重用细胞...... :( [英] Reuse cell... :(

问题描述

我有一个包含9个部分和56行的表格。

I have a table with 9 sections and 56 rows.

我想为每个单元格添加文本标签。我用56 NSDictionaries 和一个数组创建了一个 NSArray menuList 包含每个部分中的行数（ sectionsArray ）。

I want to add a text label for each cell. I created a NSArray menuList with 56 NSDictionaries and an array containing the number of rows in each section (sectionsArray).

这是我的代码，但它没有完全正常工作：

Here is my code, but it doesn't work properly at all:

// Customize the appearance of table view cells.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

    //Use existing cell (reusable)
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:kCellIdentifier];

    //If no existing cell, create a new one
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:kCellIdentifier] autorelease];

        //Define cell accessory type
        cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;

        //Create a subView for the cell
        CGRect subViewFrame = cell.contentView.frame;
        subViewFrame.origin.x += kInset;
        subViewFrame.size.width = kInset + kSelectLabelWidth;

        UILabel *selectedLabel = [[UILabel alloc] initWithFrame:subViewFrame];

        //SubView design
        selectedLabel.textColor = [UIColor blackColor];
        selectedLabel.highlightedTextColor = [UIColor whiteColor];
        selectedLabel.backgroundColor = [UIColor clearColor];

        [cell.contentView addSubview:selectedLabel];

        int indRow = 0;
        for (int i =0; i < indexPath.section; i++) {
            indRow += [[sectionsArray objectAtIndex:i] intValue];
        }
        indRow += indexPath.row;

        NSDictionary *cellText = [menuList objectAtIndex:indRow];

        selectedLabel.text = [cellText objectForKey:@"selection"];
        [selectedLabel release];

    }
    return cell;        
}

此代码有什么问题？

在 iOSSimulator 中，我看到当我滚动时，单元格的文本有时发生变化，标签的顺序不正确。

In iOSSimulator, i see that cell's text change sometimes when I'm scrolling, and labels are not in the right order.

推荐答案

填写您单元格的所有代码都在：

All the code that fills in your cells is with in the:

if (cell == nil) {

语句，所以你最终创建了一个少量细胞并将它们填入（当细胞== nil时），然后只返回出列的细胞。

statement, so you end up creating a small number of cells and filling them in (when cell==nil) and then just return the dequeued ones.

这应该是：

// Customize the appearance of table view cells.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

    //Use existing cell (reusable)
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:kCellIdentifier];

    //If no existing cell, create a new one
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:kCellIdentifier] autorelease];

        //Define cell accessory type
        cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;

        //Create a subView for the cell
        CGRect subViewFrame = cell.contentView.frame;
        subViewFrame.origin.x += kInset;
        subViewFrame.size.width = kInset + kSelectLabelWidth;

        UILabel *selectedLabel = [[UILabel alloc] initWithFrame:subViewFrame];

        //SubView design
        selectedLabel.textColor = [UIColor blackColor];
        selectedLabel.highlightedTextColor = [UIColor whiteColor];
        selectedLabel.backgroundColor = [UIColor clearColor];

        [cell.contentView addSubview:selectedLabel];
    }
    // At this point cell whether it is a reused cell or a new one
    // cell points to the object we need to fill in.

    int indRow = 0;
    for (int i =0; i < indexPath.section; i++) {
        indRow += [[sectionsArray objectAtIndex:i] intValue];
    }
    indRow += indexPath.row;

    NSDictionary *cellText = [menuList objectAtIndex:indRow];

    selectedLabel.text = [cellText objectForKey:@"selection"];
    [selectedLabel release];

    return cell;       
}

这是代码正在做的事情：

This is what the code is doing:

Try to get a reusable cell

If no reusable cell is available
{
    create a new cell
}

Fill in the values for the cell

因此，当一个单元格滚动屏幕时，它会被放入进入重用队列。当一个单元格即将进入屏幕时，将调用 cellForRowAtIndexPath 。分配新单元格比重用现有单元格要慢，因此首先尝试从重用队列中获取单元格，但如果没有可用，则创建一个新单元格。然后你填写你的价值观。

So when a cell scrolls of the screen it is put into a reuse queue. When a cell is about to come onto the screen your cellForRowAtIndexPath is called. Allocating a new cell is slower than reusing an existing one, so you first try to get a cell from the reuse queue, but if one is not available you create a new one. Then you fill in your values.

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