Attempt to read from field 'android.os.MessageQueue android.os.Looper.mQueue' on a null object refer-优快云博客

本文链接：https://blog.youkuaiyun.com/Rodulf/article/details/102399067

在尝试使用子线程的Looper对象创建Handler时，遇到了试图读取null对象上的'MessageQueue'字段的错误。解决方案在于确保正确使用主线程的Looper。参考链接提供了解决此类问题的详情。

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//如果主线程使用了子线程的looper，那么就会报错
mHandler = new Handler(myThread.looper);

Attempt to read from field 'android.os.MessageQueue android.os.Looper.mQueue' on a null object refer

2019-10-08 17:36:39.892 12698-12698/bjpkten.handler E/AndroidRuntime: FATAL EXCEPTION: main
    Process: bjpkten.handler, PID: 12698
    java.lang.RuntimeException: Unable to start activity ComponentInfo{bjpkten.handler/bjpkten.handler.MainActivity}: java.lang.NullPointerException: Attempt to read from field 'android.os.MessageQueue android.os.Looper.mQueue' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6669)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
     Caused by: 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:234)
        at android.os.Handler.<init>(Handler.java:141)
        at bjpkten.handler.MainActivity.onCreate(MainActivity.java:26)
        at android.app.Activity.performCreate(Activity.java:7136)
        at android.app.Activity.performCreate(Activity.java:7127)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:193) 
        at android.app.ActivityThread.main(ActivityThread.java:6669) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

package bjpkten.handler;

import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;

public class MainActivity extends AppCompatActivity {

    private Handler mHandler;
    private Handler mSubHandler;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        MyThread myThread = new MyThread();
        myThread.start();

        Log.d("kodulf-","Looper = " +Looper.getMainLooper());

        //如果主线程使用了子线程的looper，那么就会报错
        mHandler = new Handler(myThread.looper);

        Log.d("kodulf-","mHandler Looper = " +mHandler.getLooper());

        mHandler.sendMessage(new Message());


    }

    class MyThread  extends  Thread{
        Looper looper;
        private Handler childHandler;

        @Override
        public void run() {
            super.run();
            Looper.prepare();
            looper = Looper.myLooper();
            Log.d("kodulf-","MyThread Looper = " +looper);

            childHandler = new Handler(new Handler.Callback() {
                @Override
                public boolean handleMessage(Message msg) {
                    return false;
                }
            });

            looper.loop();
        }
    }
}

参考：http://www.voidcn.com/article/p-wizxvkry-zg.html