UI更新方法Handler和runOnUiThread

UI更新问题：

在多线程进行UI更新时候报错android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.

分析：

在Android平台下，进行多线程编程时，经常需要在主线程之外的一个单独的线程中进行某些处理，然后更新用户界面显示。但是，在主线线程之外的线程中直接更新页面显示的问题是

报异常：android.view.ViewRoot$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.

【只有原始创建这个视图层次(view hierachy)的线程才能修改它的视图(view)】

UI更新解决方法：

也就是说必须在一般必须在程序的主线程(也就是ui)线程中进行更新界面显示的工作。可以采用下面的方法之一来解决：

方法一

在onCreate方法中创建一个Handler实例，或者在主线程中创建一个Handler实例，UI刷新的程序放到这个Hanlder实例中执行，如下

public class MainActivity extends Activity {

	private ImageView imageView;
	private Button button;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		button = (Button)this.findViewById(R.id.button);
		imageView = (ImageView)this.findViewById(R.id.imageview);
		button.setOnClickListener(new View.OnClickListener() {
			@Override
			public void onClick(View v) {
				try {
					new Thread(){
						public void run()
						{
							try {
								InputStream is = HttpUtils.getImageViewInputSream();
								if(is!=null)
								{
									Bitmap  bitmap = BitmapFactory.decodeStream(is);
									Message msg = new Message();
									msg.what = 1;
									Bundle bundle = new Bundle();
									bundle.putParcelable("bm", bitmap);
									msg.setData(bundle);
									handler.sendMessage(msg);
								}
							} catch (Exception e) {
								e.printStackTrace();
							}
						}
					}.start();
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		});
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}

	@Override
	public boolean onOptionsItemSelected(MenuItem item) {
		int id = item.getItemId();
		if (id == R.id.action_settings) {
			return true;
		}
		return super.onOptionsItemSelected(item);
	}
	
	Handler handler = new Handler() {
		@Override
		public void handleMessage(Message msg) {
			super.handleMessage(msg);
			int what = msg.what;
			switch (what) {
			case 1:
				Bundle bundle = msg.getData();
				Bitmap bitmap = (Bitmap)bundle.getParcelable("bm");
				imageView.setImageBitmap(bitmap);
				break;
			default:
				break;
			}

		}
	};
}

方法二

利用Activity.runOnUiThread（Runnable）把更新UI的代码，创建在Runable中，然后更新UI时，将这个Runable对象传递给Activity.runOnUiThread（Runnable）。这样Runnable对象就能在UI程序中被调用

public class MainActivity extends Activity {
	private ImageView imageView;
	private Button button;
	private Bitmap  bitmap;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		button = (Button)this.findViewById(R.id.button);
		imageView = (ImageView)this.findViewById(R.id.imageview);
		button.setOnClickListener(new View.OnClickListener() {
			@Override
			public void onClick(View v) {
				try {
					new Thread(){
						public void run() {
							InputStream is = HttpUtils.getImageViewInputSream();
							bitmap = BitmapFactory.decodeStream(is);
							if(bitmap!=null)
							{
								MainActivity.this.runOnUiThread(new Runnable() {
									@Override
									public void run() {
										imageView.setImageBitmap(bitmap);
									}
								});
							}
						}
					}.start();
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		});
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}

	@Override
	public boolean onOptionsItemSelected(MenuItem item) {
		int id = item.getItemId();
		if (id == R.id.action_settings) {
			return true;
		}
		return super.onOptionsItemSelected(item);
	}
}