线程更新UI



        项目中我们为了避免不阻碍UI线程，进程会创建另外的线程来执行操作，在android中有两种实现线程thread的方法：一种就是继承Thread类，一种是实现Runnable接口
使用线程我们就离不开Handler。

在一个线程中更新UI，我们都知道handler + thread 代码如下：

public class MainActivity extends Activity {  
    private EditmText mText;  
    private Button mButton;  
    private myHandler handler;  
    
    @Override  
    public void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.activity_main);  
        mText = (EditmText)findViewById(R.id.ui_txt);  
        mButton = (Button)findViewById(R.id.update_ui_btn);  
        mButton.setOnClickListener(new View.OnClickListener() {  
                
            public void onClick(View v) {  
                handler = new myHandler();  
                myThread thread = new myThread();  
                thread.start();  
            }  
        });  
    }  
    
 
    private class myHandler extends Handler{  
        @Override  
        public void handleMessage(Message msg) {            
            super.handleMessage(msg);  
            Bundle bundle = msg.getData();  
            String str = bundle.getString("str");  
            mText.setmText(str);  
        }  
    }  
    private class myThread extends Thread{  
        @Override  
        public void run() {  
            try {  
                Thread.sleep(2000);  
            } catch (InterruptedException e) {  
                e.printStackTrace();  
            }  
            Message msg = new Message();  
            Bundle bundle = new Bundle();  
            bundle.putString("str", "名字");  
            msg.setData(bundle);  
            MainActivity.this.myHandler.sendMessage(msg);  
                
        }  
    }  
}

上面是继承Thread类来创建线程，我们也可以实现Runnable接口

public class MainActivity extends Activity {  
    private EditmText mText;  
    private Button mButton;        
    
    @Override  
    public void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.activity_main);  
        mText = (EditmText)findViewById(R.id.ui_txt);  
        mButton = (Button)findViewById(R.id.update_ui_btn);  
        mButton.setOnClickListener(new View.OnClickListener() {  
                
            public void onClick(View v) {                                           
                thread.start();  
            }  
        });  		
    }  
	
	public Handler handler = new Handler(){   
        @Override  
        public void handleMessage(Message msg) {            
            super.handleMessage(msg);  
            Bundle bundle = msg.getData();  
            String str = bundle.getString("str");  
            mText.setmText(str);  
        }      
    }
 
   
    final Thread thread = new Thread(new Runnable(){ 
        @Override  
        public void run() {  
            try {  
                Thread.sleep(2000);  
            } catch (InterruptedException e) {  
                e.printStackTrace();  
            }  
            Message msg = new Message();  
            Bundle bundle = new Bundle();  
            bundle.putString("str", "名字");  
            msg.setData(bundle);  
            handler.sendMessage(msg);  
                
        }  
    }  
}

有时候我们在项目中经常用到计时器。代码如下：

public class MainActivity extends ActionBarActivity {
	private TextView mTime;
	private Button mStart;
	private int cunt;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();
    }
	private void initView() {
		mTime = (TextView) findViewById(R.id.main_text);
		mStart = (Button) findViewById(R.id.main_bt);
		mStart.setOnClickListener(new OnClickListener() {
			
			@Override
			public void onClick(View arg0) {
				//将线程添加到队列里
				handler.post(updateThread);  
			}
		});
	}  
	//创建一个Handler对象  
	Handler handler  = new Handler();  
	//将要执行的操作写在线程对象的run方法当中  
	Runnable updateThread =  new Runnable(){  
		@Override 
		public void run() {
			if(cunt < 100){
				cunt++;
				mTime.setText(cunt + "s");
				//在run方法内部，执行postDelayed或者是post方法  
				handler.postDelayed(updateThread, 500);  
			}
		}           
	};  
}

还有runOnUiThread(Runnable)更新UI，我们都知道AsyncTask中的onPostExecute方法中可以更新UI,但是有时候我们要在doInBackground方法中更新UI，我们就可以使用runOnUiThread(Runnable)来更新UI
代码如下：

class saveVideoTask extends AsyncTask<String, Integer, Boolean>{
		
		@Override
		protected void onPreExecute() {
			super.onPreExecute();			
		}
		@Override
		protected Boolean doInBackground(String... params) {
			//runOnUiThread(Runnable)(runOnUiThread是Activity中的方法，在线程中我们需要告诉系统是哪个activity调用，所以前面显                         // 示的指明了activity。)
			Activity.this. runOnUiThread(new Runnable() {
				@Override
				public void run() {
					//更新UI操作
				}

			});
			
			return null;
		}
		
		@Override
		protected void onPostExecute(Boolean result) {
			super.onPostExecute(result);			
		}
	}