Android编程使用Fragment界面向下跳转并一级级返回的实现方法

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：

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：

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：

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：

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：

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：

<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：

<?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：

<?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。