当我添加片段自定义转换时,单元测试NPE

Question

当我添加自定义转换时,OnBackPressed()测试会抛出NPE .没有自定义过渡就没问题.为什么？

这个NPE只能在单元测试中发生,而不是应用程序.

 class MyActivity {
    @Override
    public void onBackPressed() {
        .......
        super.onBackPressed();
    }

    private void putFragment(Fragment fragment) {
            String tag = fragment.getClass().getName();

            FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();

            // TEST FAILED IF I ADD THE FOLLOWING LINE
            transaction.setCustomAnimations(
                    R.anim.slide_in_left_fade_in,
                    R.anim.fade_out_short_anim_time,
                    R.anim.fade_in_short_anim_time,
                    R.anim.slide_out_right_fade_out);

            transaction.replace(R.id.ub__add_profiles_content, fragment, tag);
            transaction.addToBackStack(tag);
            transaction.commit();
    }
}

class MyActivityTest extends RiderRobolectricBase {

    @Test
    public void onBackPressed() {
       putFragment(someFragment);

       mMyActivity.onBackPressed();
    }
}

例外:

java.lang.NullPointerException
    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1126)
    at android.support.v4.app.FragmentManagerImpl.removeFragment(FragmentManager.java:1304)
    at android.support.v4.app.BackStackRecord.popFromBackStack(BackStackRecord.java:909)
    at android.support.v4.app.FragmentManagerImpl.popBackStackState(FragmentManager.java:1625)
    at android.support.v4.app.FragmentManagerImpl.popBackStackImmediate(FragmentManager.java:561)
    at android.support.v4.app.FragmentActivity.onBackPressed(FragmentActivity.java:166)
    at MyActivity.onBackPressed(MyActivity.java:28)

Answer 1

Onbackpress，您将从后退堆栈中反转之前的步骤。第一个是删除现有的片段。该片段已与活动分离，并且
您不会保留该片段的实例。

java.lang.NullPointerException
    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1126)
    at android.support.v4.app.FragmentManagerImpl.removeFragment(FragmentManager.java:1304)
    at android.support.v4.app.BackStackRecord.popFromBackStack(BackStackRecord.java:909)
    at android.support.v4.app.FragmentManagerImpl.popBackStackState(FragmentManager.java:1625)
    at android.support.v4.app.FragmentManagerImpl.popBackStackImmediate(FragmentManager.java:561)
    at android.support.v4.app.FragmentActivity.onBackPressed(FragmentActivity.java:166)
    at MyActivity.onBackPressed(MyActivity.java:28)

你接电话putFragment(someFragment)。
所以当你去调用setCustomAnimations时。前一个视图不会保存以供在转换中使用。

// TEST FAILED IF I ADD THE FOLLOWING LINE
transaction.setCustomAnimations(
    R.anim.slide_in_left_fade_in,
    R.anim.fade_out_short_anim_time,
    R.anim.fade_in_short_anim_time,
    R.anim.slide_out_right_fade_out);

您可以在片段的 oncreate 方法中保留该实例：

setRetainInstance(true);

至于这在您的应用程序中的工作，我看不到您的 Activity 的 onBackPressed 事件中的代码。