public class Toast { 
 
 public static final int LENGTH_SHORT = 0; 
 
 public static final int LENGTH_LONG = 1; 
 
 
 
 /** 
  * 构造一个空的toast。你必须在调动show()之前，线调用setView() 
  * @param context 参数，application或者activity都可以 
  */ 
 public Toast(Context context) { 
  ... 
  //获取系统内置的toast_y_offset常量值 
  mTN.mY = context.getResources().getDimensionPixelSize( 
    com.android.internal.R.dimen.toast_y_offset); 
  mTN.mGravity = context.getResources().getInteger( 
    com.android.internal.R.integer.config_toastDefaultGravity); 
 } 
 
 /** 
  * 在指定的时长显示view视图 
  */ 
 public void show() { 
  //如果mNextView为空，即没有设置view 
  if (mNextView == null) { 
   throw new RuntimeException("setView must have been called"); 
  } 
 
  //通过系统服务，获取通知管理器。看来这是使用系统通知？ 
  INotificationManager service = getService(); 
  String pkg = mContext.getOpPackageName(); 
  TN tn = mTN; 
  tn.mNextView = mNextView; 
 
  try { 
   service.enqueueToast(pkg, tn, mDuration); 
  } catch (RemoteException e) { 
   // Empty 
  } 
 } 
 
 
 /** 
  * 关闭一个正在显示的toast, 或者取消一个未显示的toast. 
  * 通常你不必调用它，在适当的时长后它会自动消失的。 
  */ 
 public void cancel() { 
  mTN.hide(); 
 
  try { 
   getService().cancelToast(mContext.getPackageName(), mTN); 
  } catch (RemoteException e) { 
   // Empty 
  } 
 } 
 
 /** 
  * 设置toast显示的视图内容，不单单是黑色的界面，你可以自己决定显示什么 
  * @see #getView 
  */ 
 public void setView(View view) { 
  mNextView = view; 
 } 
 
 /** 
  * 设置时长，只能是下面这两个常量值，没什么卵用 
  * @see #LENGTH_SHORT 2000毫秒 
  * @see #LENGTH_LONG 3500毫秒 
  */ 
 public void setDuration(@Duration int duration) { 
  mDuration = duration; 
 } 
 
 
 /** 
  * 设置view的外间距，不用多说. 
  * 
  * @param horizontalMargin The horizontal margin, in percentage of the 
  *  container width, between the container's edges and the 
  *  notification 
  * @param verticalMargin The vertical margin, in percentage of the 
  *  container height, between the container's edges and the 
  *  notification 
  */ 
 public void setMargin(float horizontalMargin, float verticalMargin) { 
  mTN.mHorizontalMargin = horizontalMargin; 
  mTN.mVerticalMargin = verticalMargin; 
 } 
 
 
 /** 
  * 设置notification在屏幕中的方位，大家都知道.上中下左中右什么的都有 
  * @see android.view.Gravity 
  * @see #getGravity 
  */ 
 public void setGravity(int gravity, int xOffset, int yOffset) { 
  mTN.mGravity = gravity; 
  mTN.mX = xOffset; 
  mTN.mY = yOffset; 
 } 
 
 
 
 /** 
  * 构造一个只包含一个TextView的标准toast对象 
  * 
  * @param context 通常是application或者activity对象 
  * @param text  用于显示的文本，可以是formatted text. 
  * @param duration 显示时长. LENGTH_SHORT或LENGTH_LONG 
  * 
  */ 
 public static Toast makeText(Context context, CharSequence text, @Duration int duration) { 
  Toast result = new Toast(context); 
 
  LayoutInflater inflate = (LayoutInflater) 
    context.getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
 
  //包含了一个默认的TextView，这个textview的布局位置在 
 
com.android.internal.R.layout.transient_notification，可以去查看下内容 
  View v = inflate.inflate(com.android.internal.R.layout.transient_notification, null); 
  TextView tv = (TextView)v.findViewById(com.android.internal.R.id.message); 
  tv.setText(text); 
   
  result.mNextView = v; 
  result.mDuration = duration; 
 
  return result; 
 } 
 
 
 
 /** 
  * 更新通过makeText()方法创建出来的toast对象显示的文本内容 
  * @param s 待显示的新文本内容. 
  */ 
 public void setText(CharSequence s) { 
  if (mNextView == null) { 
   throw new RuntimeException("This Toast was not created with Toast.makeText()"); 
  } 
 
  /** 
   * 看来com.android.internal.R.layout.transient_notification布局里面的唯一的 
   * TextView标签的id是R.id.message。拿到这个textview，设置新文本内容 
   */ 
  TextView tv = (TextView) mNextView.findViewById(com.android.internal.R.id.message); 
  if (tv == null) { 
   throw new RuntimeException("This Toast was not created with Toast.makeText()"); 
  } 
  tv.setText(s); 
 } 
 
 
 static private INotificationManager getService() { 
  if (sService != null) { 
   return sService; 
  } 
  //获取远程的通知服务 
  sService = INotificationManager.Stub.asInterface(ServiceManager.getService("notification")); 
  return sService; 
 } 
 
 
 //TN是一个瞬态通知的子类，里面包含显示和隐藏两个任务对象 
 private static class TN extends ITransientNotification.Stub { 
  final Runnable mShow = new Runnable() { 
   @Override 
   public void run() { 
    handleShow(); 
   } 
  }; 
 
  final Runnable mHide = new Runnable() { 
   @Override 
   public void run() { 
    handleHide(); 
    // Don't do this in handleHide() because it is also invoked by handleShow() 
    mNextView = null; 
   } 
  }; 
  
  //出现Handler了哦 
  final Handler mHandler = new Handler(); 
 
 
  /** 
   * 调度handleShow任务到执行线程中 
   */ 
  @Override 
  public void show() { 
   if (localLOGV) Log.v(TAG, "SHOW: " + this); 
   //handler发送异步任务了 
   mHandler.post(mShow); 
  } 
 
 
  /** 
   * 同上 
   */ 
  @Override 
  public void hide() { 
   if (localLOGV) Log.v(TAG, "HIDE: " + this); 
   mHandler.post(mHide); 
  } 
 
  //... 
 } 
 
} 

Toast.makeText(context, text, duration).show(); 

Toast toast = Toast.makeText(context, text, duration); 
pre name="code" class="html"> toast.setView(view); 
toast.setText(s); 
toast.setGravity(gravity, xOffset, yOffset); 
toast.setDuration(duration); 
toast.show();

Toast toast = new Toast(); 
toast.setView(view); 
toast.setText(s); 
toast.setGravity(gravity, xOffset, yOffset); 
toast.setDuration(duration); 
toast.show(); 

public class T { 
 private static Toast toast; 
 
 public static void show(Context context, String msg) { 
  if (toast == null) { 
   toast = Toast.makeText(context, msg, Toast.LENGTH_SHORT); 
  } else { 
   toast.setText(msg); 
  } 
  toast.show(); 
 } 
}