[TOC]
简介
SVProgressHUB是iOS上的的一款loading轻量级美观的加载框。
首先来看下结构目录
SVIndefiniteAnimatedView 是无限旋转的菊花视图
SVProgressAnimatedView 是进度条视图
SVRadialGradientLayer 是渐变模式下渐变的背景Layer
使用
显示
SVProgressHUD提供了显示加载图便利方法，而且几乎全是类方法，在开发中能方便的使用。如
- showWithStatus 显示加载，并显示文本
- showProgress 显示加载，并展示当前进度条
- showInfoWithStatus 显示使用Info状态的图片的加载框来替代菊花或者进度条
- showSuccessWithStatus 显示success状态的图片（一个勾）的加载框来替代菊花或者进度条
- showErrorWithStatus 显示error状态的图片（一个x）的加载框来替代菊花或者进度条
除此之外你也可以设置自己的图片，使用+ (void)showImage:(UIImage*)image status:(NSString*)status;
消失
SVProgressHUD提供了几种方式来显示一个Loding框
- dismiss 直接关闭一个加载Hub
- dismissWithDelay 延迟关闭一个Hub
- dismissWithCompletion 关闭Hub带一个完成的Block
- dismissWithDelay:completion 延迟关闭Hub并带一个完成的Block
可以看出SVProgressHUD提供了简单明了的API，使用便利的类方法让我们快速在代码中使用
深入源码
显示过程
SVProgressHUD 比较简单易懂
在众多的类方法下面，也实现相应的实例方法
//简单版本
- (void)setStatus:(NSString*)status;
- (void)setFadeOutTimer:(NSTimer*)timer;
- (void)registerNotifications;
- (NSDictionary*)notificationUserInfo;
- (void)positionHUD:(NSNotification*)notification;
- (void)moveToPoint:(CGPoint)newCenter rotateAngle:(CGFloat)angle;
- (void)overlayViewDidReceiveTouchEvent:(id)sender forEvent:(UIEvent*)event;
- (void)showProgress:(float)progress status:(NSString*)status;
- (void)showImage:(UIImage*)image status:(NSString*)status duration:(NSTimeInterval)duration;
- (void)showStatus:(NSString*)status;
- (void)dismiss;
- (void)dismissWithDelay:(NSTimeInterval)delay completion:(SVProgressHUDDismissCompletion)completion;
@end
如何将Hub展示到屏幕上，首先我们从showWithStatus方法往里看。
内部实现
+ (void)showWithStatus:(NSString*)status {
[self sharedView];
[self showProgress:SVProgressHUDUndefinedProgress status:status];
}
在内部实现了一个单例，这也不难理解为什么可以在内方法中快速的显示一个Hub
+ (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;
}
之后使用这个单例视图来完成Hub的显示，那么showProgress这个方法又做什么呢？首先我们看下简化版代码
- (void)showProgress:(float)progress status:(NSString*)status {
__weak SVProgressHUD *weakSelf = self;
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
__strong SVProgressHUD *strongSelf = weakSelf;
if(strongSelf){
//更新视图层级，将SV放到当前window最前面
[strongSelf updateViewHierachy];
//判断如果是进度条，使用进度条View
if(progress >= 0) {
// Add ring to HUD and set progress
[strongSelf.hudView addSubview:strongSelf.ringView];
[strongSelf.hudView addSubview:strongSelf.backgroundRingView];
strongSelf.ringView.strokeEnd = progress;
} else {
// 使用无限旋转的菊花模式
[strongSelf.hudView addSubview:strongSelf.indefiniteAnimatedView];
}
// Show
[strongSelf showStatus:status];
}
}];
}
可以看出，SV为了将显示操作放到主线程使用了[NSOperationQueue mainQueue]来确保在主线程操作UI，
在updateViewHierachy方法中，SV会寻找提供Hub显示的Window，并且将自己添加到上面。使用手法为:
NSEnumerator *frontToBackWindows = [UIApplication.sharedApplication.windows reverseObjectEnumerator];
for (UIWindow *window in frontToBackWindows) {
BOOL windowOnMainScreen = window.screen == UIScreen.mainScreen;
BOOL windowIsVisible = !window.hidden && window.alpha > 0;
BOOL windowLevelNormal = window.windowLevel == UIWindowLevelNormal;
if(windowOnMainScreen && windowIsVisible && windowLevelNormal) {
[window addSubview:self.overlayView];
break;
}
}
找出当前的windowLevelNormal,并且是显示的UI，将自己显示在其之上，但是也有点缺点，就是如果需要在自定义的window上面显示Hub将无能为力。
找到window之后，生成菊花或者进度条View，然后设置label，计算出大小，然后完成显示
动画的绘制
SVIndefiniteAnimatedView是无限旋转的View。其中使用CASharpLayer和LayerMask来完成一个旋转动画，使用一张渐变的图片，设置其mask属性，然后加上旋转动画，来形成一个漂亮的加载动画
动画绘制代码
UIBezierPath* smoothedPath = [UIBezierPath bezierPathWithArcCenter:arcCenter radius:self.radius startAngle:(CGFloat) (M_PI*3/2) endAngle:(CGFloat) (M_PI/2+M_PI*5) clockwise:YES];
_indefiniteAnimatedLayer = [CAShapeLayer layer];
_indefiniteAnimatedLayer.contentsScale = [[UIScreen mainScreen] scale];
_indefiniteAnimatedLayer.frame = CGRectMake(0.0f, 0.0f, arcCenter.x*2, arcCenter.y*2);
_indefiniteAnimatedLayer.fillColor = [UIColor clearColor].CGColor;
_indefiniteAnimatedLayer.strokeColor = self.strokeColor.CGColor;
_indefiniteAnimatedLayer.lineWidth = self.strokeThickness;
_indefiniteAnimatedLayer.lineCap = kCALineCapRound;
_indefiniteAnimatedLayer.lineJoin = kCALineJoinBevel;
_indefiniteAnimatedLayer.path = smoothedPath.CGPath;
CALayer *maskLayer = [CALayer layer];
NSBundle *bundle = [NSBundle bundleForClass:[SVProgressHUD class]];
NSURL *url = [bundle URLForResource:@"SVProgressHUD" withExtension:@"bundle"];
NSBundle *imageBundle = [NSBundle bundleWithURL:url];
NSString *path = [imageBundle pathForResource:@"angle-mask" ofType:@"png"];
maskLayer.contents = (__bridge id)[[UIImage imageWithContentsOfFile:path] CGImage];
maskLayer.frame = _indefiniteAnimatedLayer.bounds;
_indefiniteAnimatedLayer.mask = maskLayer;
NSTimeInterval animationDuration = 1;
CAMediaTimingFunction *linearCurve = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"transform.rotation"];
animation.fromValue = (id) 0;
animation.toValue = @(M_PI*2);
animation.duration = animationDuration;
animation.timingFunction = linearCurve;
animation.removedOnCompletion = NO;
animation.repeatCount = INFINITY;
animation.fillMode = kCAFillModeForwards;
animation.autoreverses = NO;
[_indefiniteAnimatedLayer.mask addAnimation:animation forKey:@"rotate"];
CAAnimationGroup *animationGroup = [CAAnimationGroup animation];
animationGroup.duration = animationDuration;
animationGroup.repeatCount = INFINITY;
animationGroup.removedOnCompletion = NO;
animationGroup.timingFunction = linearCurve;
CABasicAnimation *strokeStartAnimation = [CABasicAnimation animationWithKeyPath:@"strokeStart"];
strokeStartAnimation.fromValue = @0.015;
strokeStartAnimation.toValue = @0.515;
CABasicAnimation *strokeEndAnimation = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
strokeEndAnimation.fromValue = @0.485;
strokeEndAnimation.toValue = @0.985;
animationGroup.animations = @[strokeStartAnimation, strokeEndAnimation];
[_indefiniteAnimatedLayer addAnimation:animationGroup forKey:@"progress"];
圆环动画比较简单，原理是使用CAShareLayer，并且设置的endPath来完成一个由progress驱动的进度条动画
CGPoint arcCenter = CGPointMake(self.radius+self.strokeThickness/2+5, self.radius+self.strokeThickness/2+5);
UIBezierPath* smoothedPath = [UIBezierPath bezierPathWithArcCenter:arcCenter radius:self.radius startAngle:(CGFloat)-M_PI_2 endAngle:(CGFloat) (M_PI + M_PI_2) clockwise:YES];
_ringAnimatedLayer = [CAShapeLayer layer];
_ringAnimatedLayer.contentsScale = [[UIScreen mainScreen] scale];
_ringAnimatedLayer.frame = CGRectMake(0.0f, 0.0f, arcCenter.x*2, arcCenter.y*2);
_ringAnimatedLayer.fillColor = [UIColor clearColor].CGColor;
_ringAnimatedLayer.strokeColor = self.strokeColor.CGColor;
_ringAnimatedLayer.lineWidth = self.strokeThickness;
_ringAnimatedLayer.lineCap = kCALineCapRound;
_ringAnimatedLayer.lineJoin = kCALineJoinBevel;
_ringAnimatedLayer.path = smoothedPath.CGPath;
消失过程
消失调用的是dismissWithDelay:completion方法
消失过程和显示过程相反，大致是
- 在mainQueue中添加一个Block的operation（在主线程更改UI）
- 将自己从SuperView中删除，
- 如果指定了延迟，那么设置一个timer
- 在消失中如果指定动画，那么加一个fade的动画来进行消失
小结
- SV将View添加到Window上
- SV使用NSOperationQueue 来确保自己在主线程修改UI
- SV的动画使用layer来绘制
优点：API简单明了，调用方便
缺点：默认在APP的UIWindow，不好定制
