将Javascript变量传递给Objective-C
我已经在这里看到了如何将Objective-C变量传递给JavaScript，将目标c变量传递给ios中的javascript ，但是当我使用这样的东西时，如何将变量从JavaScript传递给Objective-C：
I've seen how to pass an Objective-C variable to JavaScript right here, passing objective c variable to javascript in ios, but how do I pass a variable from JavaScript to Objective-C when I'm using something like this:
[webView stringByEvaluatingJavaScriptFromString：@var elems = document.body.getElementsByTagName（\u\）;
passThisVarToObjC = elems.length;
嗯，这就是我们的意思拨打字符串键入。
Well, this is what we call stringly typed.
因为 stringByEvaluatingJavaScriptFromString：的返回类型是 NSString * ，您将需要坚持使用字符串或将值强制转换为其他（读取：更可用的）类型。
Because the return type of stringByEvaluatingJavaScriptFromString: is NSString *, you will either need to stick to using a string or coercing the value into some other (read:more usable) type.
但无论如何， stringByEvaluatingJavaScriptFromString：会毫无问题地返回JavaScript变量的值。
But anyway, stringByEvaluatingJavaScriptFromString: will return the value of a JavaScript variable to you without a problem.
这样做的方法是使用匿名函数（在这种情况下是自动执行）：
The way this is accomplished is through the use of an anonymous function (which in this case is self-executing):
NSString *numOfElements = [webView stringByEvaluatingJavaScriptFromString:@"(function() {var elems = document.body.getElementsByTagName(\"u\"); return elems.length;})();"];
//do normal stuff with numOfElements like cast to an int or something cool like that.