在iOS中只有主线程才能立即刷新UI。如果是通过侦听异步消息,触发回调函数,或者调用异步方法,请求刷新UI,都会产生线程阻塞和延迟的问题。
正确的做法是回到主线程,方法如下:
if ([NSThread isMainThread])
{
[self.downloadMapBtn setImage:[UIImage imageNamed:@"download_map.png"] forState:UIControlStateNormal];
[self.downloadMapBtn setNeedsDisplay];
}
else
{
dispatch_sync(dispatch_get_main_queue(), ^{
//Update UI in UI thread here
[self.downloadMapBtn setImage:[UIImage imageNamed:@"download_map.png"] forState:UIControlStateNormal];
[self.downloadMapBtn setNeedsDisplay];
});
}