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iOS 源代码分析 --- MBProgressHUD

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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。