如何为循环添加延迟? [英] How to add a delay to a loop?

问题描述

我正在尝试使用此代码将图像视图添加到 UIView:

Im attempting add image views to a UIView using this code:

for (int i = 0; i <numberOfImages; i++) {
    UIImageView *image = [UIImageView alloc]initWithFrame:CGRectMake(40, 40, 40, 40)];
    image.image = [images objectAtIndex:i];
    [self.view addSubview:image];
}

这可行，但问题是我希望在添加每个图像之前有 5 秒的延迟，而不是同时添加它们.有人可以帮帮我吗?谢谢.

This works but the problem is I would like to have a 5 second delay before it adds each image, instead it adds them all at the same time. Can anybody help me out? Thanks.

例子:

5 seconds = one image on screen
10 seconds = two images on screen
15 seconds = three images on screen

推荐答案

使用 NSTimer.

NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:numberOfSeconds
                                                      target:self 
                                                    selector:@selector(methodToAddImages:) 
                                                    userInfo:nil 
                                                     repeats:YES];

这实际上会以指定的时间间隔重复调用 methodToAddImages.要停止调用此方法，请调用 [NSTimer invalidate](请记住，无效的计时器无法重复使用，并且您需要创建一个新的计时器对象以防重复此过程).

This will essentially call methodToAddImages repeatedly with the specified time interval. To stop this method from being called, call [NSTimer invalidate] (bear in mind that an invalidated timer cannot be reused, and you will need to create a new timer object in case you want to repeat this process).

在 methodToAddImages 中，您应该有代码来遍历数组并添加图像.您可以使用计数器变量来跟踪索引.

Inside methodToAddImages you should have code to go over the array and add the images. You can use a counter variable to track the index.

另一种选择(我的建议)是拥有此数组的可变副本并将 lastObject 添加为子视图，然后将其从数组的可变副本中删除.

Another option (my recommendation) is to have a mutable copy of this array and add lastObject as a subview and then remove it from the mutable copy of your array.

您可以先按相反的顺序创建一个 mutableCopy，如下所示:

You can do this by first making a mutableCopy in reversed order as shown:

NSMutableArray* reversedImages = [[[images reverseObjectEnumerator] allObjects] mutableCopy];

你的 methodToAddImages 看起来像:

Your methodToAddImages looks like:

- (void)methodToAddImages
{
    if([reversedImages lastObject] == nil)
    {
        [timer invalidate];
        return;
    }

    UIImageView *imageView = [[UIImageView alloc] initWithFrame:(CGRectMake(40, 40, 40, 40))];
    imageView.image = [reversedImages lastObject];
    [self.view addSubview:imageView];
    [reversedImages removeObject:[reversedImages lastObject]];
}

我不知道您使用的是 ARC 还是 Manual Retain Release，但这个答案是假设 ARC 编写的(基于您问题中的代码).

I don't know if you're using ARC or Manual Retain Release, but this answer is written assuming ARC (based on the code in your question).

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