片段交易

Question

在我的主要活动中，我有这一行用viewgroup

替换片段

MainActivity：

public class ActivityMain extends AppCompatActivity {
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        getSupportFragmentManager().beginTransaction()
                .replace(R.id.activity_main_container, new HomeFragment())
                .setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN)
                .addToBackStack(null)
                .commit();
    }
}

活动布局：

<android.support.design.widget.CoordinatorLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <FrameLayout
        android:id="@+id/activity_main_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:clickable="true"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"/>

</android.support.design.widget.CoordinatorLayout>

我的HomeFragment是：

public class HomeFragment extends Fragment {

    public HomeFragment() {

    }

    @Override
    public void onCreate(Bundle saved) {
        super.onCreate(saved);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_test, container, false);
        Log.e("HomeFragment", " onCreateView");
        return view;
    }
}

现在在构建应用程序并在模拟器上运行后，我的代码运行重复HomeFragment，我该如何阻止此操作？

Answer 1

框架将在活动恢复时恢复您的片段状态，例如在配置更改后。您应该只在第一次创建活动时操作片段。

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    if(savedInstanceState == null) {
        // set up your fragments
    }  
}

Answer 2

  

如果片段已经启动，请执行此操作   再次

private Class mFragmentClass; mFragmentClass = InfoFragment.class; 
if (null != mFragmentClass) { 
try { 
mFragment = (Fragment) mFragmentClass.newInstance();
if(mFragment instanceof (Fragment)mFragmentClass){
 FragmentManager fragmentManager = getSupportFragmentManager(); fragmentManager.beginTransaction().replace(R.id.content_navigation_menu, mFragment).commit(); 
} catch (InstantiationException exception) { exception.printStackTrace();
 } catch (IllegalAccessException exception) { exception.printStackTrace(); }
}else {
//do nothing
}