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。