众所周知 SVProgressHUD 是一个简洁易用的 HUD 库，我想探寻简洁易用背后的原理。
Singleton
SVProgressHUD 同 MBProgressHUD 一样，都是 UIView 的子类，不同与 MB , SV 提供的是单例，这也是它简洁的一大因素。
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+ (SVProgressHUD*)sharedView {
static dispatch_once_t once;
static SVProgressHUD *sharedView;
#if !defined(SV_APP_EXTENSIONS)
dispatch_once(&once, ^{ sharedView = [[self alloc] initWithFrame:[[[UIApplication sharedApplication] delegate] window].bounds]; });
#else
dispatch_once(&once, ^{ sharedView = [[self alloc] initWithFrame:[[UIScreen mainScreen] bounds]]; });
#endif
return sharedView;
}
常规的单例创建，根据是否是 App Extension 进行了判断以确定 Frame 大小
Show Methods
SV 不像 MB 可以有较高的自由度定制，所以为了简洁，暴露的全是类方法
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+ (void)show;
+ (void)showWithStatus:(nullable NSString*)status;
+ (void)showProgress:(float)progress;
+ (void)showProgress:(float)progress status:(nullable NSString*)status;
没有列举全部，因为都不是重点，他们不添加图片的最终会调用主方法:
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- (void)showProgress:(float)progress status:(NSString*)status { }
有图的调用:
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- (void)showImage:(UIImage*)image status:(NSString*)status duration:(NSTimeInterval)duration { }
以无图为例:
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- (void)showProgress:(float)progress status:(NSString*)status {
__weak SVProgressHUD *weakSelf = self;
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
__strong SVProgressHUD *strongSelf = weakSelf;
if(strongSelf){
if(strongSelf.fadeOutTimer) {
strongSelf.activityCount = 0;
}
// Set properties
strongSelf.fadeOutTimer = nil;
strongSelf.graceTimer = nil;
...
// Choose the "right" indicator depending on the progress
if(progress >= 0) {
...
// Add ring to HUD
if(!strongSelf.ringView.superview){
[strongSelf.hudView.contentView addSubview:strongSelf.ringView];
}
if(!strongSelf.backgroundRingView.superview){
[strongSelf.hudView.contentView addSubview:strongSelf.backgroundRingView];
}
...
} else {
...
// Add indefiniteAnimatedView to HUD
[strongSelf.hudView.contentView addSubview:strongSelf.indefiniteAnimatedView];
if([strongSelf.indefiniteAnimatedView respondsToSelector:@selector(startAnimating)]) {
[(id)strongSelf.indefiniteAnimatedView startAnimating];
}
...
}
// Fade in delayed if a grace time is set
if (self.graceTimeInterval > 0.0 && self.backgroundView.alpha == 0.0f) {
strongSelf.graceTimer = [NSTimer timerWithTimeInterval:self.graceTimeInterval target:strongSelf selector:@selector(fadeIn:) userInfo:nil repeats:NO];
[[NSRunLoop mainRunLoop] addTimer:strongSelf.graceTimer forMode:NSRunLoopCommonModes];
} else {
[strongSelf fadeIn:nil];
}
...
}
}];
}
首先是 weakSelf strongSelf 标准写法，老生常谈了避免循环引用以及提前释放。
然后设置一些属性，根据 progress 判断选择合适的指示符。
然后根据是否设置了 gracetime 调用或者延时调用 fadeIn 方法。
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- (void)fadeIn:(id)data {
// Update the HUDs frame to the new content and position HUD
[self updateHUDFrame];
[self positionHUD:nil];
...
// Show if not already visible
if(self.backgroundView.alpha != 1.0f) {
...
__block void (^animationsBlock)(void) = ^{
// Zoom HUD a little to make a nice appear / pop up animation
self.hudView.transform = CGAffineTransformIdentity;
// Fade in all effects (colors, blur, etc.)
[self fadeInEffects];
};
__block void (^completionBlock)(void) = ^{
// Check if we really achieved to show the HUD (<=> alpha)
// and the change of these values has not been cancelled in between e.g. due to a dismissal
if(self.backgroundView.alpha == 1.0f){
// Register observer <=> we now have to handle orientation changes etc.
[self registerNotifications];
...
// Dismiss automatically if a duration was passed as userInfo. We start a timer
// which then will call dismiss after the predefined duration
if(duration){
self.fadeOutTimer = [NSTimer timerWithTimeInterval:[(NSNumber *)duration doubleValue] target:self selector:@selector(dismiss) userInfo:nil repeats:NO];
[[NSRunLoop mainRunLoop] addTimer:self.fadeOutTimer forMode:NSRunLoopCommonModes];
}
}
};
// Animate appearance
if (self.fadeInAnimationDuration > 0) {
// Animate appearance
[UIView animateWithDuration:self.fadeInAnimationDuration
delay:0
options:(UIViewAnimationOptions) (UIViewAnimationOptionAllowUserInteraction | UIViewAnimationCurveEaseIn | UIViewAnimationOptionBeginFromCurrentState)
animations:^{
animationsBlock();
} completion:^(BOOL finished) {
completionBlock();
}];
} else {
animationsBlock();
completionBlock();
}
// Inform iOS to redraw the view hierarchy
[self setNeedsDisplay];
} else {
// Update accessibility
UIAccessibilityPostNotification(UIAccessibilityScreenChangedNotification, nil);
UIAccessibilityPostNotification(UIAccessibilityAnnouncementNotification, self.statusLabel.text);
// Dismiss automatically if a duration was passed as userInfo. We start a timer
// which then will call dismiss after the predefined duration
if(duration){
self.fadeOutTimer = [NSTimer timerWithTimeInterval:[(NSNumber *)duration doubleValue] target:self selector:@selector(dismiss) userInfo:nil repeats:NO];
[[NSRunLoop mainRunLoop] addTimer:self.fadeOutTimer forMode:NSRunLoopCommonModes];
}
}
}
其实就是如果已经显示完全了就 dismiss，如果没有显示完全就先显示完全再 dismiss
Dismiss Methods
同样 dismiss 暴露的也全部是类方法
+ (void)popActivity;+ (void)dismiss;+ (void)dismissWithCompletion:(nullable SVProgressHUDDismissCompletion)completion;+ (void)dismissWithDelay:(NSTimeInterval)delay;+ (void)dismissWithDelay:(NSTimeInterval)delay completion:(nullable SVProgressHUDDismissCompletion)completion;
同样也是最终调用主方法： - (void)dismissWithDelay:(NSTimeInterval)delay completion:(SVProgressHUDDismissCompletion)completion 这个方法其实逻辑跟 show 也差不多就是最终把 controlView backgroundView budView 都 remove 掉然后再把自己 remove，还有取消动画 progress 归零等
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- (void)dismissWithDelay:(NSTimeInterval)delay completion:(SVProgressHUDDismissCompletion)completion {
__weak SVProgressHUD *weakSelf = self;
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
__strong SVProgressHUD *strongSelf = weakSelf;
if(strongSelf){
...
__block void (^completionBlock)(void) = ^{
// Check if we really achieved to dismiss the HUD (<=> alpha values are applied)
// and the change of these values has not been cancelled in between e.g. due to a new show
if(self.backgroundView.alpha == 0.0f){
// Clean up view hierarchy (overlays)
[strongSelf.controlView removeFromSuperview];
[strongSelf.backgroundView removeFromSuperview];
[strongSelf.hudView removeFromSuperview];
[strongSelf removeFromSuperview];
// Reset progress and cancel any running animation
strongSelf.progress = SVProgressHUDUndefinedProgress;
[strongSelf cancelRingLayerAnimation];
[strongSelf cancelIndefiniteAnimatedViewAnimation];
...
// Run an (optional) completionHandler
if (completion) {
completion();
}
}
};
// UIViewAnimationOptionBeginFromCurrentState AND a delay doesn't always work as expected
// When UIViewAnimationOptionBeginFromCurrentState is set, animateWithDuration: evaluates the current
// values to check if an animation is necessary. The evaluation happens at function call time and not
// after the delay => the animation is sometimes skipped. Therefore we delay using dispatch_after.
dispatch_time_t dipatchTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delay * NSEC_PER_SEC));
dispatch_after(dipatchTime, dispatch_get_main_queue(), ^{
if (strongSelf.fadeOutAnimationDuration > 0) {
// Animate appearance
[UIView animateWithDuration:strongSelf.fadeOutAnimationDuration
delay:0
options:(UIViewAnimationOptions) (UIViewAnimationOptionAllowUserInteraction | UIViewAnimationCurveEaseOut | UIViewAnimationOptionBeginFromCurrentState)
animations:^{
animationsBlock();
} completion:^(BOOL finished) {
completionBlock();
}];
} else {
animationsBlock();
completionBlock();
}
});
// Inform iOS to redraw the view hierarchy
[strongSelf setNeedsDisplay];
}
}];
}
这里有一个小细节，注释也写的很清楚了。就是UIViewAnimationOptionBeginFromCurrentState 搭配 delay 总是有点跳动画的毛病，所以SV这里用 dispatch_after 来延时。
总结
总体来讲，SVProgressHUD 还是简洁易用为主，Github上给出的使用建议都是这种：
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[SVProgressHUD show];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// time-consuming task
dispatch_async(dispatch_get_main_queue(), ^{
[SVProgressHUD dismiss];
});
});
源码实现确实也不算复杂，个人还是比较喜欢用。