尝试通过 viewWithTag 获取 UIImageView 引用后崩溃
我需要在表格单元格中绘制图像。到目前为止，在创建视图并将其分配给单元格后，我无法获得对 UIImageView 的正确引用。例如，相同的过程适用于 UILabel。
我不明白我做错了什么。
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = @"Cell";
UIImageView *imageView;
UILabel *title;
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault
reuseIdentifier:CellIdentifier] autorelease];
// Setup title
title = [[[UILabel alloc] initWithFrame:CGRectMake(0, 0, 100, 30)] autorelease];
title.tag = 1;
[cell.contentView addSubview:title];
// Setup image
UIImageView* imageView = [[[ UIImageView alloc] initWithFrame:
CGRectMake(50, 0, 50, 50)] autorelease];
imageView.tag = 2;
[cell.contentView addSubview:imageView];
} else {
// Get references to cell views
title = (UILabel *)[cell.contentView viewWithTag:1];
imageView = (UIImageView *)[cell.contentView viewWithTag:2];
}
NSLog(@"%@", [title class]); // UILabel
NSLog(@"%@", [imageView class]); // CRASH! EXC_BAD_ACCESS
return cell;
}
I need to draw an image in a table cell. So far I have not been able to get a proper reference to the UIImageView after I create the view and assign it to the cell. The same procedure does work for a UILabel, for example.
I can't figure out what I'm doing wrong.
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = @"Cell";
UIImageView *imageView;
UILabel *title;
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault
reuseIdentifier:CellIdentifier] autorelease];
// Setup title
title = [[[UILabel alloc] initWithFrame:CGRectMake(0, 0, 100, 30)] autorelease];
title.tag = 1;
[cell.contentView addSubview:title];
// Setup image
UIImageView* imageView = [[[ UIImageView alloc] initWithFrame:
CGRectMake(50, 0, 50, 50)] autorelease];
imageView.tag = 2;
[cell.contentView addSubview:imageView];
} else {
// Get references to cell views
title = (UILabel *)[cell.contentView viewWithTag:1];
imageView = (UIImageView *)[cell.contentView viewWithTag:2];
}
NSLog(@"%@", [title class]); // UILabel
NSLog(@"%@", [imageView class]); // CRASH! EXC_BAD_ACCESS
return cell;
}
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问题在于 imageView 变量的范围。如果单元格尚不存在，您将创建一个仅存在于 if 块中的新
UIImageView。它隐藏了您之前声明的变量，并在 if 块结束后消失。相反，
您应该简单地编写
否则，您将创建一个与您在方法顶部声明的对象无关的新对象，并且原始
imageView仍然未定义。The problem is the scope of the
imageViewvariables. In the case that the cell doesn't exist yet, you create a newUIImageViewthat only exists in the if-block. It hides the variable that you declared earlier and disappears after the if-block ends.Instead of
you should simply write
Otherwise you're creating a new object that has nothing to do with the object you declared at the top of the method and the original
imageViewis still undefined.