据，是以key-value(键值对)的形式存在的；传递的数据可以是boolean、byte、int、long、float、double、string等基本类型或它们对应的数组，也可以是对象或对象数组；当Bundle传递的是对象或对象数组时，必须实现Serializable 或Parcelable接口

传递基本类型

在MainActivity中发送

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//  创建数据传递对象
  Bundle bundle = new Bundle();
//  写入键值对
  bundle.putString("message1","Bundle方式传递的数据");
//  创建Fragment对象
  BlankFragment1 blankFragment1 = new BlankFragment1();
//  设置需要传递的Fragment参数
  blankFragment1.setArguments(bundle);
//  在setReplaceFragment方法将Fragment实例化
  setReplaceFragment(blankFragment1);

在Fragment中接收

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//  创建Bundle对象
  Bundle bundle = this.getArguments();
//  获取对应key的键值对
  String msg = bundle.getString("message");
//  输出
  Toast.makeText(getActivity(),msg,Toast.LENGTH_SHORT).show();

写入MainActivity和Fragment

先去删掉activity_main中FrameLayout的LinearLayout

MainActivity

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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;
import android.widget.FrameLayout;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{
    private Button replaceFragment1,replaceFragment2;
    private FrameLayout frameLayout1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        replaceFragment1 = findViewById(R.id.replaceFragment1);
        replaceFragment2 = findViewById(R.id.replaceFragment2);
        frameLayout1 = findViewById(R.id.frameLayout1);

        replaceFragment1.setOnClickListener(this);
        replaceFragment2.setOnClickListener(this);
    }

    @Override
//    两个按钮的事件
    public void onClick(View v) {
//        创建数据传递对象
        Bundle bundle = new Bundle();
        switch (v.getId()){
//            按钮一
            case R.id.replaceFragment1:
                BlankFragment1 blankFragment1 = new BlankFragment1();
//                设置需要传递的Fragment参数
                blankFragment1.setArguments(bundle);
//                写入键值对
                bundle.putString("message1","Bundle方式向BlankFragment1传递的数据");
                setReplaceFragment(blankFragment1);
                break;
//            按钮二
            case R.id.replaceFragment2:
                BlankFragment2 blankFragment2 = new BlankFragment2();
//                设置需要传递的Fragment参数
                blankFragment2.setArguments(bundle);
//                写入键值对
                bundle.putString("message1","Bundle方式向BlankFragment2传递的数据");
                setReplaceFragment(blankFragment2);
                break;
        }
    }

    private void setReplaceFragment (Fragment fragment){
        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
        fragmentTransaction.replace(R.id.frameLayout1,fragment);
        fragmentTransaction.addToBackStack(null);
        fragmentTransaction.commit();
    }
}

两个BlankFragment类似

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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;
import android.widget.Toast;

public class BlankFragment1 extends Fragment implements View.OnClickListener{
    private View root;
    private TextView blankFragmentText;
    private Button blankFragmentButton;
    private String msg;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
//        创建Bundle对象
        Bundle bundle = this.getArguments();
//        获取对应的键值对
        msg = bundle.getString("message1");
        Toast.makeText(getActivity(),msg,Toast.LENGTH_SHORT).show();
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        if (root == null){
            root = inflater.inflate(R.layout.fragment_blank1,container,false);
        }
        blankFragmentButton = root.findViewById(R.id.blankFragmentButton);
        blankFragmentText = root.findViewById(R.id.blankFragmentText);
        blankFragmentButton.setOnClickListener(this);
        return root;
    }

    @Override
    public void onClick(View v) {
        blankFragmentText.setText("Welcome BlankFragment1");
    }
}

②使用接口传递数据

创建接口
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public interface CallBack {
    String getMessage();
    void sendMessage(String msg);
}
BlankFragment中

1、让BlankFragment再继承一个OnLongClickListener，使单击时从MianActivity获取，长按时向MainActivity发送

2、用接口定义变量，并创建setCallBack方法供MainActivity调用

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//    用接口定义的变量
    private CallBack callBack;
//    在MianActivity中调用
    public void setCallBack(CallBack callBack){
        this.callBack = callBack;
    }

3、按钮单击时获取

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String str = callBack.getMessage();
Toast.makeText(getActivity(),"BlankFragment1:" + str,Toast.LENGTH_SHORT).show();

4、按钮长按时发送

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callBack.sendMessage("BlankFragment1发送的数据");
return true;

BlankFragment1.java

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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;
import android.widget.Toast;

public class BlankFragment1 extends Fragment implements View.OnClickListener,View.OnLongClickListener{
    private View root;
    private TextView blankFragmentText;
    private Button blankFragmentButton;
    private String msg;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
//        创建Bundle对象
        Bundle bundle = this.getArguments();
//        获取对应的键值对
        msg = bundle.getString("message1");
        Toast.makeText(getActivity(),msg,Toast.LENGTH_SHORT).show();
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        if (root == null){
            root = inflater.inflate(R.layout.fragment_blank1,container,false);
        }
        blankFragmentButton = root.findViewById(R.id.blankFragmentButton);
        blankFragmentText = root.findViewById(R.id.blankFragmentText);
//        按钮事件
        blankFragmentButton.setOnClickListener(this);
        blankFragmentButton.setOnLongClickListener(this);
        return root;
    }

//    用接口定义的变量
    private CallBack callBack;
//    在MianActivity中调用
    public void setCallBack(CallBack callBack){
        this.callBack = callBack;
    }

    @Override
    public void onClick(View v) {
        blankFragmentText.setText("Welcome BlankFragment1");
        String str = callBack.getMessage();
        Toast.makeText(getActivity(),"BlankFragment1:" + str,Toast.LENGTH_SHORT).show();
    }

    @Override
    public boolean onLongClick(View v) {
        callBack.sendMessage("BlankFragment1发送的数据");
        return true;
    }
}

MainActivity中

1、调用setCallBack方法

在按钮单击事件下通过已经创建好的blankFragment对象调用

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blankFragment1.setCallBack(new CallBack() {
    @Override
    public String getMessage() {
        return "MainActivity获取的数据";
    }
    @Override
    public void sendMessage(String msg) {
        Toast.makeText(MainActivity.this,"MainActivity:" + msg,Toast.LENGTH_SHORT).show();
    }
});

2、按钮二

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blankFragment2.setCallBack(new CallBack() {
    @Override
    public String getMessage() {
        return "MainActivity获取的数据";
    }
    @Override
    public void sendMessage(String msg) {
        Toast.makeText(MainActivity.this,"MainActivity:" + msg,Toast.LENGTH_SHORT).show();
    }
});

MainActivity.java

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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;
import android.widget.FrameLayout;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{
    private Button replaceFragment1,replaceFragment2;
    private FrameLayout frameLayout1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        replaceFragment1 = findViewById(R.id.replaceFragment1);
        replaceFragment2 = findViewById(R.id.replaceFragment2);
        frameLayout1 = findViewById(R.id.frameLayout1);

        replaceFragment1.setOnClickListener(this);
        replaceFragment2.setOnClickListener(this);
    }

    @Override
//    两个按钮的事件
    public void onClick(View v) {
//        创建数据传递对象
        Bundle bundle = new Bundle();
        switch (v.getId()){
//            按钮一
            case R.id.replaceFragment1:
                BlankFragment1 blankFragment1 = new BlankFragment1();
//                设置需要传递的Fragment参数
                blankFragment1.setArguments(bundle);
//                写入键值对
                bundle.putString("message1","Bundle方式向BlankFragment1传递的数据");
//                在setReplaceFragment方法将Fragment实例化
                setReplaceFragment(blankFragment1);

                blankFragment1.setCallBack(new CallBack() {
                    @Override
                    public String getMessage() {
                        return "MainActivity获取的数据";
                    }
                    @Override
                    public void sendMessage(String msg) {
                        Toast.makeText(MainActivity.this,"MainActivity:" + msg,Toast.LENGTH_SHORT).show();
                    }
                });
                break;
//            按钮二
            case R.id.replaceFragment2:
                BlankFragment2 blankFragment2 = new BlankFragment2();
//                设置需要传递的Fragment参数
                blankFragment2.setArguments(bundle);
//                写入键值对
                bundle.putString("message1","Bundle方式向BlankFragment2传递的数据");
//                在setReplaceFragment方法将Fragment实例化
                setReplaceFragment(blankFragment2);

                blankFragment2.setCallBack(new CallBack() {
                    @Override
                    public String getMessage() {
                        return "MainActivity获取的数据";
                    }
                    @Override
                    public void sendMessage(String msg) {
                        Toast.makeText(MainActivity.this,"MainActivity:" + msg,Toast.LENGTH_SHORT).show();
                    }
                });
                break;
        }
    }

    private void setReplaceFragment (Fragment fragment){
//        获取v4包的Fragment的管理类
        FragmentManager fragmentManager = getSupportFragmentManager();
//        获取Transaction管理
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
//        将新fragment替换至指定id的控件内
        fragmentTransaction.replace(R.id.frameLayout1,fragment);
//        入栈
        fragmentTransaction.addToBackStack(null);
//        开始
        fragmentTransaction.commit();
    }
}

效果图