Question

我正在尝试在辅助线程上执行昂贵的操作，我是新手。所以在cellForRowAtIndexPath我使用GCD来设计单元格并将其添加到contentView。

我使用以下方法设计单元格

-(UIView *)designCellAtIndexPath:(NSIndexPath *)indexPath size:(CGSize)aSize
{
    UIView *backView = [[UIView alloc] initWithFrame:CGRectMake(0.0f, 0.0f, aSize.width, aSize.height)];
    ....
    //design the cell with lots of UI elements
    ....
    return backView;
}

我曾在下面试过，但是电池在很长一段时间后（大约8-9秒）正在更新，但是3个日志立即在控制台中打印。

UITableViewCell *cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:nil];
dispatch_queue_t backgroundQueue = dispatch_queue_create("threadToDesignCell", NULL);
    dispatch_async(backgroundQueue, ^{

        NSLog(@"queue interval1- %f", [[NSDate date] timeIntervalSince1970]);
        UIView *cellContentView = [self designCellAtIndexPath:indexPath size:[cell frame].size];
        NSLog(@"queue interval2- %f", [[NSDate date] timeIntervalSince1970]);

        dispatch_async(dispatch_get_main_queue(), ^{

            NSLog(@"queue interval3- %f", [[NSDate date] timeIntervalSince1970]);
            [[cell contentView] addSubview:cellContentView];
            //[cell setNeedsDisplay];
        });
    });

我也曾在下面尝试，但同样的问题就像上面那样出现了。

 dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{

        NSLog(@"queue interval1- %f", [[NSDate date] timeIntervalSince1970]);
        UIView *cellContentView = [self designCellAtIndexPath:indexPath size:[cell frame].size];
        NSLog(@"queue interval2- %f", [[NSDate date] timeIntervalSince1970]);

        dispatch_async(dispatch_get_main_queue(), ^{

            NSLog(@"queue interval3- %f", [[NSDate date] timeIntervalSince1970]);
            [[cell contentView] addSubview:cellContentView];
            //[cell setNeedsDisplay];
        });
    });

在日志中

2015-03-13 12:52:46.515 TableDesigner[2262:65363] queue interval1- 1426231366.515081
2015-03-13 12:52:46.609 TableDesigner[2262:65363] queue interval2- 1426231366.609620
2015-03-13 12:52:46.914 TableDesigner[2262:65326] queue interval3- 1426231366.914309

请帮助我理解这里究竟发生了什么错误。

Answer 1

仅根据标题回答问题：您无法从辅助线程更新UI

我跛行并宣称你的'designCellAtIndexPath'也访问UIKit - 其中99％不是线程安全的，应该只在主线程上完成。：）

所以尝试这个毫无意义的代码，如果你没有遭受巨大的延迟，那就是它

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
    dispatch_async(dispatch_get_main_queue(), ^{
         UIView *cellContentView = [self designCellAtIndexPath:indexPath size:[cell frame].size ];            
         [[cell contentView] addSubview:cellContentView];
    });
});

如何优化此代码以更新UI

1 个答案:

TODO：重写你的designCellAtIndexPath并将其拆分为2种方法。 1用于执行计算，2。用于执行UI相关工作