一、 window add subview

自定義 alert 的時候，沒有做統一規劃，都是實現一個 view，然後新增到 window 上。例如：

UIView *alert = [[UIView alloc] initWithFrame:];
[window addSubView:alert];
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這樣本來也沒有什麼問題，有一天需求來了要支援 Voice Over，問題來了，直接蓋上去的 view 不會自動聚焦，也就是手指左右滑動的時候，不能選中這個 view。而且不能 alert 出來的時候，不能自動讀出。

二、利用Window 的 makeKeyAndVisible

然後想起以前 UIAlertView 顯示的時候是有一個單獨 window 的，於是也仿照 這樣，自己建一個 window，來顯示 alert，

    self.alertWindow = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
    self.alertWindow.rootViewController = [[UIViewController alloc] init];

    id<UIApplicationDelegate> delegate = [UIApplication sharedApplication].delegate;
    // Applications that does not load with UIMainStoryboardFile might not have a window property:
    if
 
 ([delegate respondsToSelector:@selector(window)]) {
        // we inherit the main window's tintColor
        self.alertWindow.tintColor = delegate.window.tintColor;
    }
    self.alertWindow.hidden = YES;
    self.frame = self.alertWindow.bounds;

    // window level is above the top window (this makes the alert, if it'
 
s a sheet, show over the keyboard)
    UIWindow *topWindow = [UIApplication sharedApplication].windows.lastObject;
    self.alertWindow.windowLevel = topWindow.windowLevel + 1;

    [self.alertWindow makeKeyAndVisible];
    [self.alertWindow addSubview:self];


    [UIView animateWithDuration:0.25 animations:^{
        self.alertWindow.hidden = NO;
    } completion:nil];

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這樣顯示也正常，Voice Over 也能自動聚焦，但是 手指頭不小心點到空白區域的時候，還是會聚焦到下面的 view，不能只在 alert 上。 而且還有一個嚴重的問題 就是 自定義密碼輸入空間，鍵盤有時候不會自動彈起來，這個以前是沒問題的，不知道跟這個會不會有關係。

三、presentViewController

仿照 UIAlertController 的方式，利用 presentViewController來顯示提示框，這個沒有上面的問題，Voice over也能自定聚焦，也不會點到下面的 view。效果還可以。

    self.mShowInViewController.definesPresentationContext = YES;
    self.mShowInViewController.providesPresentationContextTransitionStyle = YES;

    if (!self.mShowViewController) {
        UIViewController *vc = [[UIViewController alloc] init];
        vc.modalPresentationStyle = UIModalPresentationOverCurrentContext;
        UIView *backgroundView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, kScreenWidth, kScreenHeight)];
        backgroundView.backgroundColor = RGBA_COLOR_HEX(0x000000, 0.5);
        vc.backgroundView = backgroundView;
        if (self.alertType == CustomAlertTypeActionSheet) {
            UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(onClickBackground)];
            tap.delegate = self;
            [self addGestureRecognizer:tap];
        }
        
        [vc.view addSubview:backgroundView];
        vc.view.backgroundColor = [UIColor clearColor];
//        vc.backgroundView.alpha = 0;
        self.mShowViewController = vc;
    }
}

if (!self.superview) {
        [self.mShowViewController.view addSubview:self];
    }
    self.frame = CGRectMake(0, 0, kScreenWidth, kScreenHeight);
    
    WEAKSELF
    [self.mShowInViewController presentViewController:self.mShowViewController animated:NO completion:^{
        [UIView animateWithDuration:0.25 animations:^{
            weak_self.mShowViewController.view.alpha = 1;
        } completion:^(BOOL finished) {
            if (complete) {
                complete(YES);
            }
        }];
    }];
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