在自动填充后，在UIWebView中执行Javascript后验证Label的长度

为了说明这一点，我将把我的问题分开。

目标：

执行一些Javascript后，检查页面上的a元素ONCE；但如果不正确，我希望按下按钮就能重新检查。

我尝试过的：

        -(IBAction)signin {
    [passwordTF resignFirstResponder];
    [usernameTF resignFirstResponder];
    //create js strings
    NSString *loadUsernameJS = [NSString stringWithFormat:@"var field = document.getElementById('login-form-username'); field.value='%@';", username];
    NSString *loadPasswordJS = [NSString stringWithFormat:@"var field = document.getElementById('login-form-password'); field.value='%@';", password];
    //autofill the form
    [mainWebView stringByEvaluatingJavaScriptFromString:loadUsernameJS];
    [mainWebView stringByEvaluatingJavaScriptFromString:loadPasswordJS];
    //auto login
    [mainWebView stringByEvaluatingJavaScriptFromString:@"document.getElementById('submit-login').click();"];

}
- (void)webViewDidFinishLoad:(UIWebView *)webView {
    NSLog(@"webViewDidiFinishLoad called");
    if (shouldVerify == YES) {
        NSLog(@"webViewDidiFinishLoad - shouldVerify YES");
        NSString *failedLogin = [mainWebView stringByEvaluatingJavaScriptFromString: @"document.getElementById('login-msg')"];
        if ([failedLogin isEqualToString:@"Failed login"]) {
            NSLog(@"webViewDidiFinishLoad - shouldVerify YES - failed");
            UIAlertView *WCE = [[UIAlertView alloc] initWithTitle:@"Wrong Credentials" message:@"The username or password you entered is incorrect please try again." delegate:nil cancelButtonTitle:@"Ok" otherButtonTitles:nil, nil];
            [WCE show];
            [keychainItem resetKeychainItem];
            password = [keychainItem objectForKey:(__bridge id)(kSecValueData)];
            username = [keychainItem objectForKey:(__bridge id)(kSecAttrAccount)];
            [usernameTF setText:username];
            [passwordTF setText:password];

        } else {
            NSLog(@"webViewDidiFinishLoad - shouldVerify YES - success");
            ViewController *viewController = [[UIStoryboard storyboardWithName:@"Main" bundle:nil] instantiateViewControllerWithIdentifier:@"ViewController"];
            UINavigationController *navBar=[[UINavigationController alloc]initWithRootViewController:viewController];
            navBar.navigationBarHidden = YES;
            [self presentViewController:navBar animated:YES completion:nil];
        }
        shouldVerify = NO;
    }
}
- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType {
    if (navigationType == UIWebViewNavigationTypeOther) {
        NSLog(@"shouldStartLoadWithRequest - shouldVerify YES");
        shouldVerify = YES;
    } else {
        NSLog(@"shouldStartLoadWithRequest - shouldVerify NO");
        shouldVerify = NO;
    }
    return YES;
}

问题：

出于某种原因：

if ([failedLogin isEqualToString:@"Failed login"]) {
            NSLog(@"webViewDidiFinishLoad - shouldVerify YES - failed");
            UIAlertView *WCE = [[UIAlertView alloc] initWithTitle:@"Wrong Credentials" message:@"The username or password you entered is incorrect please try again." delegate:nil cancelButtonTitle:@"Ok" otherButtonTitles:nil, nil];
            [WCE show];

        } else {
            NSLog(@"webViewDidiFinishLoad - shouldVerify YES - success");
        }

if语句总是返回false和

  NSLog(@"webViewDidiFinishLoad - shouldVerify YES - success");

在不应该打印的时候被打印出来，failedLogin等于@"Failed Login"。如果我删除else语句，它总是在为true时将If语句验证为虚假登录凭据，这就是为什么我认为在处理它之前，我应该先检查它。

我的猜测：

当webView还没有执行完javascript和/或在点击按钮后重新加载网页时，我正在运行这个if语句。

资源：

我不知道这有什么帮助，但我正在使用的网站是：tapgram.com/login

完整的当前代码可在此处获得：http://pastebin.com/dnCn62FP完整的项目代码请评论，我会添加链接。