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SVProgressHUD

代码片段

在SVProgressHUD.h中有如下代码：

#if __IPHONE_OS_VERSION_MAX_ALLOWED < 70000#define UI_APPEARANCE_SELECTOR#endif

__IPHONE_OS_VERSION_MAX_ALLOWED用法与意义请参考

UI_APPEARANCE_SELECTOR请参考

在申明方法是见到如下的用法：

+ (void)showWithMaskType:(SVProgressHUDMaskType)maskType __attribute__((deprecated("Use show and setDefaultMaskType: instead.")));

__attribute__ 可以设置函数属性（Function Attribute ）、变量属性（Variable Attribute ）和类型属性（Type Attribute ），详细的请见：

iOS UIWindow的理解

如下代码：

NSEnumerator *frontToBackWindows = [UIApplication.sharedApplication.windows reverseObjectEnumerator];    for (UIWindow *window in frontToBackWindows) {        BOOL windowOnMainScreen = window.screen == UIScreen.mainScreen;        BOOL windowIsVisible = !window.hidden && window.alpha > 0;        BOOL windowLevelNormal = window.windowLevel == UIWindowLevelNormal;        if(windowOnMainScreen && windowIsVisible && windowLevelNormal) {            [window addSubview:self.overlayView];            break;        }    }

UIWindow在显示的时候会根据UIWindowLevel进行排序的，即Level高的将排在所有Level比他低的层级的前面。下面我们来看UIWindowLevel的定义：

const UIWindowLevel UIWindowLevelNormal;const UIWindowLevel UIWindowLevelAlert;const UIWindowLevel UIWindowLevelStatusBar;typedef CGFloat UIWindowLevel;

它们级别的高低顺序从小到大为Normal < StatusBar < Alert

关于UIWindow的内容请参考：

willMoveToSuperview

在SVIndefiniteAnimatedView.m中如下：

- (void)willMoveToSuperview:(UIView*)newSuperview {    if (newSuperview) {        [self layoutAnimatedLayer];    } else {        [_indefiniteAnimatedLayer removeFromSuperlayer];        _indefiniteAnimatedLayer = nil;    }}

willMoveToSuperview的作用如下：

When a view is added to a superview, the system sends willMoveToSuperview: to the view. The parameter is the new superview.

When a view is removed from a superview, the system sends willMoveToSuperview: to the view. The parameter is nil.

You can’t prevent the system from sending willMoveToSuperview: when you remove the view from its superview, but you can check the parameter:

- (void)willMoveToSuperview:(UIView *)newSuperview {if (newSuperview != nil) {  // not a removeFromSuperview situation  }}

从bundle中加载图片

SVProgressHUD使用到的图片，位于SVProgressHUD.bundle中，其加载图片的方式如下：

//资源    NSBundle *bundle = [NSBundle bundleForClass:[SVProgressHUD class]];    NSURL *url = [bundle URLForResource:@"SVProgressHUD" withExtension:@"bundle"];    NSBundle *imageBundle = [NSBundle bundleWithURL:url];    //图片    UIImage* infoImage = [UIImage imageWithContentsOfFile:[imageBundle pathForResource:@"info" ofType:@"png"]];    UIImage* successImage = [UIImage imageWithContentsOfFile:[imageBundle pathForResource:@"success" ofType:@"png"]];    UIImage* errorImage = [UIImage imageWithContentsOfFile:[imageBundle pathForResource:@"error" ofType:@"png"]];

动画

fadeIn

渐入动画，开始出现时，alpha和HUD的transform为：

// Zoom HUD a little to make a nice appear / pop up animation    self.hudView.transform = CGAffineTransformScale(self.hudView.transform, 1.3, 1.3);    // Set initial values to handle iOS 7 (and above) UIToolbar which not answers well to hierarchy opacity change    self.alpha = 0.0f;    self.hudView.alpha = 0.0f;

动画结束的状态为：

__block void (^animationsBlock)(void) = ^{        __strong SVProgressHUD *strongSelf = weakSelf;        if(strongSelf) {            // Shrink HUD to finish pop up animation            strongSelf.hudView.transform = CGAffineTransformScale(strongSelf.hudView.transform, 1/1.3f, 1/1.3f);            strongSelf.alpha = 1.0f;            strongSelf.hudView.alpha = 1.0f;        }    };

相当于有一个弹性的动作。

动画完成后还有执行一段动作，定义为一个completionBlock：

__block void (^completionBlock)(void) = ^{        __strong SVProgressHUD *strongSelf = weakSelf;        if(strongSelf) {            /// Register observer <=> we now have to handle orientation changes etc.            [strongSelf registerNotifications];            // Post notification to inform user            [[NSNotificationCenter defaultCenter] postNotificationName:SVProgressHUDDidAppearNotification                                                                object:strongSelf                                                              userInfo:[strongSelf notificationUserInfo]];        }        // Update accesibilty        UIAccessibilityPostNotification(UIAccessibilityScreenChangedNotification, nil);        UIAccessibilityPostNotification(UIAccessibilityAnnouncementNotification, status);    };

动画执行的过程为：

//渐入动画，变化alpha和transfrom    if (self.fadeInAnimationDuration > 0) {        // Animate appearance        [UIView animateWithDuration:self.fadeInAnimationDuration                              delay:0                            options:(UIViewAnimationOptions) (UIViewAnimationOptionAllowUserInteraction | UIViewAnimationCurveEaseOut | UIViewAnimationOptionBeginFromCurrentState)                         animations:^{                             animationsBlock();                         } completion:^(BOOL finished) {                             completionBlock();                         }];    } else {        animationsBlock();        completionBlock();    }

fadeOut

fadeOut动画与fadeIn动画类似。

HUD实现

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