iOS開發 --- UIWebView OC調用JS方法

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    self.navigationItem.title = @"活動詳情頁面";
    self.backButton.frame = CGRectMake(0, 0, 66, 44);
    [self.backButton setTitle:@"關閉" forState:UIControlStateNormal];
    [self.backButton setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];
    
    [self addWebView];
    
}

添加WebView

-(void)addWebView{
    self.webView = [[UIWebView alloc]initWithFrame:CGRectMake(0, StatusAndNaviHeight, SCREEN_WIDTH, SCREEN_HEIGHT - StatusAndNaviHeight -iPhoneXSafeBottomMargin)];
    _webView.delegate = self;
    _webView.scalesPageToFit = YES;
    NSString *url = [OnlineServiceUrl stringByAppendingFormat:@"?tk=%@&ut=%@",[userDefa valueForKey:@"AppKey"],self.userTokenStr];
    //加載請求的時候忽略緩存
    NSURLRequest *request  = [NSURLRequest requestWithURL:[NSURL URLWithString:url] cachePolicy:NSURLRequestReloadIgnoringLocalCacheData timeoutInterval:5.0];

    [_webView loadRequest:request];
    [self.view addSubview:_webView];
}

左上角返回按鈕點擊方法實現

-(void)leftButAction{

    NSString *jsStr = [NSString stringWithFormat:@"%@",@"isShowAlertView()"];
    NSString *result = [self.webView stringByEvaluatingJavaScriptFromString:jsStr];
    //js返回0：js控制跳出彈框 1：返回上級頁面
    NSLog(@"jsStr:%@",result);
    
    if ([result intValue] == 1) {
        [self.navigationController popViewControllerAnimated:YES];
    }
}

注意：

stringByEvaluatingJavaScriptFromString 這個方法只能在主線程調用！！！

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);  
dispatch_async(queue, ^{  
    [webView stringByEvaluatingJavaScriptFromString:@"aaa"];
});
//崩潰信息
Tried to obtain the web lock from a thread other than the main thread or the web thread. 
This may be a result of calling to UIKit from a secondary thread. Crashing now...
崩潰產生的原因是你在主線程以外的線程調用了UIKit，系統在執行stringByEvaluatingJavaScriptFromString的時候調用了UIKit裏的一些方法，所以不允許在主線程之外的線程去調用這個方法。

解決方法也有很多可以用
[webView performSelectorOnMainThread:]
//或者
dispatch_async(dispatch_get_main_queue(), ^{  
    [webView stringByEvaluatingJavaScriptFromString:@"aaa"];
});        

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