有一个API可直接从Objective-C调用JavaScript， 但不能直接从Javascript调用Objective-C。

如何告诉您的Objective-C代码通过WebView中的Java脚本执行某些操作

您必须将Javascript操作序列化为一个特殊的URL，并在UIWebView的委托shouldStartLoadWithRequest方法中截取该URL
。

- (BOOL)webView:(UIWebView *)webView
        shouldStartLoadWithRequest:(NSURLRequest *)request
                    navigationType:(UIWebViewNavigationType)navigationType;

在这里，您可以反序列化该特殊URL并对其进行解释，以实现Objective-
C方面的目标。（您应该返回NO上述shouldStartLoadWithRequest方法，以便UIWebView不会使用您的虚假URL实际发出HTTP请求来加载网页。）

如何从Objective-C运行Javascript代码

然后，您可以通过在Webview上调用此方法来从Objective-C运行Javascript。

- (NSString *)stringByEvaluatingJavaScriptFromString:(NSString *)script;

范例程式码

我建议使用伪造的URL方案，这样很容易分辨出操作URL和合法请求之间的区别。您可以按照以下方式在Javascript中发出此请求：

// JavaScript to send an action to your Objective-C code
var myAppName = 'myfakeappname';
var myActionType = 'myJavascriptActionType';
var myActionParameters = {}; // put extra info into a dict if you need it

// (separating the actionType from parameters makes it easier to parse in ObjC.)
var jsonString = (JSON.stringify(myActionParameters));
var escapedJsonParameters = escape(jsonString);
var url = myAppName + '://' + myActionType + "#" + escapedJsonParameters;
document.location.href = url;

然后，在UIWebView.delegate的shouldStartLoadWithRequest方法中，您可以检查URL方案和片段，以检查这是正常请求还是您的特殊操作之一。（URL的片段位于后面#。）

- (BOOL)webView:(UIWebView *)webView
        shouldStartLoadWithRequest:(NSURLRequest *)request
                    navigationType:(UIWebViewNavigationType)navigationType {

    // these need to match the values defined in your JavaScript
    NSString *myAppScheme = @"myfakeappname";
    NSString *myActionType = @"myJavascriptActionType";

    // ignore legit webview requests so they load normally
    if (![request.URL.scheme isEqualToString:myAppScheme]) {
        return YES;
    }

    // get the action from the path
    NSString *actionType = request.URL.host;
    // deserialize the request JSON
    NSString *jsonDictString = [request.URL.fragment stringByReplacingPercentEscapesUsingEncoding:NSASCIIStringEncoding];

    // look at the actionType and do whatever you want here
    if ([actionType isEqualToString:myActionType]) {
        // do something in response to your javascript action
        // if you used an action parameters dict, deserialize and inspect it here
    }


    // make sure to return NO so that your webview doesn't try to load your made-up URL
    return NO;
}