//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