/********************************************************************************************
* author：conowen@大鐘?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
* E-mail：conowen@hotmail.com????????????????????????????????????????????????????????????????????????????????????????????????????????????
* http://blog.csdn.net/conowen ????????????????????????????????????????????????????????????????????????????????????????????????????????????
* 注：本文為原創，僅作為學習交流使用，轉載請標明作者及出處。?????

http://blog.csdn.net/conowen/article/details/7843487

********************************************************************************************/

1、View

View extends Object implements Drawable.Callback KeyEvent.Callback AccessibilityEventSource java.lang.Object ?? ? android.view.View Known Direct Subclasses（直接子類，SurfaceView是View的子類） AnalogClock,ImageView,KeyboardView,MediaRouteButton,ProgressBar,Space,SurfaceView,TextView,TextureView,ViewGroup,ViewStub Known Indirect Subclasses（間接子類） AbsListView,AbsSeekBar,AbsSpinner,AbsoluteLayout,AdapterView<T extends Adapter>,AdapterViewAnimator,AdapterViewFlipper,AppWidgetHostView,AutoCompleteTextView,Button,CalendarView, CheckBox, CheckedTextView, Chronometer, and 53 others. Class Overview This class represents the basic building block for user interface components. A View occupies a rectangular area on the screen and is responsible for drawing and event handling. View is the base class forwidgets, which are used to create interactive UI components (buttons, text fields, etc.). TheViewGroup subclass is the base class forlayouts, which are invisible containers that hold other Views (or other ViewGroups) and define their layout properties. View類為用戶界面提供了最基礎的組件，View類組件負責更換屏幕與處理事件。同時，View類也是widgets類的基礎類，widgets類可以創建基礎的UI組件，如Bottons、Textview等等。View類的其中一個直接子類ViewGroup是layous的基礎類，layous是用來裝載View或者其他的ViewGrous的，并且可以定義這些裝載內容的特性。

2、

????????? 從上述的Overview可知，SurfaceView是繼承于View類的，（GLSurfaceView是繼承于SurfaceView的）。關于SurfaceView的詳細可以參看之前的博文

http://blog.csdn.net/conowen/article/details/7821409

Android更新屏幕主要有兩種方式，繼承SurfaceView實現SurfaceHolder.callback接口來實現屏幕的更新。

或者直接繼承View類，復寫OnDraw方法實現更新屏幕。

事實上，兩種是用本質的區別的。

3、View與SurfaceView更新屏幕的區別

對于SurfaceView更新屏幕，是在非UI線程（主線程）中更新的。而對于View，則是在UI的主線程中更新畫面。
那在UI的主線程中更新畫面很容易造成主線程的堵塞，造成程序的長時間無響應，當主UI線程超過5秒鐘沒有響應用戶的操作，Android系統會提示是否關閉應用程序。

當使用SurfaceView 來更新畫面的話，就不必擔心堵塞主UI線程這個問題了。但是這也帶來了另外一個問題，線程的同步性。

所以當更新操作說花的時間較長，而且數據量較大的話，一般采用SurfaceView方式更新屏幕，而少用View。

4、Demo程序

[java] view plaincopyprint?

/*

* author: conowen

* e-mail: conowen@hotmail.com

* date? :? 2012.8.8

*/?

package com.conowen.viewtestdemo;?

?

import android.content.Context;?

import android.graphics.Canvas;?

import android.graphics.Color;?

import android.graphics.Paint;?

import android.graphics.RectF;?

import android.view.View;?

?

public class MyView extends View {?

?

??? private int counter;?

?

??? public MyView(Context context) {?

??????? super(context);?

??????? // TODO Auto-generated constructor stub?

??? }?

?

??? @Override?

??? protected void onDraw(Canvas canvas) {?

??????? // TODO Auto-generated method stub?

??????? super.onDraw(canvas);?

/*????? synchronized (this) {

??????????? try {

??????????????? wait(10 * 1000);

??????????? } catch (InterruptedException e) {

??????????????? // TODO Auto-generated catch block

??????????????? e.printStackTrace();

??????????? }

??????? }

*/?

??????? // 設定Canvas對象的背景顏色?

??????? canvas.drawColor(Color.YELLOW - counter);?

?

??????? // 創建畫筆?

??????? Paint p = new Paint();?

??????? // 設置畫筆顏色?

??????? p.setColor(Color.RED);?

??????? // 設置文字大小?

??????? p.setTextSize(40);?

??????? // 消除鋸齒?

??????? p.setFlags(Paint.ANTI_ALIAS_FLAG);?

?

??????? // 在canvas上繪制rect?

??????? canvas.drawArc(new RectF(100, 50, 400, 350), 0, counter, true, p);?

??????? if (counter == 400) {?

??????????? counter = 0;?

??????? }?

?

??????? canvas.drawText("counter = " + (counter++), 500, 200, p);?

??????? // 重繪, 再一次執行onDraw 程序?

??????? invalidate();?

?

??? }?

?

}?

/** author: conowen* e-mail: conowen@hotmail.com* date : 2012.8.8*/ package com.conowen.viewtestdemo;import android.content.Context; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import android.graphics.RectF; import android.view.View;public class MyView extends View {private int counter;public MyView(Context context) {super(context);// TODO Auto-generated constructor stub}@Overrideprotected void onDraw(Canvas canvas) {// TODO Auto-generated method stubsuper.onDraw(canvas); /* synchronized (this) {try {wait(10 * 1000);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}} */// 設定Canvas對象的背景顏色canvas.drawColor(Color.YELLOW - counter);// 創建畫筆Paint p = new Paint();// 設置畫筆顏色p.setColor(Color.RED);// 設置文字大小p.setTextSize(40);// 消除鋸齒p.setFlags(Paint.ANTI_ALIAS_FLAG);// 在canvas上繪制rectcanvas.drawArc(new RectF(100, 50, 400, 350), 0, counter, true, p);if (counter == 400) {counter = 0;}canvas.drawText("counter = " + (counter++), 500, 200, p);// 重繪, 再一次執行onDraw 程序invalidate();}}
效果圖：

打開下面的代碼，測試堵塞主UI線程（長按屏幕5秒以上）就會出現如下的圖。

[java] view plaincopyprint?

synchronized (this) {?

??????????? try {?

??????????????? wait(10 * 1000);?

??????????? } catch (InterruptedException e) {?

??????????????? // TODO Auto-generated catch block?

??????????????? e.printStackTrace();?

??????????? }?

??????? }?

synchronized (this) {try {wait(10 * 1000);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}}

注意：

???? onDraw方法是運行于主UI線程中的，如果你在onDraw中執行invalidate()方法去更新屏幕，是可以的。但是你既要繼承View而且要不希望堵塞主UI線程的話，可以另外新建線程，然后在線程中執行postInvalidate()方法去更新屏幕。也就是說invalidate()方法只能在主UI線程中被調用，postInvalidate()方法只能在非主UI線程中被調用。否則會出現如下error

08-08 15:33:34.587: E/AndroidRuntime(4995): android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.

這兩個方法只是再次調用onDraw方法而已。

Invalidate the whole view. If the view is visible, onDraw(android.graphics.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().

如下面的代碼所示。這樣的話，就不必擔心主UI線程被堵塞了。

[java] view plaincopyprint?

/*

* author: conowen

* e-mail: conowen@hotmail.com

* date? :? 2012.8.4

*/?

package com.conowen.viewtestdemo;?

?

import java.util.Timer;?

import java.util.TimerTask;?

?

import android.content.Context;?

import android.graphics.Canvas;?

import android.graphics.Color;?

import android.graphics.Paint;?

import android.graphics.RectF;?

import android.view.View;?

?

public class MyView extends View {?

?

??? private int counter;?

??? private boolean isNewThread;?

??? private RectF rectf;?

??? private Paint p;?

??? private Timer timer;?

?

??? public MyView(Context context) {?

??????? super(context);?

??????? // TODO Auto-generated constructor stub?

??????? isNewThread = true;?

??????? rectf = new RectF(100, 50, 400, 350);?

??????? p = new Paint();?

??????? timer = new Timer();?

??? }?

?

??? public void newThread() {?

?

??????? timer.schedule(new TimerTask() {?

?

??????????? @Override?

??????????? public void run() {?

??????????????? // TODO Auto-generated method stub?

??????????????? postInvalidate();?

?????????????????

??????????? }?

??????? }, 0, 100);?

?

??? }?

?

??? @Override?

??? protected void onDraw(Canvas canvas) {?

??????? // TODO Auto-generated method stub?

??????? super.onDraw(canvas);?

??????? if (isNewThread) {?

??????????? newThread();?

??????????? isNewThread = false;?

??????? }?

??????? // 設定Canvas對象的背景顏色?

??????? canvas.drawColor(Color.YELLOW - counter);?

?

??????? // 設置畫筆顏色?

??????? p.setColor(Color.RED);?

??????? // 設置文字大小?

??????? p.setTextSize(40);?

??????? // 消除鋸齒?

??????? p.setFlags(Paint.ANTI_ALIAS_FLAG);?

?

??????? // 在canvas上繪制rect?

??????? canvas.drawArc(rectf, 0, counter, true, p);?

??????? if (counter == 400) {?

??????????? counter = 0;?

??????? }?

?

??????? canvas.drawText("counter = " + (counter++), 500, 200, p);?

?

??? }?

?

}?

http://blog.csdn.net/conowen/article/details/7843487

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