Question

我需要更改一个函数来评估从UIWebView到WKWebView的JavaScript。我需要在这个函数中返回求值结果。

现在，我正在打电话：

[wkWebView evaluateJavaScript:call completionHandler:^(NSString *result, NSError *error)
{
    NSLog(@"Error %@",error);
    NSLog(@"Result %@",result);
}];

但是我需要得到像返回值这样的结果，就像在UIWebView中一样。你能建议一个解决方案吗？

Answer 1

更新：这不再适用于iOS 12+。

我通过等待结果直到返回结果值来解决了这个问题。

我使用NSRunLoop等待，但我不确定它的最佳方式......

以下是我现在使用的类别扩展源代码：

@interface WKWebView(SynchronousEvaluateJavaScript)
- (NSString *)stringByEvaluatingJavaScriptFromString:(NSString *)script;
@end

@implementation WKWebView(SynchronousEvaluateJavaScript)

- (NSString *)stringByEvaluatingJavaScriptFromString:(NSString *)script
{
    __block NSString *resultString = nil;
    __block BOOL finished = NO;

    [self evaluateJavaScript:script completionHandler:^(id result, NSError *error) {
        if (error == nil) {
            if (result != nil) {
                resultString = [NSString stringWithFormat:@"%@", result];
            }
        } else {
            NSLog(@"evaluateJavaScript error : %@", error.localizedDescription);
        }
        finished = YES;
    }];

    while (!finished)
    {
        [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
    }

    return resultString;
}
@end

示例代码：

NSString *userAgent = [_webView stringByEvaluatingJavaScriptFromString:@"navigator.userAgent"];

NSLog(@"userAgent: %@", userAgent);

Answer 2

如果javascript的代码引发NSError：

，此解决方案也有效

- (NSString *)stringByEvaluatingJavaScriptFromString:(NSString *)script {
    __block NSString *resultString = nil;
    __block BOOL finished = NO;

    [self evaluateJavaScript:script completionHandler:^(id result, NSError *error) {
        if (error == nil) {
            if (result != nil) {
                resultString = [NSString stringWithFormat:@"%@", result];
            }
        } else {
            NSLog(@"evaluateJavaScript error : %@", error.localizedDescription);
        }
        finished = YES;
    }];

    while (!finished)
    {
        [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
    }

    return resultString;
}

Answer 3

我只是偶然发现了同样的问题并为它写了一个小的Swift（3.0）WKWebView扩展，我想可以分享它：

extension WKWebView {
    func evaluate(script: String, completion: (result: AnyObject?, error: NSError?) -> Void) {
        var finished = false

        evaluateJavaScript(script) { (result, error) in
            if error == nil {
                if result != nil {
                    completion(result: result, error: nil)
                }
            } else {
                completion(result: nil, error: error)
            }
            finished = true
        }

        while !finished {
            RunLoop.current().run(mode: .defaultRunLoopMode, before: Date.distantFuture)
        }
    }
}

Answer 4

基于@ mort3m的答案，这是可与Swift 5一起使用的WKWebView扩展。

extension WKWebView {
    func evaluate(script: String, completion: @escaping (Any?, Error?) -> Void) {
        var finished = false

        evaluateJavaScript(script, completionHandler: { (result, error) in
            if error == nil {
                if result != nil {
                    completion(result, nil)
                }
            } else {
                completion(nil, error)
            }
            finished = true
        })

        while !finished {
            RunLoop.current.run(mode: RunLoop.Mode(rawValue: "NSDefaultRunLoopMode"), before: NSDate.distantFuture)
        }
    }
}

Answer 5

我发现注入的javascript中final语句的值是作为完成函数的id参数传递的返回值，如果没有异常的话。所以，例如：

static MarvinImage memory = new MarvinImage();

Answer 6

仅此有效，以上答案对我无效。

- (NSString *)stringByEvaluatingJavaScriptFromString:(NSString *)script
{
    __block NSString *resultString = nil;
    dispatch_semaphore_t sem = dispatch_semaphore_create(0);
    [self evaluateJavaScript:script completionHandler:^(id result, NSError *error) {
        if (error == nil) {
            if (result != nil) {
                resultString = [NSString stringWithFormat:@"%@", result];
            }
        } else {
            NSLog(@"evaluateJavaScript error : %@", error.localizedDescription);
        }
        dispatch_semaphore_signal(sem);
    }];
    dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER);
    
    return resultString;
}

Answer 7

可以使用调度信号量。它适用于 iOS12 +

示例：

    __block NSString *resultString = nil;
    dispatch_semaphore_t sem = dispatch_semaphore_create(0);
    [self evaluateJavaScript:script completionHandler:^(id result, NSError *error) {
        if (error == nil) {
            if (result != nil) {
                resultString = [NSString stringWithFormat:@"%@", result];
                dispatch_semaphore_signal(sem);
            }
        } else {
            NSLog(@"evaluateJavaScript error : %@", error.localizedDescription);
        }
        finished = YES;
    }];

    dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER);

    //process resultString here.

WKWebView评估JavaScript返回值

7 个答案: