Toast 和 Looper，一个属于 android.widget，一个属于 android.os，两个貌似联系不怎么紧密的类，却通过下面这个异常联系到了一起：

E/AndroidRuntime( 1819): java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
E/AndroidRuntime( 1819):        at android.os.Handler.<init>(Handler.java:121)
E/AndroidRuntime( 1819):        at android.widget.Toast.<init>(Toast.java:397)
E/AndroidRuntime( 1819):        at android.widget.Toast.makeText(Toast.java:230)
E/AndroidRuntime( 1819):        at android.widget.Toast.makeText(Toast.java:256)

由以上的错误信息可以看出：程序要创建 handler，但是发现 Looper.prepare 还没有被调用。通过 Android SDK 中的 Reference 可以看到，Looper、Handler 的调用是非常有讲究的，如下面示例代码：

class LooperThread extends Thread {
    public Handler mHandler;
 
    public void run() {
        Looper.prepare();
 
        mHandler = new Handler() {
            public void handleMessage(Message msg) {
                // process incoming messages here
            }
        };
 
        Looper.loop();
    }
}

言归正题，继续寻找 Toast、Looper 和 Handler 三者之间的联系，也许谜底就能解开了。欲揭谜底，从源码入手是一条捷径。

Toast.java 的第230行的代码是创建一个新的 Toast 实例，而实例化的过程中，就需要执行第397行，也就是声明并创建 Handler 的实例。那么来看 Handler.java 的第121行到底做了什么，如下所示：

mLooper = Looper.myLooper();
if (mLooper == null) {
    throw new RuntimeException(
        "Can't create handler inside thread that has not called Looper.prepare()");
}

到此，距离真相的解开近了一大步，既然抛出了 RuntimeException，那么 mLooper 肯定是 null，但是为什么 Looper.myLooper() 会返回 null？继续进入到 Looper.java 中寻根究底。

/**
 * Return the Looper object associated with the current thread.  Returns
 * null if the calling thread is not associated with a Looper.
 */
public static final Looper myLooper() {
    return (Looper)sThreadLocal.get();
}

以上就是 myLooper() 方法的真实面貌，通过注释可以看出问题的真正原因在于当前线程并没有绑定 Looper，返回为 null 是正确但非正常的结果。

问题的根本原因已经解开，但是另外一个疑团也就产生了：为何当前线程没有 Looper 呢？经过对代码进行 review，原因找到了：当事者在 non-UI 线程进行 Toast.makeText

package com.touch;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Toast;

public class TouchActivity extends Activity {
           
  
           
          /** Called when the activity is first created. */ 
          @Override 
          public void onCreate(Bundle savedInstanceState) { 
              super.onCreate(savedInstanceState); 
              //setContentView(R.layout.main); 
              MyView view = new MyView(this); 
              setContentView(view); 
              view.requestFocus(); 
               
          } 
      } 
       
      class MyView extends View{ 
          private Paint mPaint, pointPaint;
          private Bitmap mBitmap; 
           Context mContext;
           int n;
          public MyView(Context context) { 
              super(context); 
              mContext = context;
              mPaint = new Paint(); 
              mPaint.setAntiAlias(true); 
              mPaint.setARGB(0, 0xff, 0, 0);
              pointPaint = new Paint();
              pointPaint.setARGB(150, 0, 255, 255);
              pointPaint.setTextSize(30);
              DisplayMetrics dm = new DisplayMetrics();
              dm=getResources().getDisplayMetrics();
              mBitmap = Bitmap.createBitmap(dm.widthPixels, dm.heightPixels, Bitmap.Config.RGB_565); 
       
          } 
           
          @Override 
          protected void onDraw(Canvas canvas) { 
              super.onDraw(canvas); 
               
              if(mBitmap != null) 
                  canvas.drawBitmap(mBitmap, 0, 0, null); 
       
          } 
          @Override 
          public boolean onTouchEvent(MotionEvent event) { 
              int N = event.getHistorySize(); 
              float x = 0; 
              float y = 0; 
              x = event.getX(); 
              y = event.getY(); 
              Canvas canvas = new Canvas(); 
              canvas.setBitmap(mBitmap); 
              if(event.getAction() == MotionEvent.ACTION_DOWN){
                  mPaint.setARGB(0xff, 0, 0, 0);
                  canvas.drawPaint(mPaint);
                  n=0;
                  invalidate();
              }else{
                  ++n;
                  mPaint.setARGB(100, 0xff, 0, 0); 
                  canvas.drawCircle(x, y, 4, mPaint); 
                  invalidate(); 
              }
             
              if(event.getAction() == MotionEvent.ACTION_UP){
                  canvas.drawText("点个数="+n, mBitmap.getWidth()/2-30, 30, pointPaint);
                  invalidate();
              }
             
              return true; 
          } 
           
}

Entity:
An Entitiy is an object that can be drawn, like Sprites, Rectangles, Text or Lines. An Entity has a position/rotation/scale/color/etc...

一个entitiy是一个可以被画的物体，像Sprites，矩形，文本或线。一个实体有一个位置/旋转/重力/彩色/等等

1.IEntity接口

public interface IEntity extends IDrawable, IUpdateHandler {

	public int getZIndex();
	public void setZIndex(final int pZIndex);
}

2.IDrawable接口

public interface IDrawable {

	public void onDraw(final GL10 pGL, final Camera pCamera);
}

3.IUpdateHandler接口

public interface IUpdateHandler {

	public void onUpdate(final float pSecondsElapsed);
	public void reset();
}