WKWebView 进度条

@property (nonatomic) WKWebView *webView;
@property (nonatomic) CALayer *progresslayer;

//创建webView之后监听estimatedProgress属性
_webView = [[WKWebView alloc]initWithFrame:self.view.bounds];
    //就是当前网页加载的进度，所以首先监听这个属性。-> estimatedProgress
    [_webView addObserver:self forKeyPath:@"estimatedProgress" options:NSKeyValueObservingOptionNew context:nil];

    UIView *progress = [[UIView alloc]initWithFrame:CGRectMake(0, 64, CGRectGetWidth(self.view.frame), 3)];
    progress.backgroundColor = [UIColor clearColor];
    [self.view addSubview:progress];
    //隐式动画
    CALayer *layer = [CALayer layer];
    layer.frame = CGRectMake(0, 0, 0, 3);
    layer.backgroundColor = TEXTCOLOR.CGColor;
    [progress.layer addSublayer:layer];
    self.progresslayer = layer;
//监听的方法
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context {
    if ([keyPath isEqualToString:@"estimatedProgress"]) {
        self.progresslayer.opacity = 1;
        if ([change[@"new"] floatValue] < [change[@"old"] floatValue]) {
            return;
        }
        self.progresslayer.frame = CGRectMake(0, 0, self.view.bounds.size.width * [change[@"new"] floatValue], 3);
        if ([change[@"new"] floatValue] == 1) {
            dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(.4 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
                self.progresslayer.opacity = 0;
            });
            dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(.5 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
                self.progresslayer.frame = CGRectMake(0, 0, 0, 3);
            });
        }
    } else {
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
}
//移除监听
- (void)dealloc {

    [_webView removeObserver:self forKeyPath:@"estimatedProgress"];
}