Android之view重绘

Android之view重绘

http://qaohao.javaeye.com/blog/478314

 

关键字: android android中实现view的更新有两组方法，一组是invalidate，另一组是postInvalidate，其中前者是在UI线程自身中使用，而后者在非UI线程中使用。
以下是我在android文档中找到的说明，

引用

public void invalidate()
Invalidate the whole view. If the view is visible, onDraw(Canvas) will be called at some point in the future. This must be called from a UI thread. To call from a non-UI thread, call postInvalidate().

public void postInvalidate ()
Cause an invalidate to happen on a subsequent cycle through the event loop. Use this to invalidate the View from a non-UI thread.

google的文档的说明实在是简单，往往看了开发中都会遇到这两个问题:
1. 没有任何异常，view没能刷新。
2. android应用异常终止，打开logcat会看到这样的异常信息, Only the original thread that created a view hierarchy can touch its views。

最后，通过查文档，上网查询才知道，invalidate和postInvalidate方法需要使用android提供的handler,才能 实现重绘，而在文档的说明中却只字不提，真是简单啊。具体是在需要重绘的地方调用handler的sendMessage方法发送消息，紧接着会os会触 发handler中的handlerMessage方法，在handlerMessage方法中再调用view的invalidate或者 postInvalidate方法就能实现重绘。

下面是我分别针对invalidate方法，给出view重绘代码，仅供参考：

class  CustomizeView  extends  WhichView {

    public  CustomizeView(Context context) {
        super (context);
        final  Handler handler =  new  Handler();

        new  Thread( new  Runnable() {
            @Override
            public   void  run() {
                // delay some minutes you desire.
                /*try {
                    Thread.sleep(3000);
                } catch (InterruptedException e) {
                }*/
                handler.post(new  Runnable() {
                    public   void  run() {
                        concreteUpdateUI();
                        invalidate();
                    }
                });
            }
        }).start();
    }

    protected   void  concreteUpdateUI() {
        // Add concrete movement for UI updates.
        // ...
    }
}

class CustomizeView extends WhichView {

	public CustomizeView(Context context) {
		super(context);
		final Handler handler = new Handler();

		new Thread(new Runnable() {
			@Override
			public void run() {
				// delay some minutes you desire.
				/*try {
					Thread.sleep(3000);
				} catch (InterruptedException e) {
				}*/
				handler.post(new Runnable() {
					public void run() {
						concreteUpdateUI();
						invalidate();
					}
				});
			}
		}).start();
	}

	protected void concreteUpdateUI() {
		// Add concrete movement for UI updates.
		// ...
	}
}

或者这样实现也可以。

class  CustomizeView  extends  TextView {

    public  CustomizeView(Context context) {
        super (context);
        new  Thread( new  UIUpdateThread()).start();
    }

    class  UIUpdateThread  implements  Runnable {
        final  Handler mHandler =  new  Handler();

        final  Runnable mUpdateResults =  new  Runnable() {
            public   void  run() {
                concreteUpdateUI();
                invalidate();
            }
        };

        public   void  run() {
            // delay some minutes you desire.
            /*try {
                Thread.sleep(1000 * 5);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }*/
            mHandler.post(mUpdateResults);
        }

    }

    protected   void  concreteUpdateUI() {
        // Add concrete movement for UI updates.
        // ...
    }

}

class CustomizeView extends TextView {

	public CustomizeView(Context context) {
		super(context);
		new Thread(new UIUpdateThread()).start();
	}

	class UIUpdateThread implements Runnable {
		final Handler mHandler = new Handler();

		final Runnable mUpdateResults = new Runnable() {
			public void run() {
				concreteUpdateUI();
				invalidate();
			}
		};

		public void run() {
			// delay some minutes you desire. 
			/*try {
				Thread.sleep(1000 * 5);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}*/
			mHandler.post(mUpdateResults);
		}

	}

	protected void concreteUpdateUI() {
		// Add concrete movement for UI updates.  
		// ...  
	}

}