onDestroy报空指针boolean androidx.fragment.app.FragmentManagerImpl.isDestroyed()' on a null object re...

2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err: java.lang.RuntimeException: Unable to destroy activity {com.leite.app.dayitem/com.leite.app.dayitem.view.user.LoginActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean androidx.fragment.app.FragmentManagerImpl.isDestroyed()' on a null object reference
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:4167)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:4185)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at android.app.ActivityThread.-wrap6(ActivityThread.java)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1521)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at android.os.Handler.dispatchMessage(Handler.java:102)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at android.os.Looper.loop(Looper.java:154)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at android.app.ActivityThread.main(ActivityThread.java:6077)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at java.lang.reflect.Method.invoke(Native Method)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean androidx.fragment.app.FragmentManagerImpl.isDestroyed()' on a null object reference
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at androidx.fragment.app.Fragment.performDetach(Fragment.java:2849)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:1034)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1238)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:1303)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at androidx.fragment.app.FragmentManagerImpl.dispatchStateChange(FragmentManagerImpl.java:2659)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at androidx.fragment.app.FragmentManagerImpl.dispatchDestroy(FragmentManagerImpl.java:2644)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at androidx.fragment.app.FragmentController.dispatchDestroy(FragmentController.java:329)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at androidx.fragment.app.FragmentActivity.onDestroy(FragmentActivity.java:366)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at androidx.appcompat.app.AppCompatActivity.onDestroy(AppCompatActivity.java:233)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at com.leite.app.dayitem.base.BaseActivity.onDestroy(BaseActivity.java:209)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at android.app.Activity.performDestroy(Activity.java:6864)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at android.app.Instrumentation.callActivityOnDestroy(Instrumentation.java:1153)
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:4154)

java.lang.RuntimeException: Unable to destroy activity {com.leite.app.dayitem/com.leite.app.dayitem.view.user.LoginActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean androidx.fragment.app.FragmentManagerImpl.isDestroyed()' on a null object reference
2020-06-08 12:33:57.459 8909-8909/com.leite.app.dayitem W/System.err:     at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:4167)

是因为自己在Fragment重点onDetach增加了如下代码，自己把它设为了空值导致的，新版本的Fragment不会再产生这个问题，可以直接把这部分代码去掉。

  @Override
    public void onDetach() {//避免api bug ：IllegalStateException No activity
        super.onDetach();
        LogUtils.d(TAG, "onDetach");
        try {
            Field childFragmentManager = Fragment.class.getDeclaredField("mChildFragmentManager");
            childFragmentManager.setAccessible(true);
            childFragmentManager.set(this, null);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }