主要我之前用的時候不知道dismiss和cancel有啥區別。。。然後今天想起來了就去查了一下，順便記下來備忘。

dismiss:大概就是刪除檢視，呼叫Onstop回撥，並把mShowing置為false。

    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();
        }
    }
 

cancel：也呼叫了dismiss，只不過先判斷了mCancelMessage是否為空

    @Override
    public void cancel() {
        if (!mCanceled && mCancelMessage != null) {
            mCanceled = true;
            Message.obtain(mCancelMessage).sendToTarget();
        }
        dismiss();
    }

mCancelMessage實際上是把listener封裝成obj的Message

    public void setOnCancelListener(@Nullable OnCancelListener listener) {
        if (mCancelAndDismissTaken != null) {
            throw new IllegalStateException(
                    "OnCancelListener is already taken by "
                    + mCancelAndDismissTaken + " and can not be replaced.");
        }
        if (listener != null) {
            mCancelMessage = mListenersHandler.obtainMessage(CANCEL, listener);
        } else {
            mCancelMessage = null;
        }
    }
 

hide：這是幹嘛的。。。隱藏起來又不銷燬，有啥用？萬一後面忘了呢，銷燬Activity的時候就會報錯：android.view.WindowLeaked: Activity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorViewthat was originally added here，所以建議不用。

    public void hide() {
        if (mDecor != null) {
            mDecor.setVisibility(View.GONE);
        }
    }

 總結：

建議用dismiss，這個比cancel少一個判斷，一般來說是夠用了，當然如果你有CancelListener的話就用cancel。。。