导航到上一个片段，点击后退按钮:

Question

我有两个片段在我的活动fragment1和fragment2，我想当用户从fragment2点击后退按钮，它应该导航用户到fragement1

我的xml代码活动是:我正在设置片段在xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout     
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".Routeplan" >       
    <FrameLayout 
        android:id="@+id/content_frame_polymer"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" >               

          <viewpager.helper.JazzyViewPager 
                    xmlns:android="http://schemas.android.com/apk/res/android"
                    android:id="@+id/pager"
                    android:layout_width="fill_parent"
                    android:layout_height="fill_parent"         
                />      
    </FrameLayout>   
</android.support.v4.widget.DrawerLayout>

我的活动代码:

public class MainActivity extends FragmentActivity  {
    @Override
    protected void onCreate(Bundle arg0) {
        super.onCreate(arg0);
        setContentView(R.layout.packing_activity);
        mPager = (JazzyViewPager)findViewById(R.id.pager);      
        PagerAdapter padapter = new PagerAdapter(getSupportFragmentManager(),NUM_PAGES,mPager);     
        mPager.setAdapter(padapter);        
        mPager.setPageMargin(30);       
    } 
}

PagerAdapter代码:

public class PagerAdapter extends FragmentPagerAdapter {
    int NUM_PAGES;
    JazzyViewPager mPager;
    public PagerAdapter(FragmentManager fm, int numPages, JazzyViewPager mPager) {
        super(fm);  
        this.NUM_PAGES=numPages;
        this.mPager=mPager;
        // TODO Auto-generated constructor stub
    }
    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        Object obj = super.instantiateItem(container, position);
        mPager.setObjectForPosition(obj, position);
        return obj;
    }
    @Override
    public Fragment getItem(int arg0) {
        // TODO Auto-generated method stub
        switch (arg0) {
        case 0:                 
            return new Fragmentone();         
        case 1:                 
            return new Fragmenttwo();           
        default:
            break;
        }
        return null;
    }
    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return NUM_PAGES;
    }
}

Fragmentone代码:

public class FragmentOne extends Fragment { 
    private ViewGroup rootView1;
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {                
         return rootView1 = (ViewGroup) inflater
                .inflate(R.layout.about_rohtak, container, false);
    }
}

Fragmenttwo代码:

public class FragmentTwo extends Fragment { 
    private ViewGroup rootView1;
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {                
         return rootView1 = (ViewGroup) inflater
                .inflate(R.layout.about_rohtak, container, false);
    }
}

Answer 1

基本上，您必须覆盖活动上的onBackPressed方法，并将过程逻辑传递给Fragment。在Fragment中，您需要监听Activity中发生的事件。有一些选项如何实现这些事情，但我更喜欢通过接口通信，如果可能的话。这可以具体实现:

public MyActivity extends AppCompatActivity {
    private BackButtonListener backButtonListener;
    public interface BackButtonListener {
        void onBackButtonClicked();
    }
    public void setBackButtonListener(BackButtonListener backButtonListener) {
        this.backButtonListener = backButtonListener;           
    }
    public void onBackPressed() {
        if (null != backButtonListener) {
            backButtonListener.onBackButtonClicked();
        } else {
            super.onBackPressed();      
        }
    }
}
public MyFragment extends Fragment implements BackButtonListener {
    private ViewPager viewPager;
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        if (activity instanceof MyActivity) {
            ((MyActivity) activity).setBackButtonListener(this);
        }
    }
    public void onBackButtonClicked() {
        if (0 != viewPager.getCurrentItem()) {
            viewPager.setCurrentItem(viewPager.getCurrentItem() - 1);
        }
    }
}

Edited:要小心实现这个，因为你改变了自然的导航顺序。想想你如何处理后退按钮，然后viewpager的当前项目是第一个元素(位置0)。你应该如何告诉片段对象(BackButtonListener)不能处理这个，并传递回进程逻辑调用者或做其他事情。这要看情况。简而言之，总是在按下后退键时做一些有意义的事情。