一、问题描述
-(void)sendAsynchronousRequest
{
NSLog(@"%@",[NSThread currentThread]);
[SVProgressHUD showWithStatus:@"正在登录....." maskType:SVProgressHUDMaskTypeBlack];
NSString *urlString = [NSString stringWithFormat:@"http://120.25.226.186:32812/login?username=%@&pwd=%@&type=JSON",self.userName.text,self.userPWD.text];
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:urlString]];
NSOperationQueue *operationQueue = [[NSOperationQueue alloc]init];
[NSURLConnection sendAsynchronousRequest:request queue:operationQueue completionHandler:^(NSURLResponse * _Nullable response, NSData * _Nullable data, NSError * _Nullable connectionError) {
NSString *jsonString = [[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding];
NSRange rangeStart = [jsonString rangeOfString:@"\":\""];
NSUInteger start = rangeStart.location+;
NSRange rangeEnd = [jsonString rangeOfString:@"\"}"];
NSUInteger end = rangeEnd.location;
NSUInteger length = end-start;
NSString *message =[jsonString substringWithRange:NSMakeRange(start, length)];
if([jsonString containsString:@"success"])
{
NSLog(@"%@",[NSThread currentThread]);
[SVProgressHUD showSuccessWithStatus:message maskType:SVProgressHUDMaskTypeBlack];
}
else
{
NSLog(@"%@",[NSThread currentThread]);
[SVProgressHUD showSuccessWithStatus:message maskType:SVProgressHUDMaskTypeBlack];
}
}];
}
运行时发生以下警告:
This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes. This will cause an exception in a future release.
二、问题分析
此应用程序是由一个后台线程修改布局，从而导致崩溃，将导致在未来的版本异常。
更新UI必须在主线程。调用NSURLConnection的sendAsynchronousRequest: queue: completionHandler:方法会创建子线程执行请求，而在Block回调中调用的是主线程SVProgressHUD对象，从而导致错误。通过[NSThread currentThread]打印前后线程，前者在主线程：<NSThread: 0x7fbac9c074e0>{number = 1, name = main}，后者在子线程<NSThread: 0x7fbacc0208a0>{number = 3, name = (null)}。
三、问题解决
例如：GCD代码
dispatch_async(dispatch_get_main_queue(), ^{
// 更UI
});
修改如下：
-(void)sendAsynchronousRequest
{
NSLog(@"%@",[NSThread currentThread]);
[SVProgressHUD showWithStatus:@"正在登录....." maskType:SVProgressHUDMaskTypeBlack];
NSString *urlString = [NSString stringWithFormat:@"http://120.25.226.186:32812/login?username=%@&pwd=%@&type=JSON",self.userName.text,self.userPWD.text];
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:urlString]];
NSOperationQueue *operationQueue = [[NSOperationQueue alloc]init]; [NSURLConnection sendAsynchronousRequest:request queue:operationQueue completionHandler:^(NSURLResponse * _Nullable response, NSData * _Nullable data, NSError * _Nullable connectionError) {
NSString *jsonString = [[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding];
NSRange rangeStart = [jsonString rangeOfString:@"\":\""];
NSUInteger start = rangeStart.location+;
NSRange rangeEnd = [jsonString rangeOfString:@"\"}"];
NSUInteger end = rangeEnd.location;
NSUInteger length = end-start;
NSString *message =[jsonString substringWithRange:NSMakeRange(start, length)];
if([jsonString containsString:@"success"])
{
NSLog(@"%@",[NSThread currentThread]);
dispatch_async(dispatch_get_main_queue(), ^{
[SVProgressHUD showSuccessWithStatus:message maskType:SVProgressHUDMaskTypeBlack];
});
}
else
{
NSLog(@"%@",[NSThread currentThread]);
dispatch_async(dispatch_get_main_queue(), ^{
[SVProgressHUD showSuccessWithStatus:message maskType:SVProgressHUDMaskTypeBlack];
});
}
}];
}