当我们在请求网络时加载页面时有个动作效果，效果如下：

源代码可以网上找开源项目Coding.net，上面的效果原理为两张图片组合，外面那个则为动画转动，里面的图标则是透明度的变化；主要代码如下：

1：把它封装在EaseLoadingView里面

@interface EaseLoadingView : UIView
@PRoperty (strong, nonatomic) UIImageView *loopView, *monkeyView;
@property (assign, nonatomic, readonly) BOOL isLoading;
- (void)startAnimating;
- (void)stopAnimating;
@end

@interface EaseLoadingView ()
@property (nonatomic, assign) CGFloat loopAngle, monkeyAlpha, angleStep, alphaStep;
@end


@implementation EaseLoadingView

- (instancetype)initWithFrame:(CGRect)frame{
    self = [super initWithFrame:frame];
    if (self) {
        self.backgroundColor = [UIColor clearColor];
        _loopView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"loading_loop"]];
        _monkeyView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"loading_monkey"]];
        [_loopView setCenter:self.center];
        [_monkeyView setCenter:self.center];
        [self addSubview:_loopView];
        [self addSubview:_monkeyView];
        [_loopView mas_makeConstraints:^(MASConstraintMaker *make) {
            make.center.equalTo(self);
        }];
        [_monkeyView mas_makeConstraints:^(MASConstraintMaker *make) {
            make.center.equalTo(self);
        }];
        
        _loopAngle = 0.0;
        _monkeyAlpha = 1.0;
        _angleStep = 360/3;
        _alphaStep = 1.0/3.0;
    }
    return self;
}

- (void)startAnimating{
    self.hidden = NO;
    if (_isLoading) {
        return;
    }
    _isLoading = YES;
    [self loadingAnimation];
}

- (void)stopAnimating{
    self.hidden = YES;
    _isLoading = NO;
}

- (void)loadingAnimation{
    static CGFloat duration = 0.25f;
    _loopAngle += _angleStep;
    if (_monkeyAlpha >= 1.0 || _monkeyAlpha <= 0.0) {
        _alphaStep = -_alphaStep;
    }
    _monkeyAlpha += _alphaStep;
    [UIView animateWithDuration:duration delay:0.0 options:UIViewAnimationOptionCurveLinear animations:^{
        CGAffineTransform loopAngleTransform = CGAffineTransformMakeRotation(_loopAngle * (M_PI / 180.0f));
        _loopView.transform = loopAngleTransform;
        _monkeyView.alpha = _monkeyAlpha;
    } completion:^(BOOL finished) {
        if (_isLoading && [self superview] != nil) {
            [self loadingAnimation];
        }else{
            [self removeFromSuperview];

            _loopAngle = 0.0;
            _monkeyAlpha = 1,0;
            _alphaStep = ABS(_alphaStep);
            CGAffineTransform loopAngleTransform = CGAffineTransformMakeRotation(_loopAngle * (M_PI / 180.0f));
            _loopView.transform = loopAngleTransform;
            _monkeyView.alpha = _monkeyAlpha;
        }
    }];
}

@end

注意loadingAnimation这里面有动作的处理及透明度的处理，当停止加载后把它自个从当前的视图去除；

2：UIView (Common)在UIView扩展类里

#pragma mark LoadingView
@property (strong, nonatomic) EaseLoadingView *loadingView;
- (void)beginLoading;
- (void)endLoading;
@end

- (void)setLoadingView:(EaseLoadingView *)loadingView{
    [self willChangeValueForKey:@"LoadingViewKey"];
    objc_setAssociatedObject(self, &LoadingViewKey,
                             loadingView,
                             OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    [self didChangeValueForKey:@"LoadingViewKey"];
}
- (EaseLoadingView *)loadingView{
    return objc_getAssociatedObject(self, &LoadingViewKey);
}

- (void)beginLoading{
    for (UIView *aView in [self.blankPageContainer subviews]) {
        if ([aView isKindOfClass:[EaseBlankPageView class]] && !aView.hidden) {
            return;
        }
    }
    
    if (!self.loadingView) { //初始化LoadingView
        self.loadingView = [[EaseLoadingView alloc] initWithFrame:self.bounds];
    }
    [self addSubview:self.loadingView];
    [self.loadingView mas_makeConstraints:^(MASConstraintMaker *make) {
        make.self.edges.equalTo(self);
    }];
    [self.loadingView startAnimating];
}

- (void)endLoading{
    if (self.loadingView) {
        [self.loadingView stopAnimating];
    }
}

注意：cocoa的KVO模型中，有两种通知观察者的方式，自动通知和手动通知。顾名思义，自动通知由cocoa在属性值变化时自动通知观察者，而手动通知需要在值变化时调用 willChangeValueForKey:和didChangeValueForKey: 方法通知调用者。

3：使用页面调用

- (void)sendRequest{
    [self.view beginLoading];
    __weak typeof(self) weakSelf = self;
    [[Coding_NetAPIManager sharedManager] request_CodeFile:_myCodeFile withPro:_myProject andBlock:^(id data, NSError *error) {
        [weakSelf.view endLoading];
        if (data) {
            weakSelf.myCodeFile = data;
            [weakSelf refreshCodeViewData];
        }
        [weakSelf.view configBlankPage:EaseBlankPageTypeView hasData:(data != nil) hasError:(error != nil) reloadButtonBlock:^(id sender) {
            [weakSelf sendRequest];
        }];
    }];
}

其中[self.view beginLoading]跟[weakSelf.view endLoading]就可以调用动画效果；

补充：另一种是有很多不同的图片组成的动画效果，可以用每一张图片然后FOR遍历组成出动作效果；

    //设置普通状态的动画图片
    NSMutableArray *idleImages = [NSMutableArray array];
    for (NSUInteger i = 1; i<=60; ++i) {
               UIImage *image = [UIImage imageNamed:[NSString stringWithFormat:@"dropdown_anim__000%zd",i]];
               [idleImages addObject:image];
        [idleImages addObject:image];
    }