常見的Dialog，常用的isShowing方法，用此方法常判斷dialog是否正在顯示，但是有時發現dialog沒有顯示，此方法也是返回true，這就尷尬了。

取消顯示dialog的方法

一、點選返回按鈕或者點選dialog之外的螢幕

/**
     * Called when the dialog has detected the user's press of the back
     * key.  The default implementation simply cancels the dialog (only if
     * it is cancelable), but you can override this to do whatever you want.
     */
 

    public void onBackPressed() {
        if (mCancelable) {
            cancel();
        }
    }

點選返回按鈕，最後呼叫了cancel的方法；

/**
     * Called when a touch screen event was not handled by any of the views
     * under it. This is most useful to process touch events that happen outside
     * of your window bounds, where
 
 there is no view to receive it.
     * 
     * @param event The touch screen event being processed.
     * @return Return true if you have consumed the event, false if you haven't.
     *         The default implementation will cancel the dialog when a touch
     *         happens outside of the window bounds.
     */
    public boolean
 
 onTouchEvent(@NonNull MotionEvent event) {
        if (mCancelable && mShowing && mWindow.shouldCloseOnTouch(mContext, event)) {
            cancel();
            return true;
        }

        return false;
    }

點選螢幕之外最後也是呼叫cancel方法

二、看看cancel()方法

/**
     * Cancel the dialog.  This is essentially the same as calling {@link #dismiss()}, but it will
     * also call your {@link DialogInterface.OnCancelListener} (if registered).
     */
    @Override
    public void cancel() {
        if (!mCanceled && mCancelMessage != null) {
            mCanceled = true;
            // Obtain a new message so this dialog can be re-used
            Message.obtain(mCancelMessage).sendToTarget();
        }
        dismiss();
    }

看到原始碼，cancel方法最後還是呼叫了dismiss方法

三、看看dimiss()方法

/**
     * Dismiss this dialog, removing it from the screen. This method can be
     * invoked safely from any thread.  Note that you should not override this
     * method to do cleanup when the dialog is dismissed, instead implement
     * that in {@link #onStop}.
     */
    @Override
    public void dismiss() {
        if (Looper.myLooper() == mHandler.getLooper()) {
            dismissDialog();
        } else {
            mHandler.post(mDismissAction);
        }
    }

看到原始碼，dismiss()會呼叫dismissDialog()方法

四、看看dismissDialog()方法

void dismissDialog() {
        if (mDecor == null || !mShowing) {
            return;
        }

        if (mWindow.isDestroyed()) {
            Log.e(TAG, "Tried to dismissDialog() but the Dialog's window was already destroyed!");
            return;
        }

        try {
            mWindowManager.removeViewImmediate(mDecor);
        } finally {
            if (mActionMode != null) {
                mActionMode.finish();
            }
            mDecor = null;
            mWindow.closeAllPanels();
            onStop();
            mShowing = false;

            sendDismissMessage();
        }
    }

看到原始碼，最後將mShowing = false;

五、再看看hide()方法

/**
     * Hide the dialog, but do not dismiss it.
     */
    public void hide() {
        if (mDecor != null) {
            mDecor.setVisibility(View.GONE);
        }
    }

可以看到並沒有將mShowing賦值。所以呼叫hide方法，隱藏dialog但是isShowing方法還是會返回true。

總結：
1.點選返回按鍵或者點選dialog之外的螢幕->cancel()->dismiss()->dismissDialog->mShowing = false;
此時dialog沒有顯示， isShowing方法返回false；

2.呼叫hide()->dialog隱藏，mShowing依然是true；
此時dialog沒有顯示，isShowing方法返回true；