异步加载UIViews

Question

我正在尝试异步加载视图。问题是要加载的视图框架依赖于异步加载的数据。换句话说，有一些很长的计算来决定在哪里实际显示UIViews。

我知道在线程中实际显示UIView时会出现问题，您应该始终将它们重新加载到主线程中，所以这是我一直在尝试的代码：

asyncQueue = [[NSOperationQueue alloc] init];
[asyncQueue addOperationWithBlock:^{
    // Do work to load the UIViews and figure out where they should be
    UIButton *test = [[UIButton alloc] initWithFrame:[self doWorkToGetFrame]];

    [[NSOperationQueue mainQueue] addOperationWithBlock:^{
            [self addSubview:test];
        }
    }];
}];

这些都驻留在一个UIView容器中。

Answer 1

尝试如下所示：

UIButton *test = [[UIButton alloc] initWithFrame:CGRectZero];
test.hidden = YES;
test.alpha = 0.0f;
[self addSubview:test];

dispatch_queue_t downloadQueue = dispatch_queue_create("myDownloadQueue",NULL);
dispatch_async(downloadQueue, ^
{
  // do work to load UIViews and calculate frame
  CGRect frameButton = ...;

  dispatch_async(dispatch_get_main_queue(), ^
  {
    test.hidden = NO; 
    [UIView animateWithDuration:0.4f animations:^
    {
     test.frame = frameButton;
     test.alpha = 1.0f;
    } 
    completion:^(BOOL finished){}];


  });
});

dispatch_release(downloadQueue);

这会将您的按钮添加到主线程中，但最初会使其不可见。背景工作完成后，您将使其可见，并使用动画设置帧。