问题1：反射获取Application对象

1.作为一种新的思路，获取Application，确实是一种拓展，但是使用反射获取ActivityThread，未来会不会触发Android 9.0 之后的反射限制。

2.在ActivityThread中，看到currentApplication()方法上面的注解

@UnsupportedAppUsage 

我觉得这种方式还是没有将Application-onCreate（）作为静态变量保存，然后全局获取更好。

问题2：Demo在内存不足时，App被杀死，进行内容重启时，会闪退。

因为我刚开始进入课程学习阶段，解决起来，有点没有头绪，需要老师帮忙看一下

 Caused by: android.view.InflateException: Binary XML file line #9: Binary XML file line #9: Error inflating class fragment
     Caused by: android.view.InflateException: Binary XML file line #9: Error inflating class fragment
     Caused by: java.lang.IllegalStateException: Fragment com.mooc.libcommon.view.WindowInsetsNavHostFragment did not create a view.
        at androidx.fragment.app.FragmentManagerImpl.onCreateView(FragmentManagerImpl.java:3234)
        at androidx.fragment.app.FragmentController.onCreateView(FragmentController.java:134)
        at androidx.fragment.app.FragmentActivity.dispatchFragmentsOnCreateView(FragmentActivity.java:357)
        at androidx.fragment.app.FragmentActivity.onCreateView(FragmentActivity.java:336)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:784)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:734)
        at android.view.LayoutInflater.rInflate(LayoutInflater.java:867)
        at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:828)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:519)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:427)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:374)
        at androidx.appcompat.app.AppCompatDelegateImpl.setContentView(AppCompatDelegateImpl.java:555)
        at androidx.appcompat.app.AppCompatActivity.setContentView(AppCompatActivity.java:161)
        at com.mooc.ppjoke.MainActivity.onCreate(MainActivity.java:58)
        at android.app.Activity.performCreate(Activity.java:7101)
        at android.app.Activity.performCreate(Activity.java:7092)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1215)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2763)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2888)
        at android.app.ActivityThread.-wrap11(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1609)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6606)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:518)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:821)