Android fragment 事务 - 替换 fragment 会使旧 fragment 处于奇怪状态

Question

我有奇怪的行为。每次我在 Activity 中替换相同类型的 fragment (使用事务)时，新的 Fragment 实例都会添加到 Fragment List 中。旧实例在 fragment 管理器中保持 Activity 状态，并且在方向更改后在屏幕上可见(尽管不可点击)。

我的 Activity 布局:

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

-->

<!-- A DrawerLayout is intended to be used as the top-level content view using match_parent for both width and height to consume the full space available. -->

<android.support.v4.widget.DrawerLayout
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.cubesoft.zenfolio.moments.app.activity.MainActivity" >

    <FrameLayout
        android:id="@+id/container"
        android:layout_width="match_parent"
        android:layout_height="match_parent" >
    </FrameLayout>

    <fragment
        android:id="@+id/navigation_drawer"
        android:name="com.cubesoft.zenfolio.moments.app.fragment.NavigationDrawerFragment"
        android:layout_width="@dimen/navigation_drawer_width"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        tools:layout="@layout/fragment_navigation_drawer" />
</android.support.v4.widget.DrawerLayout>

<fragment
    android:id="@+id/fragmentConnectionStatus"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    class="com.cubesoft.zenfolio.fragment.ConnectionStatusFragment" />

我的改变 fragment 的代码:

@Override
public void onNavigationDrawerItemSelected(int position) {
    mCurrentDrawerPosition = position;
    // update the main content by replacing fragments


    List<Fragment> fragmemts = getSupportFragmentManager().getFragments();

    switch (position) {
    case 0:{
        if ( getMyApplication().getGroupModel().getUsersCount() > 0  ) {
            final Fragment fragment = UserSelectionFragment.newInstance();

            final FragmentManager fragmentManager = getSupportFragmentManager();
            //fragmentManager.popBackStack();
            final FragmentTransaction tr = fragmentManager
                    .beginTransaction();

            tr.replace(R.id.container, fragment);
            tr.addToBackStack(null);
            tr.setCustomAnimations(R.anim.abc_fade_in, R.anim.abc_fade_out);
            tr.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
            tr.commit();

        } else {
            final Fragment fragment = MomentsFragment.newInstance(mUsername);

            final FragmentManager fragmentManager = getSupportFragmentManager();
            //fragmentManager.popBackStack();

            final FragmentTransaction tr = fragmentManager
                    .beginTransaction();
            tr.replace(R.id.container, fragment);
            //tr.setCustomAnimations(R.anim.abc_fade_in, R.anim.abc_fade_out);
            tr.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
            tr.addToBackStack(null);

            tr.commit();
        }





        break;
    }

    case 1: {
        final Fragment fragment = DownloadFragment.newInstance();
        final FragmentManager fragmentManager = getSupportFragmentManager();
        //fragmentManager.popBackStack();
        final FragmentTransaction tr = fragmentManager
                .beginTransaction();
        tr.replace(R.id.container, fragment);
        tr.addToBackStack(null);

        tr.commit();
        break;
    }

    /*case 2:
        fragment = UserSelectionFragment.newInstance();
        break;*/

    }


}

---

UserSelectionFragment 在几次方向更改后显示不正确，UserSelectionFragment 的旧实例保留在 Fragment List 中，但它们的 View 对象为空。

怎么了？

Answer 1

尝试删除

 tr.addToBackStack(null);

对我来说，这会将您的 fragment 添加到后台堆栈，这就是将它们保留在您的 fragment 列表中的原因。它们的 View 为空，因为它们在进入背景之前已被销毁。