Android Toast cancel和show 不踩中不会知道的坑

Toast.makeText(context, "要显示的提示", Toast.LENGTH_LONG).show();

 private Toast mShowingToast;
 private void showTestToast() {
     // mActivity是一个Activity对象，弹Toast一般用Activity类型的Context
     if (mShowingToast == null) {
         mShowingToast = Toast.makeText(mActivity, "要显示的提示", Toast.LENGTH_LONG);
     }
     mShowingToast.show();
 }

private Toast mShowingToast;
private void showTestToast() {
    // mActivity是一个Activity对象，弹Toast一般用Activity类型的Context
    if (mShowingToast == null) {
        mShowingToast = Toast.makeText(mActivity, "要显示的提示", Toast.LENGTH_LONG);
    }
    mShowingToast.cancel();
    mShowingToast.show();   // 会发现cancel之后调用show是show不出来的
}    

private Toast mShowingToast;
// 主线程的Handler对象
private Handler mHandler = new Handler(Looper.getMainLooper());
private void showTestToast() {
    // mActivity是一个Activity对象，弹Toast一般用Activity类型的Context
    if (mShowingToast == null) {
        mShowingToast = Toast.makeText(mActivity, "要显示的提示", Toast.LENGTH_LONG);
    }
    mShowingToast.cancel();
    mHandler.postDelayed(new Runnable() {
        @Override
        public void run() {
            mShowingToast.show();   // 会发现延迟之后就显示出来了
        }
    }, 200);  // 这个时间是自己拍脑袋写的，不影响体验就好，试过使用post也不行
}

/**
* Show the view for the specified duration.
*/
public void show() {
    if (mNextView == null) {
        throw new RuntimeException("setView must have been called");
    }

    INotificationManager service = getService();
    String pkg = mContext.getOpPackageName();
    TN tn = mTN;
    tn.mNextView = mNextView;

    try {
        service.enqueueToast(pkg, tn, mDuration);
    } catch (RemoteException e) {
        // Empty
    }
}

/**
 * Close the view if it's showing, or don't show it if it isn't showing yet.
 * You do not normally have to call this.  Normally view will disappear on its own
 * after the appropriate duration.
 */
public void cancel() {
    mTN.hide();

    try {
        getService().cancelToast(mContext.getPackageName(), mTN);
    } catch (RemoteException e) {
        // Empty
    }
}

这是Toast内部内TN的一个方法

/**
 * schedule handleHide into the right thread
 */
@Override
public void hide() {
    if (localLOGV) Log.v(TAG, "HIDE: " + this);
    mHandler.post(mHide);
}