总结Android中多线程更新应用的页面信息的方式

一、runOnUiThread的用法
runOnUiThread是Activity的内部方法，使用时最好指定当前的环境变量（Context）。

new Thread(new Runnable() {

    @Override
    public void run() {
      runOnUiThread(new Runnable() {
        public void run() {
          Toast.makeText(mainActivity.this,"UI操作。。。",0).show();
        }
      });

    }
  }).start();

执行runOnUiThread这个方法会调用父类中的

public final void runOnUiThread(Runnable action){
 if(Thread.currentThread()!=mUiThread){
 mHandler.post(action);
 }else{
  action.run();
 }
}

二、新线程中View直接在UI线程中更新的方法

textView.postDelayed(new Runnable() {

    @Override
    public void run() {
      textView.setText("Test View.post(Runnable)");

    }
  }, 1000);
-

 textView.post(new Runnable() {

    @Override
    public void run() {
      textView.setText("Test View.postDelay(Runnable，long)");

    }
  });

三、Handler(消息传递机制)使用

Handler myHandler = new Handler(){
 public void handleMessage(Message msg){
  super.handleMessage(msg);
  }
};

也可以继承handler

class MyHandler extends handler{
  public MyHandler(){

 }
 @Override
 public void handleMessage(Message msg){
  super.handleMessage(msg);
 }
}

分发Message或者Runnable对象到handler所在的线程中一般handler在主线程中。

handler中一些分发消息的方法：

• post（Runnable）
• postAtTime(Runnable,long)
• postDelay(Runnable,long)
• sendEmptyMessage(int what)
• sendMessage(Message)
• senMessageAtTime(Message，long)
• sendMessageDelayed(Message,long)

post方式添加一个实现Runnable接口的匿名对象到消息对列中，在目标收到消息后就可以以回调的方式在自己的线程中执行

Message对象所具有的属性：

Message message = Message.obtain();
message.arg1 = 1;
message.arg2 = 2;
message.obj = "Demo";
message.what = 3;
Bundle bundle = new Bundle();
bundle.putString( "name","Lucy");
message.setData(bundle);

下面贴上一段示例代码（开启新线程实现电子广告牌）

public class MainActivity extends Activity implements Runnable {

  private ImageView iv;
  private TextView tv;

  private Handler handler;
  private int[] path = new int[]{R.drawable.img01,R.drawable.img02,R.drawable.img03,R.drawable.img04,
      R.drawable.img05,R.drawable.img06};
  private String[] title = new String[]{"编程词典系列","高效开发","快乐分享","用户人群","快速学习","全方位查询"};
  private int index =0;
  @Override
  protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    iv = (ImageView) findViewById(R.id.imageView1);
    tv = (TextView) findViewById(R.id.textView1);

    Thread t = new Thread(this);
    t.start();
    handler = new Handler(){
      public void handleMessage(Message msg){
        if (msg.what ==1) {
          tv.setText(msg.getData().getString("title"));
          iv.setImageResource(path[msg.arg1]);
        }
        super.handleMessage(msg);
      }
    };

  }

  @Override
  public void run() {

    while(!Thread.currentThread().isInterrupted()){
      index = new Random().nextInt(path.length);
      Message m = handler.obtainMessage();
      m.arg1 = index;
      Bundle bundle = new Bundle();
      m.what = 1;
      bundle.putString("title", title[index]);
      m.setData(bundle);
      handler.sendMessage(m);
      try {
        Thread.sleep(2000);
      } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
      }
    }    

  }

  }

四、AsyncTask异步任务的用法

• AsyncTask实际上是一个线程池，在代码上比handler要轻量级但是实际上要比Handler要耗资源，Handler仅仅发送了一个消息队列，连线程池对没有开。
• onPreExecute()，（可选方法）最新用户调用excute时的接口，任务执行之前调用该方法，可以在这里显示进度对话框。
• doInBackground(Params...),后台执行比较好使的操作，不能直接操纵UI。在该方法中使用publishProgress（progress...）来更新任务的进度。
• onProgressUpdate(Progress...),在主线程中执行，显示进度条
• onPostExecute(Result),此方法可以从doinbackground得到的结果来操作UI，在主线程中执行，执行的结果作为参数返回。
• onCancelled(Object)调用此方法可以随时取消操作。

AsyncTask定义的三种泛型

• params: 启动任务执行的输入参数，如：http请求的URL
• progress:后台任务执行的百分比
• result:返回结果，如：String、list集合等

 private class MyTask extends AsyncTask<params, progress, result> { ... }

示例代码：

  private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {
   protected Long doInBackground(URL... urls) {
     int count = urls.length;
     long totalSize = 0;
     for (int i = 0; i < count; i++) {
       totalSize += Downloader.downloadFile(urls[i]);
       publishProgress((int) ((i / (float) count) * 100));
       // Escape early if cancel() is called
       if (isCancelled()) break;
     }
     return totalSize;
   }

   protected void onProgressUpdate(Integer... progress) {
     setProgressPercent(progress[0]);
   }

   protected void onPostExecute(Long result) {
     showDialog("Downloaded " + result + " bytes");
   }
  }

获取网络图片的示例代码：

 public class MainActivity extends ActionBarActivity {
  private ImageView iv;
  private Button bt;
  private String imagePath = "http://192.168.1.1/sa";
  private ProgressDialog dialog;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    iv = (ImageView) findViewById(R.id.imageView1);
    bt = (Button) findViewById(R.id.button1);
    dialog = new ProgressDialog(this);
    dialog.setTitle("提示信息：");
    dialog.setMessage("正在下载。。。");
    bt.setOnClickListener(new OnClickListener() {

      @Override
      public void onClick(View v) {
        new MyTask().execute(imagePath);

      }
    });
  }
  public class MyTask extends AsyncTask<String, Void, Bitmap>{

    @Override
    protected Bitmap doInBackground(String... params) {
      HttpClient httpClient = new DefaultHttpClient();
      HttpGet httpGet = new HttpGet(params[0]);
      Bitmap bitmap = null;
      try {
        HttpResponse httpResponse = httpClient.execute(httpGet);
        if (httpResponse.getStatusLine().getStatusCode()==200) {
          HttpEntity httpEntity = httpResponse.getEntity();
          byte[] data = EntityUtils.toByteArray(httpEntity);
          bitmap= BitmapFactory.decodeByteArray(data, 0, data.length);
        }
      } catch (Exception e) {

        e.printStackTrace();
      }

      return bitmap;
    }

    @Override
    protected void onPreExecute() {
      super.onPreExecute();
      dialog.show();
    }

    @Override
    protected void onPostExecute(Bitmap result) {
      super.onPostExecute(result);
      iv.setImageBitmap(result);
      dialog.dismiss();
    }
   }
  }