WKWebView踩坑飘过

替换WKWebView的原因有：

内存占用少

项目h5较多，发现当有高清图或gif时在4s上crash较多，几乎都是内存原因。WKWebView占用内存较少，立马简单的测试下，原本必挂的网页运行正常，决定换。

#import <WebKit/WebKit.h>
- (void)viewDidLoad {
    [super viewDidLoad];
    WKWebViewConfiguration *config = [[WKWebViewConfiguration alloc] init];
    config.userContentController = [[WKUserContentController alloc] init];
    self.webView = [[WKWebView alloc] initWithFrame:self.view.bounds configuration:config];
    [self.view addSubview:_webView];
    NSString *htmlPath = [[NSBundle mainBundle] pathForResource:@"test" ofType:@"html"];
    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL fileURLWithPath:htmlPath]];
    [_webView loadRequest:request];
    ...
}

进度容易获取，无需引用第三方框架

首先看下，WKWebView的estimatedProgress属性注解

/*! @abstract An estimate of what fraction of the current navigation has been completed.
 @discussion This value ranges from 0.0 to 1.0 based on the total number of
 bytes expected to be received, including the main document and all of its
 potential subresources. After a navigation completes, the value remains at 1.0
 until a new navigation starts, at which point it is reset to 0.0.
 @link WKWebView @/link is key-value observing (KVO) compliant for this
 property.
 */

注册通知：

- (void)viewDidLoad
    [super viewDidLoad];
    ...
    [self.webView addObserver:self forKeyPath:@"estimatedProgress" options:NSKeyValueObservingOptionNew context:nil];
}

响应，progressView用的是开源的NJKWebViewProgressView：

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    if (object == self.webView && [keyPath isEqualToString:@"estimatedProgress"]) {
        CGFloat newprogress = [[change objectForKey:NSKeyValueChangeNewKey] doubleValue];
        GTRWeakSelf
        dispatch_async(dispatch_get_main_queue(), ^{
            [weakSelf.webViewProgressView setProgress:newprogress animated:YES];
        });
        
    }
}

移除：

- (void)dealloc {
    [_webView removeObserver:self forKeyPath:@"estimatedProgress"];
}

js与native通讯方式多样化，和android统一，但不支持javascript core

1、js使用alert、prompt和confirm等方式，wkwebview用

native:
#pragma mark - WKUIDelegate
- (void)webView:(WKWebView *)webView runJavaScriptAlertPanelWithMessage:(NSString *)message initiatedByFrame:(WKFrameInfo *)frame completionHandler:(void (^)(void))completionHandler
{
    
    UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"提醒" message:message preferredStyle:UIAlertControllerStyleAlert];
    [alert addAction:[UIAlertAction actionWithTitle:@"知道了" style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {
        completionHandler();
    }]];
    
    [self presentViewController:alert animated:YES completion:nil];
}

2、URL方式，如果地址是网络上，可把html放到本地可解决

js:
<script language="javascript">
            function loadURL(url) {
                var iFrame;
                iFrame = document.createElement("iframe");
                iFrame.setAttribute("src", url);
                iFrame.setAttribute("style", "display:none;");
                iFrame.setAttribute("height", "0px");
                iFrame.setAttribute("width", "0px");
                iFrame.setAttribute("frameborder", "0");
                document.body.appendChild(iFrame);
                // 发起请求后这个iFrame就没用了，所以把它从dom上移除掉
                iFrame.parentNode.removeChild(iFrame);
                iFrame = null;
            }
            function getVersion() {
                loadURL("gtrAction://getVersion");
            }
</script>

native:
#pragma mark - WKNavigationDelegate
- (void)webView:(WKWebView *)webView decidePolicyForNavigationAction:(WKNavigationAction *)navigationAction decisionHandler:(void (^)(WKNavigationActionPolicy))decisionHandler
{
    NSURL *URL = navigationAction.request.URL;
    NSString *scheme = [URL scheme];
    if ([scheme isEqualToString:@"haleyaction"]) {
        
        [self handleCustomAction:URL];
        
        decisionHandler(WKNavigationActionPolicyCancel);
        return;
    }
    decisionHandler(WKNavigationActionPolicyAllow);
}

3、用MessageHandler方式，我们选择这种方式实现。

js实现：
 window.webkit.messageHandlers.<name>.postMessage(<messageBody>)
native实现祥见集成问题实现。

集成问题

WKWebView使用有循环引用，原因是UIViewController->WKWebView->WKWebViewConfiguration->WKUserContentController，最后WKUserContentController在addScriptMessageHandler:name:又引用UIViewController。

有2个解决方案：

1、这种方式简单，只需在viewWillAppear和viewWillDisappear相应的添加和删除messageHandler。不过部分系统上再次addScriptMessageHandler无效。

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
     [self.webView.configuration.userContentController addScriptMessageHandler:self name:@"getVersion"];
}

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    [_webView.configuration.userContentController removeScriptMessageHandlerForName:@"getVersion"];
}
- (void)dealloc {
    DebugLog(@"GTRViewController dealloc");
}

2、打破addScriptMessageHandler这个循环引用，用中间代理方式实现。

GTRWeakScriptMessageDelegate.h

#import <Foundation/Foundation.h>
#import <WebKit/WebKit.h>

@protocol GTRWeakScriptMessageDelegate <NSObject>
- (void)getVersion;
@end

@interface GTRWeakScriptMessageDelegate : NSObject <WKScriptMessageHandler>
@property (nonatomic, weak) id <GTRWeakScriptMessageDelegate> gDelegate;

- (instancetype)initWithDelegate:(id <GTRWeakScriptMessageDelegate>)delegate;
@end

GTRWeakScriptMessageDelegate.m

#import "GTRWeakScriptMessageDelegate.h"

@interface GTRWeakScriptMessageDelegate () 

@end

@implementation GTRWeakScriptMessageDelegate

- (instancetype)initWithDelegate:(id <GTRWeakScriptMessageDelegate>)delegate {
    self = [super init];
    if (self) {
        self.gDelegate = delegate;
    }
    return self;
}

- (void)userContentController:(WKUserContentController *)userContentController didReceiveScriptMessage:(WKScriptMessage *)message {
    
    if (![self.gDelegate conformsToProtocol:@protocol(GTRWeakScriptMessageDelegate)]) {
        return;
    }
    
    if ([message.name isEqualToString:@"getVersion"]) {
        //异步回掉
        [self.gDelegate getVersion];
    }
}

- (void)dealloc {
    DebugLog(@"GTRWeakScriptMessageDelegate dealloc");
}

@end

GTRViewController.m

@property (nonatomic, strong) GTRWeakScriptMessageDelegate *weakScriptDelegate;
- (void)viewDidLoad {
    [super viewDidload];
    _weakScriptDelegate = [[GTRWeakScriptMessageDelegate alloc] initWithDelegate:self];
    
    WKWebViewConfiguration *config = [[WKWebViewConfiguration alloc] init];
    config.userContentController = [[WKUserContentController alloc] init];
    
    _webView = [[WKWebView alloc] initWithFrame:self.view.bounds configuration:config];
    //添加messageHandler
    [_webView.configuration.userContentController addScriptMessageHandler:self.weakScriptDelegate name:@"getVersion"];
    
    _webView.scrollView.delegate = self;
    _webView.navigationDelegate = self;
    _webView.UIDelegate = self;
    [self.view addSubview:_webView];
}

- (void)dealloc {
    [_webView.configuration.userContentController removeScriptMessageHandlerForName:@"getVersion"];
    [_webView removeObserver:self forKeyPath:@"estimatedProgress"];
    _webView.UIDelegate = nil;
    _webView.navigationDelegate = nil;
    _webView.scrollView.delegate = nil;
    DebugLog(@"GTRViewController dealloc");
}

附送wkwebview修改Agent，用来标示是应用内web，ios9后用setCustomUserAgent:方法.

AppDelegate.m

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    ...
    UIWebView *webView = [[UIWebView alloc] initWithFrame:CGRectZero];
    NSString *userAgent = [webView stringByEvaluatingJavaScriptFromString:@"navigator.userAgent"];
    NSString *newUserAgent = [userAgent stringByAppendingString:@" ua gtr_demo"];//自定义需要拼接的字符串
    NSDictionary *dictionary = [NSDictionary dictionaryWithObjectsAndKeys:newUserAgent, @"UserAgent", nil];
    [[NSUserDefaults standardUserDefaults] registerDefaults:dictionary];
    [[NSUserDefaults standardUserDefaults] synchronize];
}

GTRViewController.m
- (void)viewDidLoad {
    ...
    [self.webView evaluateJavaScript:@"navigator.userAgent" completionHandler:^(id result, NSError *error) {
        DebugLog(@"Webview UserAgent:%@", result);
    }];
    ...
}