#import "ViewController.h"
#import <WebKit/WebKit.h>

@interface ViewController ()
@property (weak, nonatomic) WKWebView *webView;
@property (weak, nonatomic) CALayer *progresslayer;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    WKWebView *webView = [[WKWebView alloc]initWithFrame:[UIScreen mainScreen].bounds];
    // 添加监听
    [webView addObserver:self forKeyPath:@"estimatedProgress" options:NSKeyValueObservingOptionNew context:nil];
    [webView addObserver:self forKeyPath:@"title" options:NSKeyValueObservingOptionNew context:nil];
    self.webView = webView;
    [self.view addSubview:webView];
    
    self.title = @"加载中...";
    
    //进度条
    UIView *progress = [[UIView alloc]initWithFrame:CGRectMake(0, 64, CGRectGetWidth(self.view.frame), 3)];
    progress.backgroundColor = [UIColor clearColor];
    [self.view addSubview:progress];
    
    CALayer *layer = [CALayer layer];
    layer.frame = CGRectMake(0, 0, 0, 3);
    layer.backgroundColor = [UIColor blueColor].CGColor;
    [progress.layer addSublayer:layer];
    self.progresslayer = layer;
    
    [webView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"http://www.baidu.com"]]];
}

- (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 if ([keyPath isEqualToString:@"title"]) {
        if (object == self.webView) {
            self.title = self.webView.title;
        }
        else {
            [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
        }}
}

- (void)dealloc{
// 移除监听
    [(WKWebView *)self.view removeObserver:self forKeyPath:@"estimatedProgress"];
    [(WKWebView *)self.view removeObserver:self forKeyPath:@"title"];
}

UIWebView可以使用 NJKWebViewProgress进行进度条加载。