Question

我有一个for循环设置按钮上的背景图像，基本上按钮是不同项目的缩略图预览＆amp;不能静态设置，但代码会发出警告，因为它遍历所有UIViews，但随后调用setBackgroundImage，它不适用于所有视图。警告是一种刺激，我理解它在抱怨什么，我怎么能摆脱它？（我不想关闭警告，我想解决问题）

// For loop to set button images  
for (UIView *subview in [self.view subviews])  // Loop through all subviews  
{  
  // Look for the tagged buttons, only the 8 tagged buttons & within array bounds
  if((subview.tag >= 1) && (subview.tag <= 8) && (subview.tag < totalBundles))
  {
    // Retrieve item in array at position matching button tag (array is 0 indexed)
    NSDictionary *bundlesDataItem = [bundlesDataSource objectAtIndex:(subview.tag - 1)];

    // Set button background to thumbnail of current bundle
    NSString *picAddress = [NSString stringWithFormat:@"http://some.thing.com/data/images/%@/%@", [bundlesDataItem objectForKey:@"Nr"], [bundlesDataItem objectForKey:@"Thumb"]];
    NSURL *picURL = [NSURL URLWithString:picAddress];
    NSData *picData = [NSData dataWithContentsOfURL:picURL];
    // Warning is generated here
    [subview setBackgroundImage:[UIImage imageWithData:picData] forState:UIControlStateNormal];
  }
}

Answer 1

你可以这样做：

for (id subview in [self.view subviews])

这样id类型将停止任何类型检查...或者检查对象是否响应选择器并像这样调用它：

if ([subview respondsToSelector:@selector(setBackgroundImage:forState:)]) {
    [subview performSelector:@selector(setBackgroundImage:forState:)
                  withObject:[UIImage imageWithData:picData]
                  withObject:UIControlStateNormal];
}

请注意，我在内存中编写了最后一部分。

Answer 2

具有如此多假设的危险代码，但是......在发送一个setBackgroundImage消息之前，你首先要检查UIView的类，然后只需简单地转换你的UIView来删除警告：

if ([subview class] == [UIButton class]) {
    [((UIButton *)subview) setBackgroundImage:[UIImage imageWithData:picData] forState:UIControlStateNormal];
}

由UIButton设置代码生成的警告

2 个答案: