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
Objective-C
+ (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);}
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- 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.
Objective-C
- (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;}
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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.
Objective-C
- (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]; }}
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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:
Objective-C
- (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; }}
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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.
Objective-C
typedef NS_ENUM(NSInteger, MBProgressHUDAnimation) { /** Opacity animation */ MBProgressHUDAnimationFade, /** Opacity + scale animation */ MBProgressHUDAnimationZoom, MBProgressHUDAnimationZoomOut = MBProgressHUDAnimationZoom, MBProgressHUDAnimationZoomIn};
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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.
Objective-C
self.showStarted = [NSDate date]
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+ hideHUDForView:animated:
Objective-C
+ (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;}
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+ 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.
Objective-C
+ (MB_INSTANCETYPE)HUDForView:(UIView *)view { NSEnumerator *subviewsEnum = [view.subviews reverseObjectEnumerator]; for (UIView *subview in subviewsEnum) { if ([subview isKindOfClass:self]) { return (MBProgressHUD *)subview; } } return nil;}
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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.
Objective-C
- (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]; }}
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- 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:
Objective-C
- (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;
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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];}
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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.
Objective-C
- (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];}
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在保存 methodForExecution targetForExecution 和 objectForExecution 之后, 会在新的线程中调用方法.
Objective-C
- (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]; }}
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- 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.
Objective-C
#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
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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.
Objective-C
- (NSArray *)observableKeypaths { return [NSArray arrayWithObjects:@"mode", @"customView", @"labelText", @"labelFont", @"labelColor", @"detailsLabelText", @"detailsLabelFont", @"detailsLabelColor", @"progress", @"activityIndicatorColor", nil];}
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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.
Objective-C
- (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];}
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- 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.
End
MBProgressHUD 由于是一个 UI 的第三方库, 所以它的实现还是挺简单的.
本文转载自 Draveness 技术博客。
原文链接：https://draveness.me/ios-yuan-dai-ma-fen-xi-mbprogresshud
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