错误：Only the original thread that created a view hierarchy can touch its views——Handler的使用

今天写了一个更新UI的小例子，没想到出了log打印了这样一个错误：Only the original thread that created a view hierarchy can touch its views。goolgle了一下找到了原因。

原来android中相关的view和控件不是线程安全的，我们必须单独做处理。这里借此引出Handler的使用。

 

  Handler的官方描述：

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A Handler allows you to send and process Message and Runnable objects associated with a thread's MessageQueue. Each Handler instance is associated with a single thread and that thread's message queue. When you create a new Handler, it is bound to the thread / message queue of the thread that is creating it -- from that point on, it will deliver messages and runnables to that message queue and execute them as they come out of the message queue

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.Handler的使用场合：

 

1、 to schedule messages and runnables to be executed as some point in the future;

      安排messages和runnables在将来的某个时间点执行。

2、 to enqueue an action to be performed on a different thread than your own.

      将action入队以备在一个不同的线程中执行。即可以实现线程间通信。比如当你创建子线程时，你可以再你的子线程中拿到父线程中创建的Handler对象，就可以通过该对象向父线程的消息队列发送消息了。由于Android要求在UI线程中更新界面，因此，可以通过该方法在其它线程中更新界面。

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通过Handler更新UI实例：

步骤：

1、创建Handler对象（此处创建于主线程中便于更新UI）。

2、构建Runnable对象，在Runnable中更新界面。

3、在子线程的run方法中向UI线程post，runnable对象来更新UI。

 

详细代码如下：

package djx.android;import djx.downLoad.DownFiles;import android.app.Activity;import android.os.Bundle;import android.os.Handler;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.TextView;public class downLoadPractice extends Activity {private Button button_submit=null;private TextView textView=null;private String content=null;private Handler handler=null; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //创建属于主线程的handler handler=new Handler(); button_submit=(Button)findViewById(R.id.button_submit); textView=(TextView)findViewById(R.id.textView); button_submit.setOnClickListener(new submitOnClieckListener()); } //为按钮添加监听器 class submitOnClieckListener implements OnClickListener{@Overridepublic void onClick(View v) {//本地机器部署为服务器，从本地下载a.txt文件内容在textView上显示final DownFiles df=new DownFiles("http://192.168.75.1:8080/downLoadServer/a.txt");textView.setText("正在加载......");new Thread(){public void run(){content=df.downLoadFiles();handler.post(runnableUi); }}.start();} } // 构建Runnable对象，在runnable中更新界面 Runnable runnableUi=new Runnable(){@Overridepublic void run() {//更新界面textView.setText("the Content is:"+content);} }; }

 

 

 

*java线程的详细讲解链接