解决 Attempt to read from field ‘android.os.MessageQueue android.os.Looper.mQueue‘ on a null object ..

异常信息

java.lang.NullPointerException: Attempt to read from field 'android.os.MessageQueue android.os.Looper.mQueue' on a null object reference
at android.os.Handler.<init>(Handler.java:257)
at android.os.Handler.<init>(Handler.java:162)
at com.zlgspace.andcodec.camera.CameraWrapper.<init>(CameraWrapper.java:60)
at com.zlgspace.andcodec.MainActivity$1.onClick(MainActivity.java:36)
at android.view.View.performClick(View.java:7464)
at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:1213)
at android.view.View.performClickInternal(View.java:7441)
at android.view.View.access$3700(View.java:835)
at android.view.View$PerformClick.run(View.java:28825)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loopOnce(Looper.java:201)
at android.os.Looper.loop(Looper.java:288)
at android.app.ActivityThread.main(ActivityThread.java:7870)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)   

异常原因

因为Handler传入的Looper为null导致，一般应该是HandlerThread创建后没有调用start(),直接getLooper()创建Handler导致。

解决办法

解决也很简单，保证创建Handler时传的Looper不为空即可，比如HandlerThread必须先调用start()，之后再通过getLooper()创建Handler。