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Android编程使用Fragment界面向下跳转并一级级返回的实现方法

转载 作者：qq735679552 更新时间：2022-09-27 22:32:09 25 4
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本文实例讲述了Android编程使用Fragment界面向下跳转并一级级返回的实现方法。分享给大家供大家参考，具体如下:

1.首先贴上项目结构图:

Android编程使用Fragment界面向下跳转并一级级返回的实现方法

2.先添加一个接口文件BackHandledInterface.java,定义一个setSelectedFragment方法用于设置当前加载的Fragment在栈顶，主界面MainActivity须实现此接口，代码如下:

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package com.example.testdemo;
public interface BackHandledInterface {
   public abstract void setSelectedFragment(BackHandledFragment selectedFragment);
}

3.定义一个抽象类BackHandledFragment继承自Fragment，后面跳转的Fragment界面都要继承自BackHandledFragment。抽象类BackHandledFragment中定义一个返回值为boolean类型的onBackPressed方法，用于处理点击返回按键（物理Back键）时的逻辑，若该方法返回false，表示当前Fragment不消费返回事件，而由Fragment所属的FragmentActivity来处理这个事件。代码如下:

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package com.example.testdemo;
import android.os.Bundle;
import android.support.v4.app.Fragment;
public abstract class BackHandledFragment extends Fragment {
   protected BackHandledInterface mBackHandledInterface;
   /**
    * 所有继承BackHandledFragment的子类都将在这个方法中实现物理Back键按下后的逻辑
    */
   protected abstract boolean onBackPressed();
   @Override
   public void onCreate(Bundle savedInstanceState) {
     super .onCreate(savedInstanceState);
     if (!(getActivity() instanceof BackHandledInterface)) {
       throw new ClassCastException(
           "Hosting Activity must implement BackHandledInterface" );
     } else {
       this .mBackHandledInterface = (BackHandledInterface) getActivity();
     }
   }
   @Override
   public void onStart() {
     super .onStart();
     // 告诉FragmentActivity，当前Fragment在栈顶
     mBackHandledInterface.setSelectedFragment( this );
   }
}

4.主界面MainActivity要继承FragmentActivity才能调用getSupportFragmentManager()方法来处理Fragment。MainActivity还需重写onBackPressed方法用来捕捉返回键（Back Key）事件，代码如下:

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package com.example.testdemo;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class MainActivity extends FragmentActivity implements
     BackHandledInterface {
   private static MainActivity mInstance;
   private BackHandledFragment mBackHandedFragment;
   private Button btnSecond;
   @Override
   public void onCreate(Bundle savedInstanceState) {
     super .onCreate(savedInstanceState);
     setContentView(R.layout.activity_main);
     btnSecond = (Button) findViewById(R.id.btnSecond);
     btnSecond.setOnClickListener( new OnClickListener() {
       @Override
       public void onClick(View v) {
         FirstFragment first = new FirstFragment();
         loadFragment(first);
         btnSecond.setVisibility(View.GONE);
       }
     });
   }
   public static MainActivity getInstance() {
     if (mInstance == null ) {
       mInstance = new MainActivity();
     }
     return mInstance;
   }
   public void loadFragment(BackHandledFragment fragment) {
     BackHandledFragment second = fragment;
     FragmentManager fm = getSupportFragmentManager();
     FragmentTransaction ft = fm.beginTransaction();
     ft.replace(R.id.firstFragment, second, "other" );
     ft.addToBackStack( "tag" );
     ft.commit();
   }
   @Override
   public void setSelectedFragment(BackHandledFragment selectedFragment) {
     this .mBackHandedFragment = selectedFragment;
   }
   @Override
   public void onBackPressed() {
     if (mBackHandedFragment == null || !mBackHandedFragment.onBackPressed()) {
       if (getSupportFragmentManager().getBackStackEntryCount() == 0 ) {
         super .onBackPressed();
       } else {
         if (getSupportFragmentManager().getBackStackEntryCount() == 1 ) {
           btnSecond.setVisibility(View.VISIBLE);
         }
         getSupportFragmentManager().popBackStack();
       }
     }
   }
}

5.分别添加两个子级Fragment，FirstFragment.java和SecondFragment.java,代码分别如下:

FirstFragment.java:

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package com.example.testdemo;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
public class FirstFragment extends BackHandledFragment {
   private View myView;
   private Button btnSecond;
   @Override
   public View onCreateView(LayoutInflater inflater,
       @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
     myView = inflater.inflate(R.layout.fragment_first, null );
     initView();
     return myView;
   }
   private void initView() {
     btnSecond = (Button) myView.findViewById(R.id.btnSecond);
     btnSecond.setOnClickListener( new OnClickListener() {
       @Override
       public void onClick(View v) {
         SecondFragment second = new SecondFragment();
         FragmentManager fm = getFragmentManager();
         FragmentTransaction ft = fm.beginTransaction();
         ft.replace(R.id.firstFragment, second);
         ft.addToBackStack( "tag" );
         ft.commit();
       }
     });
   }
   @Override
   protected boolean onBackPressed() {
     return false ;
   }
}

SecondFragment.java:

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package com.example.testdemo;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
public class SecondFragment extends BackHandledFragment {
   private View mView;
   @Override
   public View onCreateView(LayoutInflater inflater,
       @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
     mView = inflater.inflate(R.layout.fragment_second, null );
     return mView;
   }
   @Override
   protected boolean onBackPressed() {
     return false ;
   }
}

6.三个布局文件代码如下:

activity_main.xml:

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< RelativeLayout 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"
   android:orientation = "vertical" >
   < TextView
     android:layout_width = "wrap_content"
     android:layout_height = "wrap_content"
     android:layout_centerInParent = "true"
     android:text = "FragmentActivity 父界面"
     android:textSize = "26sp" />
   < Button
     android:id = "@+id/btnSecond"
     android:layout_width = "wrap_content"
     android:layout_height = "wrap_content"
     android:layout_alignParentBottom = "true"
     android:text = "跳转到FirstFragment" />
   < FrameLayout
     android:id = "@+id/firstFragment"
     android:layout_width = "match_parent"
     android:layout_height = "match_parent" >
   </ FrameLayout >
</ RelativeLayout >

fragment_first.xml:

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<? xml version = "1.0" encoding = "utf-8" ?>
< RelativeLayout xmlns:android = "http://schemas.android.com/apk/res/android"
   android:layout_width = "match_parent"
   android:layout_height = "match_parent"
   android:background = "#e5e5e5"
   android:orientation = "vertical" >
   < TextView
     android:layout_width = "wrap_content"
     android:layout_height = "wrap_content"
     android:layout_centerInParent = "true"
     android:text = "FirstFragment"
     android:textColor = "#000000"
     android:textSize = "26sp" />
   < Button
     android:id = "@+id/btnSecond"
     android:layout_width = "wrap_content"
     android:layout_height = "wrap_content"
     android:layout_alignParentBottom = "true"
     android:text = "打开SecondFragment" />
</ RelativeLayout >

fragment_second.xml:

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<? xml version = "1.0" encoding = "utf-8" ?>
< RelativeLayout xmlns:android = "http://schemas.android.com/apk/res/android"
   android:layout_width = "match_parent"
   android:layout_height = "match_parent"
   android:background = "#e5e5e5"
   android:orientation = "vertical" >
   < TextView
     android:layout_width = "wrap_content"
     android:layout_height = "wrap_content"
     android:layout_centerInParent = "true"
     android:text = "SecondFragment"
     android:textColor = "#000000"
     android:textSize = "26sp" />
</ RelativeLayout >

7.最后奉上实例链接:

完整实例代码代码点击此处本站下载.

希望本文所述对大家Android程序设计有所帮助.

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