iOS 源代码分析 --- MBProgressHUD

来源：互联网发布：于正知乎编辑：程序博客网时间：2024/06/06 15:51

[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

```objectivec

+ (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.

```objectivec

- (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.

```objectivec

- (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:`

```objectivec

- (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.

```objectivec

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.

```objectivec

self.showStarted = [NSDate date]

```

### `+ hideHUDForView:animated:`

```objectivec

+ (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.

```objectivec

+ (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.

```objectivec

- (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:

```objectivec

- (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`.

```objectivec

- (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.

```objectivec

- (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`.

```objectivec

#ifndef MB_INSTANCETYPE

#if __has_feature(objc_instancetype)

#define MB_INSTANCETYPE instancetype

#else

#define MB_INSTANCETYPE id

#endif

#ifndef MB_STRONG

#if __has_feature(objc_arc)

#define MB_STRONG strong

#else

#define MB_STRONG retain

#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

```

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.

```objectivec

- (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.

```objectivec

- (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.

## 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.

Follow: [@Draveness](https://github.com/Draveness)

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