ios - 试图了解 cellForRowAtIndexPath 和 heightForRowAtIndexPath 在处理 UITableViewCells 时如何工作

Question

在StackOverflow好心人的帮助下，我有这两个方法:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{    
    UITableViewCell *cell = [[UITableViewCell alloc] initWithStyle:(UITableViewCellStyleDefault)
            reuseIdentifier:@"business"];

    NSString *comment = [[items_array objectAtIndex:[indexPath row]] objectForKey:(@"comment")];

    NSLog(businessPrivacy);
    // FIND IF THE BUSINESS PLAN IS PRIVATE OR NOT.

        CGSize constraint = CGSizeMake(320 - (10 * 2), 20000.0f); 

        CGSize size = [comment sizeWithFont:[UIFont systemFontOfSize:14] constrainedToSize:constraint lineBreakMode:UILineBreakModeWordWrap]; 

        UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 300, MAX(size.height, 44.0f) + 20.0f)]; 
        label.numberOfLines = 0; 
        label.lineBreakMode = UILineBreakModeWordWrap; 
        label.text = comment;  

        [cell.contentView addSubview:label];        

    return cell;
}

//Cell size for word wrapping.
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath;
{    
    NSString *comment = [[items_array objectAtIndex:[indexPath row]] objectForKey:(@"comment")];

    CGSize constraint = CGSizeMake(320 - (10 * 2), 20000.0f); 

    CGSize size = [comment sizeWithFont:[UIFont systemFontOfSize:14] constrainedToSize:constraint lineBreakMode:UILineBreakModeWordWrap]; 

    CGFloat height = MAX(size.height, 44.0f);

    return height + (10 * 2);
}

它们的效果是从默认字体大小减小字体大小，并动态调整大小以几乎适合评论的整个文本，无论该文本可能有多长。

令我感到困惑的是，我在这两种方法中都有一些相同的代码，而且我不知道它到底应该是什么样子。我确实知道这两种方法都被调用了，但不确定应该在哪里调用它们才能正常工作。

提前感谢您的建议。

Answer 1

看起来您两者都需要它们。我已经用注释重写了您的代码，以便您可以理解它:

//This function is used to create the cell and the content of the cell.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{   
    //Here you are allocating a new cell with a reuse identifier.  This is only needed if
    //you plan on reusing the cells and using [tableView dequeueReusableCellWithIdentifier:cellIdentifier]
    //Reusable cells will save you some memory and make your tableview work more smoothly,
    //however here you are not selecting from the reusable pool, and are instead making a new cell each time
    UITableViewCell *cell = [[UITableViewCell alloc] initWithStyle:(UITableViewCellStyleDefault)
            reuseIdentifier:@"business"];

    //This is pulling the text for the comment, it is obviously necessary
    NSString *comment = [[items_array objectAtIndex:[indexPath row]] objectForKey:(@"comment")];

    NSLog(businessPrivacy);
    // FIND IF THE BUSINESS PLAN IS PRIVATE OR NOT.

    // This is creating a constraint size for the label you are making
    CGSize constraint = CGSizeMake(320 - (10 * 2), 20000.0f); 

    // This is determining the size that you will need for the label based on the comment
    // length and the contraint size
    CGSize size = [comment sizeWithFont:[UIFont systemFontOfSize:14] constrainedToSize:constraint lineBreakMode:UILineBreakModeWordWrap]; 

    //  Here you are creating your label and initializing it with the frame that you have
    //  determined by your size calculations above
    UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 300, MAX(size.height, 44.0f) + 20.0f)];

    // setting up the label properties
    label.numberOfLines = 0;
    label.lineBreakMode = UILineBreakModeWordWrap; 
    label.text = comment;  

    // adding the label view to the cell that you have created
    [cell.contentView addSubview:label];        

    // return the cell for the table view
    return cell;
}

//Cell size for word wrapping.
//This method will determine how tall each row needs to be.
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath;
{
    //Here you are getting the comment again.  This is necessary to determine how tall you need
    //the cell to be    
    NSString *comment = [[items_array objectAtIndex:[indexPath row]] objectForKey:(@"comment")];

    // Again you are getting the constraints because you are going to us this size
    // to constrain the height of the cell just like you determined the size for the label.
    CGSize constraint = CGSizeMake(320 - (10 * 2), 20000.0f); 

    // Again, determining the size that we will need for the label, because it will drive
    // the height of the cell
    CGSize size = [comment sizeWithFont:[UIFont systemFontOfSize:14] constrainedToSize:constraint lineBreakMode:UILineBreakModeWordWrap]; 

    //  Finally, we can determine the height for the cell!
    CGFloat height = MAX(size.height, 44.0f);

    //  return the height, which is the height of the label plus some extra space to make
    //  it look good.
    return height + (10 * 2);
}

基本上，cellForRow... 函数创建单元格的内容，heightForRow... 函数确定高度。您需要它们中的所有信息，因为 cell 函数仅创建单元格的内容，而 height 函数创建行的高度和注释、约束和大小对于确定单元格内容的 label 大小和单元格高度都很重要。