对MBProgressHUD第三方进行源码分析

GitHub源码地址，及时更新：iOS-Source-Code-Analyze

MBProgressHUD是一个为iOS app添加透明浮层 HUD 的第三方框架。作为一个 UI 层面的框架，它的实现很简单，但是其中也有一些非常有意思的代码。

MBProgressHUD

MBProgressHUD是一个 UIView 的子类，它提供了一系列的创建 HUD 的方法。我们在这里会主要介绍三种使用 HUD 的方法。

+ showHUDAddedTo:animated:

- showAnimated:whileExecutingBlock:onQueue:completionBlock:

- showWhileExecuting:onTarget:withObject:

+ showHUDAddedTo:animated:

MBProgressHUD 提供了一对类方法 + showHUDAddedTo:animated: 和 + hideHUDForView:animated: 来创建和隐藏 HUD, 这是创建和隐藏 HUD 最简单的一组方法

+ (MB_INSTANCETYPE)showHUDAddedTo:(UIView *)view animated:(BOOL)animated {
MBProgressHUD *hud = [[self alloc] initWithView:view];
hud.removeFromSuperViewOnHide = YES;
[view addSubview:hud];
[hud show:animated];
return MB_AUTORELEASE(hud);
}

- initWithView:

首先调用 + alloc - initWithView: 方法返回一个 MBProgressHUD 的实例, - initWithView: 方法会调用当前类的 - initWithFrame: 方法。

通过 - initWithFrame: 方法的执行，会为 MBProgressHUD 的一些属性设置一系列的默认值。

- (id)initWithFrame:(CGRect)frame {
self = [super initWithFrame:frame];
if (self) {
// Set default values for properties
self.animationType = MBProgressHUDAnimationFade;
self.mode = MBProgressHUDModeIndeterminate;
...
// Make it invisible for now
self.alpha = 0.0f;
[self registerForKVO];
...
}
return self;
}

在 MBProgressHUD 初始化的过程中, 有一个需要注意的方法 - registerForKVO, 我们会在之后查看该方法的实现。

- show:

在初始化一个 HUD 并添加到 view 上之后, 这时 HUD 并没有显示出来, 因为在初始化时, view.alpha 被设置为 0。所以我们接下来会调用 - show: 方法使 HUD 显示到屏幕上。

- (void)show:(BOOL)animated {
NSAssert([NSThread isMainThread], @"MBProgressHUD needs to be accessed on the main thread.");
useAnimation = animated;
// If the grace time is set postpone the HUD display
if (self.graceTime > 0.0) {
NSTimer *newGraceTimer = [NSTimer timerWithTimeInterval:self.graceTime target:self selector:@selector(handleGraceTimer:) userInfo:nil repeats:NO];
[[NSRunLoop currentRunLoop] addTimer:newGraceTimer forMode:NSRunLoopCommonModes];
self.graceTimer = newGraceTimer;
}
// ... otherwise show the HUD imediately
else {
[self showUsingAnimation:useAnimation];
}
}

因为在 iOS 开发中，对于 UIView 的处理必须在主线程中, 所以在这里我们要先用 [NSThread isMainThread] 来确认当前前程为主线程。

如果 graceTime 为 0，那么直接调用 - showUsingAnimation: 方法, 否则会创建一个 newGraceTimer 当然这个 timer 对应的 selector 最终调用的也是 - showUsingAnimation: 方法。

- showUsingAnimation:

- (void)showUsingAnimation:(BOOL)animated {
// Cancel any scheduled hideDelayed: calls
[NSObject cancelPreviousPerformRequestsWithTarget:self];
[self setNeedsDisplay];
if (animated && animationType == MBProgressHUDAnimationZoomIn) {
self.transform = CGAffineTransformConcat(rotationTransform, CGAffineTransformMakeScale(0.5f, 0.5f));
} else if (animated && animationType == MBProgressHUDAnimationZoomOut) {
self.transform = CGAffineTransformConcat(rotationTransform, CGAffineTransformMakeScale(1.5f, 1.5f));
}
self.showStarted = [NSDate date];
// Fade in
if (animated) {
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationDuration:0.30];
self.alpha = 1.0f;
if (animationType == MBProgressHUDAnimationZoomIn || animationType == MBProgressHUDAnimationZoomOut) {
self.transform = rotationTransform;
}
[UIView commitAnimations];
}
else {
self.alpha = 1.0f;
}
}

这个方法的核心功能就是根据 animationType 为 HUD 的出现添加合适的动画。

typedef NS_ENUM(NSInteger, MBProgressHUDAnimation) {
/** Opacity animation */
MBProgressHUDAnimationFade,
/** Opacity + scale animation */
MBProgressHUDAnimationZoom,
MBProgressHUDAnimationZoomOut = MBProgressHUDAnimationZoom,
MBProgressHUDAnimationZoomIn
};

它在方法刚调用时会通过 - cancelPreviousPerformRequestsWithTarget: 移除附加在 HUD 上的所有 selector, 这样可以保证该方法不会多次调用。

同时也会保存 HUD 的出现时间。

self.showStarted = [NSDate date]

+ hideHUDForView:animated:

+ (BOOL)hideHUDForView:(UIView *)view animated:(BOOL)animated {
MBProgressHUD *hud = [self HUDForView:view];
if (hud != nil) {
hud.removeFromSuperViewOnHide = YES;
[hud hide:animated];
return YES;
}
return NO;
}

+ hideHUDForView:animated: 方法的实现和 + showHUDAddedTo:animated: 差不多, + HUDForView: 方法会返回对应 view 最上层的 MBProgressHUD 的实例。

+ (MB_INSTANCETYPE)HUDForView:(UIView *)view {
NSEnumerator *subviewsEnum = [view.subviews reverseObjectEnumerator];
for (UIView *subview in subviewsEnum) {
if ([subview isKindOfClass:self]) {
return (MBProgressHUD *)subview;
}
}
return nil;
}

然后调用的 - hide: 方法和 - hideUsingAnimation: 方法也没有什么特别的, 只有在 HUD 隐藏之后 - done 负责隐藏执行 completionBlock 和 delegate 回调。

- (void)done {
[NSObject cancelPreviousPerformRequestsWithTarget:self];
isFinished = YES;
self.alpha = 0.0f;
if (removeFromSuperViewOnHide) {
[self removeFromSuperview];
}
#if NS_BLOCKS_AVAILABLE
if (self.completionBlock) {
self.completionBlock();
self.completionBlock = NULL;
}
#endif
if ([delegate respondsToSelector:@selector(hudWasHidden:)]) {
[delegate performSelector:@selector(hudWasHidden:) withObject:self];
}
}

- showAnimated:whileExecutingBlock:onQueue:completionBlock:

当 block 指定的队列执行时, 显示 HUD, 并在 HUD 消失时, 调用 completion。

同时 MBProgressHUD 也提供一些其他的便利方法实现这一功能:

- (void)showAnimated:(BOOL)animated whileExecutingBlock:(dispatch_block_t)block;
- (void)showAnimated:(BOOL)animated whileExecutingBlock:(dispatch_block_t)block completionBlock:(MBProgressHUDCompletionBlock)completion;
- (void)showAnimated:(BOOL)animated whileExecutingBlock:(dispatch_block_t)block onQueue:(dispatch_queue_t)queue;

该方法会异步在指定 queue 上运行 block 并在 block 执行结束调用 - cleanUp。

- (void)showAnimated:(BOOL)animated whileExecutingBlock:(dispatch_block_t)block onQueue:(dispatch_queue_t)queue
completionBlock:(MBProgressHUDCompletionBlock)completion {
self.taskInProgress = YES;
self.completionBlock = completion;
dispatch_async(queue, ^(void) {
block();
dispatch_async(dispatch_get_main_queue(), ^(void) {
[self cleanUp];
});
});
[self show:animated];
}

关于 - cleanUp 我们会在下一段中介绍。

- showWhileExecuting:onTarget:withObject:

当一个后台任务在新线程中执行时，显示 HUD。

- (void)showWhileExecuting:(SEL)method onTarget:(id)target withObject:(id)object animated:(BOOL)animated {
methodForExecution = method;
targetForExecution = MB_RETAIN(target);
objectForExecution = MB_RETAIN(object);
// Launch execution in new thread
self.taskInProgress = YES;
[NSThread detachNewThreadSelector:@selector(launchExecution) toTarget:self withObject:nil];
// Show HUD view
[self show:animated];
}

在保存 methodForExecution targetForExecution 和 objectForExecution 之后, 会在新的线程中调用方法。

- (void)launchExecution {
@autoreleasepool {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
// Start executing the requested task
[targetForExecution performSelector:methodForExecution withObject:objectForExecution];
#pragma clang diagnostic pop
// Task completed, update view in main thread (note: view operations should
// be done only in the main thread)
[self performSelectorOnMainThread:@selector(cleanUp) withObject:nil waitUntilDone:NO];
}
}

- launchExecution 会创建一个自动释放池, 然后再这个自动释放池中调用方法, 并在方法调用结束之后在主线程执行 - cleanUp。

Trick

在 MBProgressHUD 中有很多神奇的魔法来解决一些常见的问题。

ARC

MBProgressHUD 使用了一系列神奇的宏定义来兼容 MRC。

#ifndef MB_INSTANCETYPE
#if __has_feature(objc_instancetype)
#define MB_INSTANCETYPE instancetype
#else
#define MB_INSTANCETYPE id
#endif
#endif
#ifndef MB_STRONG
#if __has_feature(objc_arc)
#define MB_STRONG strong
#else
#define MB_STRONG retain
#endif
#endif
#ifndef MB_WEAK
#if __has_feature(objc_arc_weak)
#define MB_WEAK weak
#elif __has_feature(objc_arc)
#define MB_WEAK unsafe_unretained
#else
#define MB_WEAK assign
#endif
#endif

通过宏定义 __has_feature 来判断当前环境是否启用了 ARC, 使得不同环境下宏不会出错。

KVO

MBProgressHUD 通过 @property 生成了一系列的属性。

- (NSArray *)observableKeypaths {
return [NSArray arrayWithObjects:@"mode", @"customView", @"labelText", @"labelFont", @"labelColor",
@"detailsLabelText", @"detailsLabelFont", @"detailsLabelColor", @"progress", @"activityIndicatorColor", nil];
}

这些属性在改变的时候不会, 重新渲染整个 view, 我们在一般情况下覆写 setter 方法, 然后再 setter 方法中刷新对应的属性，在 MBProgressHUD 中使用 KVO 来解决这个问题。

- (void)registerForKVO {
for (NSString *keyPath in [self observableKeypaths]) {
[self addObserver:self forKeyPath:keyPath options:NSKeyValueObservingOptionNew context:NULL];
}
}
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
if (![NSThread isMainThread]) {
[self performSelectorOnMainThread:@selector(updateUIForKeypath:) withObject:keyPath waitUntilDone:NO];
} else {
[self updateUIForKeypath:keyPath];
}
}
- (void)updateUIForKeypath:(NSString *)keyPath {
if ([keyPath isEqualToString:@"mode"] || [keyPath isEqualToString:@"customView"] ||
[keyPath isEqualToString:@"activityIndicatorColor"]) {
[self updateIndicators];
} else if ([keyPath isEqualToString:@"labelText"]) {
label.text = self.labelText;
} else if ([keyPath isEqualToString:@"labelFont"]) {
label.font = self.labelFont;
} else if ([keyPath isEqualToString:@"labelColor"]) {
label.textColor = self.labelColor;
} else if ([keyPath isEqualToString:@"detailsLabelText"]) {
detailsLabel.text = self.detailsLabelText;
} else if ([keyPath isEqualToString:@"detailsLabelFont"]) {
detailsLabel.font = self.detailsLabelFont;
} else if ([keyPath isEqualToString:@"detailsLabelColor"]) {
detailsLabel.textColor = self.detailsLabelColor;
} else if ([keyPath isEqualToString:@"progress"]) {
if ([indicator respondsToSelector:@selector(setProgress:)]) {
[(id)indicator setValue:@(progress) forKey:@"progress"];
}
return;
}
[self setNeedsLayout];
[self setNeedsDisplay];
}

- observeValueForKeyPath:ofObject:change:context: 方法中的代码是为了保证 UI 的更新一定是在主线程中, 而 - updateUIForKeypath: 方法负责 UI 的更新