Android开发之handler(三)handler真的是重新启动一个线程吗?
2015-06-22 11:36
501 查看
在handler(二)中点击打开链接,我们说handler是开启了另外一个线程,而且看代码的话确实是这样,实现了runnable接口,这在java中就是开启了一个线程,但是情况中的是这样吗?我们不妨来做个试验,如下
[java] view
plaincopy
<span style="font-size:14px;">package com.handlerThread;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
public class handlerThread extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Handler handler = new Handler();
handler.post(r);
System.out.println("activity线程ID:"+Thread.currentThread().getId());
System.out.println("activity线程name:"+Thread.currentThread().getName());
}
Runnable r = new Runnable(){
@Override
public void run() {
// TODO Auto-generated method stub
System.out.println("handler线程ID:"+Thread.currentThread().getId());
System.out.println("handler线程name:"+Thread.currentThread().getName());
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
}</span>
运行结果
![](http://img.my.csdn.net/uploads/201211/17/1353149722_5293.png)
其实,当我看到这里的时候也不敢相信,但是事实就是这样,handler没有重新开启一个线程,而是跟activity在同一个线程里,但是这种写法也就非常接近java的标准线程的写法了,难怪会误导人,如下是java的标准线程写法。
[java] view
plaincopy
<span style="font-size:14px;">package com.handlerThread;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
public class handlerThread extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// Handler handler = new Handler();
// handler.post(r);
Thread t = new Thread(r);
t.start();
System.out.println("activity线程ID:"+Thread.currentThread().getId());
System.out.println("activity线程name:"+Thread.currentThread().getName());
}
Runnable r = new Runnable(){
@Override
public void run() {
// TODO Auto-generated method stub
System.out.println("handler线程ID:"+Thread.currentThread().getId());
System.out.println("handler线程name:"+Thread.currentThread().getName());
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
}</span>
运行结果如下:
![](http://img.my.csdn.net/uploads/201211/17/1353150398_4103.png)
这里就才是我们这种想要的结果,两者比较我们就会发现,handler虽然实现了runnable接口,但是却并没有启动一个线程,而是直接调用run方法。那andriod为什么要这样设计呢,既然不启动新的线程,为什么还要多此一举来实现runnable接口呢,我们继续探讨,下次再说。
[java] view
plaincopy
<span style="font-size:14px;">package com.handlerThread;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
public class handlerThread extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Handler handler = new Handler();
handler.post(r);
System.out.println("activity线程ID:"+Thread.currentThread().getId());
System.out.println("activity线程name:"+Thread.currentThread().getName());
}
Runnable r = new Runnable(){
@Override
public void run() {
// TODO Auto-generated method stub
System.out.println("handler线程ID:"+Thread.currentThread().getId());
System.out.println("handler线程name:"+Thread.currentThread().getName());
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
}</span>
运行结果
![](http://img.my.csdn.net/uploads/201211/17/1353149722_5293.png)
其实,当我看到这里的时候也不敢相信,但是事实就是这样,handler没有重新开启一个线程,而是跟activity在同一个线程里,但是这种写法也就非常接近java的标准线程的写法了,难怪会误导人,如下是java的标准线程写法。
[java] view
plaincopy
<span style="font-size:14px;">package com.handlerThread;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
public class handlerThread extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// Handler handler = new Handler();
// handler.post(r);
Thread t = new Thread(r);
t.start();
System.out.println("activity线程ID:"+Thread.currentThread().getId());
System.out.println("activity线程name:"+Thread.currentThread().getName());
}
Runnable r = new Runnable(){
@Override
public void run() {
// TODO Auto-generated method stub
System.out.println("handler线程ID:"+Thread.currentThread().getId());
System.out.println("handler线程name:"+Thread.currentThread().getName());
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
}</span>
运行结果如下:
![](http://img.my.csdn.net/uploads/201211/17/1353150398_4103.png)
这里就才是我们这种想要的结果,两者比较我们就会发现,handler虽然实现了runnable接口,但是却并没有启动一个线程,而是直接调用run方法。那andriod为什么要这样设计呢,既然不启动新的线程,为什么还要多此一举来实现runnable接口呢,我们继续探讨,下次再说。
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