iOS-正确获取UIWebView的JSContext

前言java

iOS7后苹果开发的JavaScriptCore框架，方便开发者原生逻辑与JS逻辑交互，可是苹果并无开放获取JSContext环境对象的方法，以前都是经过KVC的方式获取JSContext环境对象，[webView valueForKeyPath:@"documentView.webView.mainFrame.javaScriptContext"]。本文是借鉴UIWebView+TS_JavaScriptContext第三方库，并提出本身的一些见解或者说是想法吧。git

JavaScript和Objective-C交互存在的深坑github

（1）内存管理，使用JSExport协议注入对象，会形成强引用；web

（2）还有就是何时注入对象是正确的；具体的缘由参考这篇文章；网络

（3）其实还有一点须要注意，JavaScript方法调用原生OC的方法是在子线程中执行的，若涉及UI逻辑，请自行切换至主线程操做。框架

可是，UIWebView+TS_JavaScriptContext的逻辑中使用了苹果私有API，parentFrame，致使采用此方法获取JSContext的应用被拒绝上架，所以我去掉原有的frame的判断。async

#import <UIKit/UIKit.h>
#import <JavaScriptCore/JavaScriptCore.h>

@protocol DYLWebViewDelegate <UIWebViewDelegate>

@optional
- (void)webView:(UIWebView *)webView didCreateJavaScriptContext:(JSContext *)ctx;

@end

@interface UIWebView (JavaScriptContext)

@property (strong, nonatomic, readonly) JSContext *javaScriptContext;

@end



#import "UIWebView+JavaScriptContext.h"
#import <objc/runtime.h>

@interface UIWebView (DYL_JavaScriptCore_Private)

- (void)dyl_didCreateJavaScriptContext:(JSContext *)dyl_javaScriptContext;

@end

static NSHashTable *g_webViews = nil;
static const void *kStorageJavaScriptContext = @"kStorageJavaScriptContext";

@implementation NSObject (JavaScriptContext)

- (void)webView:(id)unused didCreateJavaScriptContext:(JSContext *)ctx forFrame:(id)frame
{
    void (^notifyDidCreateJavaScriptContext)() = ^{
        for (UIWebView *webView in g_webViews) {
            
            NSString *identifier = [NSString stringWithFormat:@"ts_jscWebView_%lu", (unsigned long)webView.hash];
            [webView stringByEvaluatingJavaScriptFromString:[NSString stringWithFormat:@"var %@ = '%@'", identifier, identifier]];
            
            if ([ctx[identifier].toString isEqualToString:identifier]) {
                [webView dyl_didCreateJavaScriptContext:ctx];
                return ;
            }
        }
    };
    
    if ([NSThread mainThread]) {
        notifyDidCreateJavaScriptContext();
    }
    else {
        dispatch_async(dispatch_get_main_queue(), notifyDidCreateJavaScriptContext);
    }
}

@end


@implementation UIWebView (JavaScriptContext)

+ (id)allocWithZone:(struct _NSZone *)zone {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        g_webViews = [NSHashTable weakObjectsHashTable];
    });
    
    id webView = [super allocWithZone:zone];
    [g_webViews addObject:webView];
    
    return webView;
}

- (void)dyl_didCreateJavaScriptContext:(JSContext *)dyl_javaScriptContext
{
    objc_setAssociatedObject(self, kStorageJavaScriptContext, dyl_javaScriptContext, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    if ([self.delegate respondsToSelector:@selector(webView:didCreateJavaScriptContext:)]) {
        id<DYLWebViewDelegate> delegate = (id<DYLWebViewDelegate>)self.delegate;
        [delegate webView:self didCreateJavaScriptContext:dyl_javaScriptContext];
    }
}

- (JSContext *)javaScriptContext
{
    return objc_getAssociatedObject(self, kStorageJavaScriptContext);
}

@end

最后ide

网络上没有查找到如何规避使用WebFrame的parentFrame私有API的方法，所以不得不去掉原有第三方中的逻辑判断，本文所写的代码也还未运用至实际项目开发，所以我会在新版项目中尝试使用。atom