消息发送到已释放的实例问题

Question

在过去的几个小时里我一直在调试以下问题，但似乎无法得出一个好的结论。

-[NSIndexPath row]：发送到已释放实例 0x506cf90 的消息

我正在 UITableView 上的每个单元格上实现一个滑动识别器。每当检测到滑动时，就会调用下面的代码。它的作用是显示/隐藏单元格中的子视图。如果子视图已经显示，则隐藏，否则显示。如果子视图已显示在单元格 5 上，并且在单元格 3 上检测到滑动，那么我们首先删除该子视图，然后在单元格 3 上添加子视图。

我尝试了下面的代码，它似乎适用于某些单元格。但是，特别是在 UITableView 底部有一个单元格，如果我尝试隐藏子视图，则会出现上述错误。它对于其他单元格（仅是底部的单元格）来说效果非常好。这是为什么呢？

代码如下：

- (void)swipe:(UISwipeGestureRecognizer *)recognizer direction:(UISwipeGestureRecognizerDirection)direction
{
    if (recognizer && recognizer.state == UIGestureRecognizerStateEnded)
    {
        // Get the table view cell where the swipe occured
        CGPoint location = [recognizer locationInView:self.table];
        NSIndexPath* indexPath = [self.table indexPathForRowAtPoint:location];
        ConvoreCell* cell = (ConvoreCell *) [self.table cellForRowAtIndexPath:indexPath];

        [self.table beginUpdates];

        NSLog(@"ROW is %d", global.row);
        //removing the options view at the other cell before adding a new one
        if (global != nil && global.row != indexPath.row){
            [sideSwipeView removeFromSuperview];
            [sideSwipeView release];
            sideSwipeView = nil;
        }

        //options already exist, we need to remove it
        if (sideSwipeView != nil){
            [sideSwipeView removeFromSuperview];
            [sideSwipeView release];
            sideSwipeView = nil;
            slide = NO;
        } else {
            //options do not exist and therefore we need to add it
            NSArray * buttonData = [[NSArray arrayWithObjects:
                                     [NSDictionary dictionaryWithObjectsAndKeys:@"Mark Read", @"title", @"mark.png", @"image", nil],
                                     [NSDictionary dictionaryWithObjectsAndKeys:@"Track", @"title", @"play.png", @"image", nil],
                                     [NSDictionary dictionaryWithObjectsAndKeys:@"Leave", @"title", @"delete.png", @"image", nil],
                                     nil] retain];

            NSMutableArray * buttons = [[NSMutableArray alloc] initWithCapacity:buttonData.count];
            sideSwipeView = [[UIView alloc] initWithFrame:CGRectMake(0, cell.frame.size.height-25, 320, 25)];
            [sideSwipeView setAutoresizingMask:UIViewAutoresizingFlexibleTopMargin];
            [sideSwipeView setBackgroundColor:[UIColor colorWithPatternImage: [UIImage imageNamed:@"dotted-pattern.png"]]];
            [sideSwipeView setTag:-10];

            CGFloat leftEdge = BUTTON_LEFT_MARGIN;
            for (NSDictionary* buttonInfo in buttonData)
            {
                if (!([[buttonInfo objectForKey:@"title"] isEqualToString:@"Mark Read"] && [[[groups objectAtIndex:indexPath.row] unread] intValue] == 0))
                {

                    UIButton* button = [UIButton buttonWithType:UIButtonTypeCustom];

                    button.autoresizingMask = UIViewAutoresizingFlexibleRightMargin | UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleBottomMargin | UIViewAutoresizingFlexibleTopMargin;

                    UIImage* buttonImage = [UIImage imageNamed:[buttonInfo objectForKey:@"image"]];
                    if ([[[groups objectAtIndex:indexPath.row] tracked] intValue] == 1 && [[buttonInfo objectForKey:@"title"] isEqualToString:@"Track"]){
                        buttonImage = [UIImage imageNamed:@"pause.png"];
                        [button setSelected:YES];
                    } else 
                        [button setSelected:NO];

                    button.frame = CGRectMake(leftEdge, 0, buttonImage.size.width, buttonImage.size.height);

                    UIImage* grayImage = [self imageFilledWith:[UIColor colorWithWhite:0.9 alpha:1.0] using:buttonImage];
                    [button setImage:grayImage forState:UIControlStateNormal];

                    if ([[buttonInfo objectForKey:@"title"] isEqualToString:@"Mark Read"]){
                        [button addTarget:self action:@selector(markRead:) forControlEvents:UIControlEventTouchUpInside];
                    } else if ([[buttonInfo objectForKey:@"title"] isEqualToString:@"Track"]){
                        [button addTarget:self action:@selector(track:) forControlEvents:UIControlEventTouchUpInside];
                    } else if ([[buttonInfo objectForKey:@"title"] isEqualToString:@"Leave"]){
                        [button addTarget:self action:@selector(leave:) forControlEvents:UIControlEventTouchUpInside];
                    }
                    [button setTag:indexPath.row];
                    [buttons addObject:button];

                    [sideSwipeView addSubview:button];
                    leftEdge = leftEdge + buttonImage.size.width + BUTTON_SPACING;
                }
            }

            [cell.contentView addSubview:sideSwipeView];
            [buttons release];
            [buttonData release];
            global = indexPath;
            slide = YES;

        }
        [self.table endUpdates]; 
        [self.table deselectRowAtIndexPath:indexPath animated:YES];        

    }
}

现在的问题是指向indexPath 的指针不知何故被释放。我可以通过制作 indexPath 的副本而不是仅仅引用指针来解决这个问题。所以我这样做了：

global = [indexPath copy];

出于某种原因，在调用此方法后，它会释放indexPath，我不确定是谁做的..我认为iOS会这样做...这是真的吗？

Answer 1

    NSIndexPath* indexPath = [self.table indexPathForRowAtPoint:location];

这会返回一个自动释放的实例。所以，是的，您对 global 的分配需要保留该对象。 copy 有效地返回保留的实例。

不过别漏了。如果你这样做：

global = [indexPath copy];

并且你不首先释放 global 的原始值，你就会泄漏。

哦，还有：http://developer.apple。 com/library/mac/#documentation/Cocoa/Conceptual/MemoryMgmt/MemoryMgmt.html