Android 使用Fragment界面向下跳轉並一級級返回

1.首先貼上項目結構圖：

2.先添加一個接口文件BackHandledInterface.java,定義一個setSelectedFragment方法用於設置當前加載的Fragment在棧頂，主界面MainActivity須實現此接口，代碼如下：

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

3.定義一個抽象類BackHandledFragment繼承自Fragment，后面跳轉的Fragment界面都要繼承自BackHandledFragment。抽象類BackHandledFragment中定義一個返回值為boolean類型的onBackPressed方法，用於處理點擊返回按鍵（物理Back鍵）時的邏輯，若該方法返回false，表示當前Fragment不消費返回事件，而由Fragment所屬的FragmentActivity來處理這個事件。代碼如下：

package com.example.testdemo;  2 
import android.os.Bundle;  4 import android.support.v4.app.Fragment;  5 
public abstract class BackHandledFragment extends Fragment {  7 
    protected BackHandledInterface mBackHandledInterface;  9 
    /**
 * 所有繼承BackHandledFragment的子類都將在這個方法中實現物理Back鍵按下后的邏輯 12      */
    protected abstract boolean onBackPressed(); 14 
 @Override 16     public void onCreate(Bundle savedInstanceState) { 17         super.onCreate(savedInstanceState); 18         if (!(getActivity() instanceof BackHandledInterface)) { 19             throw new ClassCastException( 20                     "Hosting Activity must implement BackHandledInterface"); 21         } else { 22             this.mBackHandledInterface = (BackHandledInterface) getActivity(); 23  } 24  } 25 
 @Override 27     public void onStart() { 28         super.onStart(); 29         // 告訴FragmentActivity，當前Fragment在棧頂
        mBackHandledInterface.setSelectedFragment(this); 31  } 32 
}

4.主界面MainActivity要繼承FragmentActivity才能調用getSupportFragmentManager()方法來處理Fragment。MainActivity還需重寫onBackPressed方法用來捕捉返回鍵（Back Key）事件，代碼如下：

package com.example.testdemo;  2 
import android.os.Bundle;  4 import android.support.v4.app.FragmentActivity;  5 import android.support.v4.app.FragmentManager;  6 import android.support.v4.app.FragmentTransaction;  7 import android.view.View;  8 import android.view.View.OnClickListener;  9 import android.widget.Button; 10 
public class MainActivity extends FragmentActivity implements
 BackHandledInterface { 13     private static MainActivity mInstance; 14     private BackHandledFragment mBackHandedFragment; 15     private Button btnSecond; 16 
 @Override 18     public void onCreate(Bundle savedInstanceState) { 19         super.onCreate(savedInstanceState); 20  setContentView(R.layout.activity_main); 21         btnSecond = (Button) findViewById(R.id.btnSecond); 22         btnSecond.setOnClickListener(new OnClickListener() { 23 
 @Override 25             public void onClick(View v) { 26                 FirstFragment first = new FirstFragment(); 27  loadFragment(first); 28  btnSecond.setVisibility(View.GONE); 29  } 30  }); 31 
 } 33 
    public static MainActivity getInstance() { 35         if (mInstance == null) { 36             mInstance = new MainActivity(); 37  } 38         return mInstance; 39  } 40 
    public void loadFragment(BackHandledFragment fragment) { 42         BackHandledFragment second = fragment; 43         FragmentManager fm = getSupportFragmentManager(); 44         FragmentTransaction ft = fm.beginTransaction(); 45         ft.replace(R.id.firstFragment, second, "other"); 46         ft.addToBackStack("tag"); 47  ft.commit(); 48  } 49 
 @Override 51     public void setSelectedFragment(BackHandledFragment selectedFragment) { 52         this.mBackHandedFragment = selectedFragment; 53  } 54 
 @Override 56     public void onBackPressed() { 57         if (mBackHandedFragment == null || !mBackHandedFragment.onBackPressed()) { 58             if (getSupportFragmentManager().getBackStackEntryCount() == 0) { 59                 super.onBackPressed(); 60             } else { 61                 if (getSupportFragmentManager().getBackStackEntryCount() == 1) { 62  btnSecond.setVisibility(View.VISIBLE); 63  } 64  getSupportFragmentManager().popBackStack(); 65  } 66  } 67  } 68 }

5.分別添加兩個子級Fragment，FirstFragment.java和SecondFragment.java,代碼分別如下：

FirstFragment.java

package com.example.testdemo;  2 
import android.os.Bundle;  4 import android.support.annotation.Nullable;  5 import android.support.v4.app.FragmentManager;  6 import android.support.v4.app.FragmentTransaction;  7 import android.view.LayoutInflater;  8 import android.view.View;  9 import android.view.View.OnClickListener; 10 import android.view.ViewGroup; 11 import android.widget.Button; 12 
public class FirstFragment extends BackHandledFragment { 14     private View myView; 15     private Button btnSecond; 16 
 @Override 18     public View onCreateView(LayoutInflater inflater, 19  @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { 20         myView = inflater.inflate(R.layout.fragment_first, null); 21  initView(); 22         return myView; 23  } 24 
    private void initView() { 26         btnSecond = (Button) myView.findViewById(R.id.btnSecond); 27         btnSecond.setOnClickListener(new OnClickListener() { 28 
 @Override 30             public void onClick(View v) { 31                 SecondFragment second = new SecondFragment(); 32                 FragmentManager fm = getFragmentManager(); 33                 FragmentTransaction ft = fm.beginTransaction(); 34  ft.replace(R.id.firstFragment, second); 35                 ft.addToBackStack("tag"); 36  ft.commit(); 37  } 38  }); 39  } 40 
 @Override 42     protected boolean onBackPressed() { 43         return false; 44  } 45 
}

SecondFragment.java

package com.example.testdemo;  2 
import android.os.Bundle;  4 import android.support.annotation.Nullable;  5 import android.view.LayoutInflater;  6 import android.view.View;  7 import android.view.ViewGroup;  8 
public class SecondFragment extends BackHandledFragment { 10 
    private View mView; 12 
 @Override 14     public View onCreateView(LayoutInflater inflater, 15  @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { 16         mView = inflater.inflate(R.layout.fragment_second, null); 17         return mView; 18  } 19 
 @Override 21     protected boolean onBackPressed() { 22         return false; 23  } 24 
}

6.三個布局文件代碼如下：
activity_main.xml

<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  8         android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:text="FragmentActivity 父界面"
        android:textSize="26sp" />

    <Button 15         android:id="@+id/btnSecond"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:text="跳轉到FirstFragment" />

    <FrameLayout 22         android:id="@+id/firstFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent" >
    </FrameLayout>

</RelativeLayout>

 

fragment_first.xml

<?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="打開SecondFragment" />

</RelativeLayout>

 

fragment_second.xml

<?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  9         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.最后奉上實例鏈接：

http://files.cnblogs.com/_ymw/TestDemo