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。