Question

我必须填充行数。当我使用

UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

这一行，在滚动到某些行后，它会在同一位置重绘行。请在屏幕下方查看 enter image description here

如果我使单元格为零，即

UITableViewCell *cell = nil;

然后工作正常，但它需要更多的记忆。现在我的问题是它为什么会发生。

将单元格nil重绘在相同位置的关系是什么？

这是我的代码：

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
    }

    UIButton *questionButton=[UIButton buttonWithType:UIButtonTypeCustom];
    questionButton.backgroundColor=[UIColor clearColor];
    questionButton.tag=indexPath.row+1;

    [questionButton setContentHorizontalAlignment:UIControlContentHorizontalAlignmentLeft];

    UIImageView *statusImageView=[[UIImageView alloc]initWithFrame:CGRectMake(190,25,23,23)];

    NSString *statusImageName=[[NSString  alloc]init];
    statusImageName=@"Right";
    [statusImageView setImage:[UIImage imageNamed:statusImageName]];
    [questionButton addSubview:statusImageView];

    if(indexPath.row%2==0)
    {
        [questionButton setBackgroundImage:[UIImage imageNamed:@"TopicsbarLeft"] forState:UIControlStateNormal];
        [questionButton setBackgroundImage:[UIImage imageNamed:@"TopicsbarLetSelected"] forState:UIControlStateHighlighted];
        CGRect topicButtonFrame=CGRectMake(0, 10, 250, 70);
        questionButton.frame=topicButtonFrame;



        NSLog(@"Even Rows =%d",indexPath.row);

        NSString *questionLabel=[NSString stringWithFormat:@" Question %d :",indexPath.row+1];
        [questionButton setTitle:questionLabel forState:UIControlStateNormal];
        //questionButton.titleLabel.textAlignment=NSTextAlignmentLeft;

        [questionButton.titleLabel setTextAlignment:UITextAlignmentLeft];
    }
    else
    {
        [questionButton setBackgroundImage:[UIImage imageNamed:@"TopicsbarRight"] forState:UIControlStateNormal];
        [questionButton setBackgroundImage:[UIImage imageNamed:@"TopicsbarRightSelected"] forState:UIControlStateHighlighted];
        CGRect topicButtonFrame=CGRectMake(100, 10, 250, 70);
        questionButton.frame=topicButtonFrame;


        NSString *questionLabel=[NSString stringWithFormat:@"     Question %d :",indexPath.row+1];
        [questionButton setTitle:questionLabel forState:UIControlStateNormal];
        questionButton.titleLabel.textAlignment=UITextAlignmentRight;
        [cell addSubview:questionButton];

    }

    [cell addSubview:questionButton];

    cell.selectionStyle=UITableViewCellSelectionStyleNone;
    return cell;
}

Answer 1

dequeueReusableCellWithIdentifier的目的是减少使用内存。如果屏幕可以容纳4或5个表格单元格，那么重复使用时，即使表格有1000个条目，也只需要在内存中分配4或5个表格单元格。

因此，当您执行此操作UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];时，它会返回旧单元格以供重用。它不是一个新的单元格实例。它包含初始化为旧数据的单元格的UI元素。要再次显示它，您需要重置所有UI元素并输入新值。

放置UITableViewCell *cell = nil;时的第二种方法是不重用。第二种方式没有优势，只使用一组表格单元格。如果您的表有1000个条目，那么您将在内存中分配1000个单元格。如果你打算这样做，你会把它们放在一个数组中，然后用行号索引数组并返回单元格。这应该可以解释你的内存使用量的高峰，因为它没有重用任何单元实例。

对于具有固定单元的小型表，第二种解决方案可能是一种合理的解决方案，对于动态或大型表，重用是最好的方法...

更新：，因为您要求提供一些代码。另请注意，根据奇数或偶数，您正在进行两种类型的渲染。因此，当您想显示偶数编号的问题时，来自reuse的单元格可能会很奇怪。在这种情况下，您需要在获取单元格之后重置单元格（从重用或创建新单元格）并让您的正常逻辑流过......

    [questionButton setBackgroundImage:[UIImage imageNamed:@"default.png"]];
    [questionButton setTitle:@"" forState:UIControlStateNormal];
    CGRect topicButtonFrame=CGRectMake(0, 0, 250, 70);
    questionButton.frame=topicButtonFrame;

Answer 2

问题在于：

        [cell addSubview:questionButton];
    }
    [cell addSubview:questionButton];

您要添加两次问题按钮。请删除其他部分，然后尝试。

更新：

你可以试试这个只是为了确认问题是什么：

if(indexPath.row%2==0)
{
    UIButton *questionButton=[UIButton buttonWithType:UIButtonTypeCustom];
    questionButton.backgroundColor=[UIColor clearColor];
    questionButton.tag=indexPath.row+1;

    [questionButton setContentHorizontalAlignment:UIControlContentHorizontalAlignmentLeft];

    UIImageView *statusImageView=[[UIImageView alloc]initWithFrame:CGRectMake(190,25,23,23)];

    NSString *statusImageName=[[NSString  alloc]init];
    statusImageName=@"Right";
    [statusImageView setImage:[UIImage imageNamed:statusImageName]];
    [questionButton addSubview:statusImageView];
    [questionButton setBackgroundImage:[UIImage imageNamed:@"TopicsbarLeft"] forState:UIControlStateNormal];
    [questionButton setBackgroundImage:[UIImage imageNamed:@"TopicsbarLetSelected"] forState:UIControlStateHighlighted];
    CGRect topicButtonFrame=CGRectMake(0, 10, 250, 70);
    questionButton.frame=topicButtonFrame;

    NSString *questionLabel=[NSString stringWithFormat:@" Question %d :",indexPath.row+1];
    [questionButton setTitle:questionLabel forState:UIControlStateNormal];
    //questionButton.titleLabel.textAlignment=NSTextAlignmentLeft;

    [questionButton.titleLabel setTextAlignment:UITextAlignmentLeft];
    [cell addSubview:questionButton];
}
else
{
    UIButton *questionButton=[UIButton buttonWithType:UIButtonTypeCustom];
    questionButton.backgroundColor=[UIColor clearColor];
    questionButton.tag=indexPath.row+1;

    [questionButton setContentHorizontalAlignment:UIControlContentHorizontalAlignmentLeft];

    UIImageView *statusImageView=[[UIImageView alloc]initWithFrame:CGRectMake(190,25,23,23)];

    NSString *statusImageName=[[NSString  alloc]init];
    statusImageName=@"Right";
    [statusImageView setImage:[UIImage imageNamed:statusImageName]];
    [questionButton addSubview:statusImageView];
    [questionButton setBackgroundImage:[UIImage imageNamed:@"TopicsbarRight"] forState:UIControlStateNormal];
    [questionButton setBackgroundImage:[UIImage imageNamed:@"TopicsbarRightSelected"] forState:UIControlStateHighlighted];
    CGRect topicButtonFrame=CGRectMake(100, 10, 250, 70);
    questionButton.frame=topicButtonFrame;


    NSString *questionLabel=[NSString stringWithFormat:@"     Question %d :",indexPath.row+1];
    [questionButton setTitle:questionLabel forState:UIControlStateNormal];
    questionButton.titleLabel.textAlignment=UITextAlignmentRight;
    [cell addSubview:questionButton];

}

表格单元格绘制在同一位置

2 个答案: