我编写了一个测试应用程序来了解线程之间的通信机制。
我的来源:
http://techtej.blogspot.de/2011/02/android-passing-data-between-main.html,send message to Thread which is listening for data from network
我不知道如何使用处理程序和Looper。
这里:(每一步都应该给出他的状态:Log.v(TAG,“ ...”))
- MainActivity创建并启动线程(可运行的“ r”)
- MainActivity->消息-> r
- MainActivity
package com.example.desktop.testhandlerlooper;
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 static final String TAG = "MyActivity";
private Handler mHandler2;
private Handler mHandler;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mHandler = new Handler(){
@Override
public void handleMessage(Message msg) {
Log.v(TAG, (String)msg.obj);
}
};
mHandler.post(r);
}
@Override
protected void onStart() {
super.onStart();
for(int i = 10; i>=0; i--)
{
Message msg = mHandler2.obtainMessage();
msg.arg1 = 3;
msg.obj = String.valueOf(i);
mHandler2.sendMessage(msg);
}
}
Runnable r = new Runnable() {
private static final String TAG = "Thread";
@Override
public void run() {
Log.v(TAG, "Before the looper");
Looper.prepare();
//=======================================
mHandler2 = new Handler() {
public void handleMessage(Message msg) {
synchronized (this) {
Message m = mHandler.obtainMessage();
//Message message = Message.obtain();
m.obj = "ACK:" + msg.obj;
Log.v(TAG, (String)m.obj);
//message.sendToTarget();
mHandler.sendMessage(msg);
}
}
};
//=======================================
Looper.loop();
Log.v(TAG, "After the looper");
}
};
}
Logcat:
---------崩溃开始E / AndroidRuntime:致命异常:主要流程:com.example.desktop.testhandlerlooper,PID:2872java.lang.RuntimeException:无法启动活动ComponentInfo {com.example.desktop.testhandlerlooper / com.example.desktop.testhandlerlooper.MainActivity}:java.lang.NullPointerException:尝试调用虚拟方法'null上的'android.os.Message android.os.Handler.obtainMessage()'对象参考在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)在android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)在android.app.ActivityThread.-wrap11(ActivityThread.java)在android.app.ActivityThread $ H.handleMessage(ActivityThread.java:1344)在android.os.Handler.dispatchMessage(Handler.java:102)在android.os.Looper.loop(Looper.java:148)在android.app.ActivityThread.main(ActivityThread.java:5417)在java.lang.reflect.Method.invoke(本机方法)在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:726)在com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)原因:java.lang.NullPointerException:尝试调用虚拟方法'android.os.Message空对象引用上的android.os.Handler.obtainMessage()'在com.example.desktop.testhandlerlooper.MainActivity.onStart(MainActivity.java:35)在android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1237)在android.app.Activity.performStart(Activity.java:6253)在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2379)在android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)在android.app.ActivityThread.-wrap11(ActivityThread.java)在android.app.ActivityThread $ H.handleMessage(ActivityThread.java:1344)在android.os.Handler.dispatchMessage(Handler.java:102)在android.os.Looper.loop(Looper.java:148)在android.app.ActivityThread.main(ActivityThread.java:5417)在java.lang.reflect.Method.invoke(本机方法)在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:726)在com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)申请已终止。
除了我要尝试做的事情之外,我了解该错误,但不知道如何解决。也许MainThread和ChildTread之间都同步?
您正在尝试在初始化之前使用mHandler2变量,如您在日志行中看到的:com.example.desktop.testhandlerlooper.MainActivity.onStart(MainActivity.java:35)