public class Toast { 
 
 public static final int LENGTH_SHORT = 0; 
 
 public static final int LENGTH_LONG = 1; 
 
 
 
 /** 
  * 構(gòu)造一個空的toast。你必須在調(diào)動show()之前，線調(diào)用setView() 
  * @param context 參數(shù)，application或者activity都可以 
  */ 
 public Toast(Context context) { 
  ... 
  //獲取系統(tǒng)內(nèi)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); 
 } 
 
 /** 
  * 在指定的時長顯示view視圖 
  */ 
 public void show() { 
  //如果mNextView為空，即沒有設置view 
  if (mNextView == null) { 
   throw new RuntimeException("setView must have been called"); 
  } 
 
  //通過系統(tǒng)服務，獲取通知管理器。看來這是使用系統(tǒng)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 
  } 
 } 
 
 
 /** 
  * 關(guān)閉一個正在顯示的toast, 或者取消一個未顯示的toast. 
  * 通常你不必調(diào)用它，在適當?shù)臅r長后它會自動消失的。 
  */ 
 public void cancel() { 
  mTN.hide(); 
 
  try { 
   getService().cancelToast(mContext.getPackageName(), mTN); 
  } catch (RemoteException e) { 
   // Empty 
  } 
 } 
 
 /** 
  * 設置toast顯示的視圖內(nèi)容，不單單是黑色的界面，你可以自己決定顯示什么 
  * @see #getView 
  */ 
 public void setView(View view) { 
  mNextView = view; 
 } 
 
 /** 
  * 設置時長，只能是下面這兩個常量值，沒什么卵用 
  * @see #LENGTH_SHORT 2000毫秒 
  * @see #LENGTH_LONG 3500毫秒 
  */ 
 public void setDuration(@Duration int duration) { 
  mDuration = duration; 
 } 
 
 
 /** 
  * 設置view的外間距，不用多說. 
  * 
  * @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; 
 } 
 
 
 /** 
  * 設置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; 
 } 
 
 
 
 /** 
  * 構(gòu)造一個只包含一個TextView的標準toast對象 
  * 
  * @param context 通常是application或者activity對象 
  * @param text  用于顯示的文本，可以是formatted text. 
  * @param duration 顯示時長. 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); 
 
  //包含了一個默認的TextView，這個textview的布局位置在 
 
com.android.internal.R.layout.transient_notification，可以去查看下內(nèi)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; 
 } 
 
 
 
 /** 
  * 更新通過makeText()方法創(chuàng)建出來的toast對象顯示的文本內(nèi)容 
  * @param s 待顯示的新文本內(nèi)容. 
  */ 
 public void setText(CharSequence s) { 
  if (mNextView == null) { 
   throw new RuntimeException("This Toast was not created with Toast.makeText()"); 
  } 
 
  /** 
   * 看來com.android.internal.R.layout.transient_notification布局里面的唯一的 
   * TextView標簽的id是R.id.message。拿到這個textview，設置新文本內(nèi)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; 
  } 
  //獲取遠程的通知服務 
  sService = INotificationManager.Stub.asInterface(ServiceManager.getService("notification")); 
  return sService; 
 } 
 
 
 //TN是一個瞬態(tài)通知的子類，里面包含顯示和隱藏兩個任務對象 
 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; 
   } 
  }; 
  
  //出現(xiàn)Handler了哦 
  final Handler mHandler = new Handler(); 
 
 
  /** 
   * 調(diào)度handleShow任務到執(zhí)行線程中 
   */ 
  @Override 
  public void show() { 
   if (localLOGV) Log.v(TAG, "SHOW: " + this); 
   //handler發(fā)送異步任務了 
   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(); 
 } 
}