How to get data from the block function?

Question

I trigger a js from a WKWebView and get the result in the block function. In the block function, I got the correct data. However, when I assign this data to the external variable outside, I always get nil value.

- (id)triggerJS:(NSString*)js
{
    NSLog(@"JS = %@",js);

    __block id resultJS = nil;
    [self.webView evaluateJavaScript:js completionHandler: ^(id data, NSError* err) {

                                                            resultJS = [data copy];
                                                        }
     ];

    if (resultJS != nil)
    {
        NSString* str = (NSString*)resultJS;
        NSLog(@"Result of JS = %@", str);
    }
    else
    {
        NSLog(@"Result of JS = nil");
    }

    return resultJS;
}

Why is that? Thanks.

JERC JERC · Accepted Answer · 2015-03-25T16:42:14

That is because the function evaluateJavaScript is executed asynchronous way, so when you execute the if (resultJS != nil) the "completionHandler" is not executed yet, thats the reason that you always get nil value.

The best improvement for this, is trying to re-write and adapt your code inside the "completionHandler" block, that will manage the resultJS data.

How to get data from the block function?

1 Answers