iOS中的EXC_BAD_ACCESS为heightForRowAtIndexPath [英] EXC_BAD_ACCESS in heightForRowAtIndexPath iOS

问题描述

我正在开发一个应用程序，我有一个UITableViewCell的自定义子类。我想根据里面的文字使单元格的高度动态变化。我尝试在我的heightForRowAtIndexPath方法中这样做。但我有一些问题，以下代码导致和EXC_BAD_ACCESS（代码= 2地址= 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。

这一行似乎崩溃了： 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，但都没有工作。任何想法为什么会这样？

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

我试图重现这个问题。事实证明，在 heightForRowAtIndexPath 内调用 cellForRowAtIndexPath：会导致 heightForRowAtIndexPath 被递归地调用。以下是3个递归步骤之后的堆栈回溯的摘录：

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，这种情况发生在后跟踪深度约为57000级时。

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

旧答案 （没错，但不解释
EXC_BAD_ACCESS）：

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

问题是

[tableView cellForRowAtIndexPath:indexPath]

返回 nil 表示当前不可见的行。表视图仅分配显示当前可见行所需的许多单元格。滚动表格视图时会重复使用这些单元格。

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 all heightForRowAtIndexPath em>在显示任何行之前的表视图的单元格。

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

因此，您不应该从表格视图单元格中获取文本以计算<$中的高度C $ C> heightForRowAtIndexPath 。您应该从数据源获取文本。

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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