Android 使用Fragment界面向下跳转并一级级返回

http://www.cnblogs.com/_ymw/p/4227862.html

1.首先贴上项目结构图：

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：

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：

 1 package com.example.testdemo;
 2
 3 import android.os.Bundle;
 4 import android.support.v4.app.Fragment;
 5
 6 public abstract class BackHandledFragment extends Fragment {
 7
 8     protected BackHandledInterface mBackHandledInterface;
 9
10     /**
11      * 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
12      */
13     protected abstract boolean onBackPressed();
14
15     @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
26     @Override
27     public void onStart() {
28         super.onStart();
29         // 告诉FragmentActivity，当前Fragment在栈顶
30         mBackHandledInterface.setSelectedFragment(this);
31     }
32
33 }

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：

 1 package com.example.testdemo;
 2
 3 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
11 public class MainActivity extends FragmentActivity implements
12         BackHandledInterface {
13     private static MainActivity mInstance;
14     private BackHandledFragment mBackHandedFragment;
15     private Button btnSecond;
16
17     @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
24             @Override
25             public void onClick(View v) {
26                 FirstFragment first = new FirstFragment();
27                 loadFragment(first);
28                 btnSecond.setVisibility(View.GONE);
29             }
30         });
31
32     }
33
34     public static MainActivity getInstance() {
35         if (mInstance == null) {
36             mInstance = new MainActivity();
37         }
38         return mInstance;
39     }
40
41     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
50     @Override
51     public void setSelectedFragment(BackHandledFragment selectedFragment) {
52         this.mBackHandedFragment = selectedFragment;
53     }
54
55     @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.分别添加两个子级Fragment，FirstFragment.java和SecondFragment.java,代码分别如下：

FirstFragment.java

 1 package com.example.testdemo;
 2
 3 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
13 public class FirstFragment extends BackHandledFragment {
14     private View myView;
15     private Button btnSecond;
16
17     @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
25     private void initView() {
26         btnSecond = (Button) myView.findViewById(R.id.btnSecond);
27         btnSecond.setOnClickListener(new OnClickListener() {
28
29             @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
41     @Override
42     protected boolean onBackPressed() {
43         return false;
44     }
45
46 }

SecondFragment.java

 1 package com.example.testdemo;
 2
 3 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
 9 public class SecondFragment extends BackHandledFragment {
10
11     private View mView;
12
13     @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
20     @Override
21     protected boolean onBackPressed() {
22         return false;
23     }
24
25 }

6.三个布局文件代码如下：
activity_main.xml

 1 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
 2     xmlns:tools="http://schemas.android.com/tools"
 3     android:layout_width="match_parent"
 4     android:layout_height="match_parent"
 5     android:orientation="vertical" >
 6
 7     <TextView
 8         android:layout_width="wrap_content"
 9         android:layout_height="wrap_content"
10         android:layout_centerInParent="true"
11         android:text="FragmentActivity 父界面"
12         android:textSize="26sp" />
13
14     <Button
15         android:id="@+id/btnSecond"
16         android:layout_width="wrap_content"
17         android:layout_height="wrap_content"
18         android:layout_alignParentBottom="true"
19         android:text="跳转到FirstFragment" />
20
21     <FrameLayout
22         android:id="@+id/firstFragment"
23         android:layout_width="match_parent"
24         android:layout_height="match_parent" >
25     </FrameLayout>
26
27 </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="打开SecondFragment" />

</RelativeLayout>

fragment_second.xml

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
 3     android:layout_width="match_parent"
 4     android:layout_height="match_parent"
 5     android:background="#e5e5e5"
 6     android:orientation="vertical" >
 7
 8     <TextView
 9         android:layout_width="wrap_content"
10         android:layout_height="wrap_content"
11         android:layout_centerInParent="true"
12         android:text="SecondFragment"
13         android:textColor="#000000"
14         android:textSize="26sp" />
15
16 </RelativeLayout>

7.最后奉上实例链接：

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