关于自定义 Alert

一、 window add subview

自定义 alert 的时候，没有做统一规划，都是实现一个 view，然后添加到 window 上。例如：

UIView *alert = [[UIView alloc] initWithFrame:];
[window addSubView:alert];
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这样本来也没有什么问题，有一天需求来了要支持 Voice Over，问题来了，直接盖上去的 view 不会自动聚焦，也就是手指左右滑动的时候，不能选中这个 view。而且不能 alert 出来的时候，不能自动读出。

二、利用Window 的 makeKeyAndVisible

然后想起以前 UIAlertView 显示的时候是有一个单独 window 的，于是也仿照这样，自己建一个 window，来显示 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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这样显示也正常，Voice Over 也能自动聚焦，但是手指头不小心点到空白区域的时候，还是会聚焦到下面的 view，不能只在 alert 上。而且还有一个严重的问题就是自定义密码输入空间，键盘有时候不会自动弹起来，这个以前是没问题的，不知道跟这个会不会有关系。

三、presentViewController

仿照 UIAlertController 的方式，利用 presentViewController来显示提示框，这个没有上面的问题，Voice over也能自定聚焦，也不会点到下面的 view。效果还可以。

    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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使用 presentViewController 的时候，由哪个ViewController来 present 也是个问题，统一处理的话，用跟 UITabBarController 或者是 UINavigationController都是不错的方案，例如：

UIViewController * root = [UIApplication sharedApplication].delegate.window.rootViewController;
        if ([root isKindOfClass:[UITabBarController class]]) {
            UITabBarController *tab = (UITabBarController *)root;
            if (tab.tabBar.hidden) {
                //
                UIViewController *selectedVC = tab.selectedViewController;
                self.mShowInViewController = selectedVC;
            } else {
                self.mShowInViewController = root;
            }
        } else {
            self.mShowInViewController = root;
        }

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但是这里有问题，就是容易和其他的弹窗冲突，造成alert弹不出来，而且如果 alert 不释放的话，连弹多次还容易 crash

Application tried to present modally an active controller

所以呢可以把 Window 和 present结合起来使用。

alertWindow 一定要在 alert 消失的时候给释放掉

// method2: 问题是如果self 消失的时候不释放，那么 window 会一直存在接收事件，造成 rootWindow 无法接收事件
        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;
        }
        
        // 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.mShowInViewController = self.alertWindow.rootViewController;


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四、完整代码

完整代码在这里

一、 window add subview

二、利用Window 的 makeKeyAndVisible

三、presentViewController

四、完整代码

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