EXC_BAD_ACCESS 在 heightForRowAtIndexPath iOS [英] EXC_BAD_ACCESS in heightForRowAtIndexPath iOS

问题描述

我正在开发一个应用程序，其中有一个 UITableViewCell 的自定义子类.我想根据其中的文本使单元格的高度动态化.我尝试在我的 heightForRowAtIndexPath 方法中做到这一点.但是我遇到了一些问题，以下代码导致和 EXC_BAD_ACCESS(code=2 address=0xb7ffffcc) 错误.

I'm working on an application where I have a custom subclass of UITableViewCell. I want to make the cell's height dynamic based on the text inside it. I try do do that in my heightForRowAtIndexPath method. But I'm having some issues, the following code causes and EXC_BAD_ACCESS(code=2 address=0xb7ffffcc) error.

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{

    PostCell *cell = (PostCell *)[tableView cellForRowAtIndexPath:indexPath];

    CGSize postTextSize;
    if (![cell.postText.text isEqualToString:@""]) {
        postTextSize = [cell.postText.text sizeWithFont:[UIFont systemFontOfSize:14] constrainedToSize:CGSizeMake(cell.postText.frame.size.width, 200)];
    } else {
        postTextSize = CGSizeMake(cell.postText.frame.size.width, 40);
    }

    return postTextSize.height + cell.userName.frame.size.height + 10;
}

如果我改为:

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{   
    return 100;
}

它有效.

似乎在这一行崩溃了:PostCell *cell = (PostCell *)[tableView cellForRowAtIndexPath:indexPath];，我不知道为什么.我试图建立干净并重置模拟器，但都没有奏效.任何想法为什么会发生这种情况?

It seems to be crashing on this line: PostCell *cell = (PostCell *)[tableView cellForRowAtIndexPath:indexPath];, and I don't know why. I have tried to build clean and reset the simulator, but neither worked. Any ideas why this is happening?

推荐答案

我已尝试重现该问题.事实证明，在 heightForRowAtIndexPath 中调用 cellForRowAtIndexPath: 会导致 heightForRowAtIndexPath 被递归调用.这是 3 个递归步骤后堆栈回溯的摘录:

I have tried to reproduce the problem. It turns out that calling cellForRowAtIndexPath: inside heightForRowAtIndexPath causes heightForRowAtIndexPath to be called recursively. Here is an extract of the stack backtrace after the 3 recursion steps:

frame #0: 0x000042d0 DocInteraction`-[DITableViewController tableView:heightForRowAtIndexPath:] + 48 at DITableViewController.m:262
frame #1: 0x0054f688 UIKit`-[UISectionRowData refreshWithSection:tableView:tableViewRowData:] + 3437
frame #2: 0x0055040f UIKit`-[UITableViewRowData(UITableViewRowDataPrivate) _ensureSectionOffsetIsValidForSection:] + 144
frame #3: 0x00551889 UIKit`-[UITableViewRowData numberOfRows] + 137
frame #4: 0x00553dac UIKit`-[UITableViewRowData globalRowsInRect:] + 42
frame #5: 0x003f82eb UIKit`-[UITableView(_UITableViewPrivate) _visibleGlobalRowsInRect:] + 177
frame #6: 0x004001e6 UIKit`-[UITableView cellForRowAtIndexPath:] + 113
frame #7: 0x000042f2 DocInteraction`-[DITableViewController tableView:heightForRowAtIndexPath:] + 82 at DITableViewController.m:262
frame #8: 0x0054f688 UIKit`-[UISectionRowData refreshWithSection:tableView:tableViewRowData:] + 3437
frame #9: 0x0055040f UIKit`-[UITableViewRowData(UITableViewRowDataPrivate) _ensureSectionOffsetIsValidForSection:] + 144
frame #10: 0x00551889 UIKit`-[UITableViewRowData numberOfRows] + 137
frame #11: 0x00553dac UIKit`-[UITableViewRowData globalRowsInRect:] + 42
frame #12: 0x003f82eb UIKit`-[UITableView(_UITableViewPrivate) _visibleGlobalRowsInRect:] + 177
frame #13: 0x004001e6 UIKit`-[UITableView cellForRowAtIndexPath:] + 113
frame #14: 0x000042f2 DocInteraction`-[DITableViewController tableView:heightForRowAtIndexPath:] + 82 at DITableViewController.m:262
frame #15: 0x0054f688 UIKit`-[UISectionRowData refreshWithSection:tableView:tableViewRowData:] + 3437
frame #16: 0x0055040f UIKit`-[UITableViewRowData(UITableViewRowDataPrivate) _ensureSectionOffsetIsValidForSection:] + 144
frame #17: 0x00551889 UIKit`-[UITableViewRowData numberOfRows] + 137
frame #18: 0x003ff66d UIKit`-[UITableView noteNumberOfRowsChanged] + 119
frame #19: 0x003ff167 UIKit`-[UITableView reloadData] + 764

最后程序崩溃了.在我的模拟器上，当回溯深度大约为 57000 级时，就会发生这种情况.

Finally the program crashes. On my Simulator this happens when the back trace is about 57000 levels deep.

旧答案(没有错，但没有解释EXC_BAD_ACCESS):

Old answer (not wrong, but does not explain the EXC_BAD_ACCESS):

问题在于

[tableView cellForRowAtIndexPath:indexPath]

对于当前不可见的行返回 nil.表视图仅分配显示当前可见行所需的单元格.滚动表格视图时会重复使用单元格.

returns nil for rows that are currently not visible. A table view allocates only so many cells that are required to display the currently visible rows. The cells are reused when you scroll the table view.

但是 heightForRowAtIndexPath 在显示任何行之前为表格视图的所有单元格调用.

But heightForRowAtIndexPath is called for all cells of the table view before any row is displayed.

因此，您不应从表格视图单元格中获取文本来计算 heightForRowAtIndexPath 中的高度.您应该改为从数据源获取文本.

As a consequence, you should not get the text from the table view cells to compute the height in heightForRowAtIndexPath. You should get the text from your data source instead.

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