ios - 什么时候释放 UITableView 单元格中的 UIButton？

Question

我试图在我的 cellForRowAtIndexPath 方法中向单元格添加一个按钮。这行得通，但我似乎在每次更新单元格时都添加了一个按钮(发现这一点是因为我更新了错误的屏幕位置，并且我有 2 个既可以工作又可以点击的按钮)。

分配和释放添加到单元格的 UIButton 的正确时间是什么时候？当然，我不能在 cellForRowAtIndexPath 末尾释放按钮 - 这会破坏按钮对象，不是吗？到目前为止，我发现所有将按钮添加到单元格的片段似乎都在 cellForRowAtIndexPath 中保持实例化新的 UIButton 对象，这让我有些困惑..

Answer 1

一些事情:

1. 按钮出现在其他地方，因为您对不同类型的单元格使用相同的单元格标识符。每种类型的细胞都应该有自己的标识符。

2. 就按钮消失而言，我不知道为什么会因为 reloadRowsAtIndexPaths 而发生这种情况，但是如果您将按钮移到其他 subview 的前面，您就赢了失去它。

3. 您可能想要自动释放您的 UITextField。 (同样适用于 titleForHeaderInSection 中的 NSString。)

无论如何，cellForRowAtIndexPath 变成这样:

#define kTextFieldTag 100
#define kButtonFieldTag 101

//-----------------------------------------------------------------------------------------
// cellForRowAtIndexPath
//-----------------------------------------------------------------------------------------
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    NSString *cellIdentifier;
    UITableViewCell *cell;

    // Configure the cell...
    switch( [indexPath section] ) 
    {
        case WORKSHEET_SECTION_CLIENT: 
            cellIdentifier = @"CellClient";

            cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];

            if (cell == nil) 
            {
                cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier] autorelease];
            }

            cell.textLabel.text = clientName;
            cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;      
            break;

        case WORKSHEET_SECTION_PERIOD: 
        {
            UIButton *myButton1;

            cellIdentifier = @"CellPeriod";

            cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];

            if (cell == nil) 
            {
                cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier] autorelease];

                // Don't need UIButton alloc because method below does it for us..
                myButton1 = [UIButton buttonWithType:UIButtonTypeRoundedRect];
                myButton1.tag = kButtonFieldTag;

                CGRect cellFrame = [self.tableView rectForRowAtIndexPath:indexPath];

                int nButtonWidth  = 80;
                int nButtonHeight = 30;
                int nActualCellWidth = cellFrame.size.width - 40;
                int nButtonDeltaX = ( nActualCellWidth      - nButtonWidth  ) / 2;
                int nButtonDeltaY = ( cellFrame.size.height - nButtonHeight ) / 2;
                myButton1.frame = CGRectMake( nButtonDeltaX, nButtonDeltaY, nButtonWidth, nButtonHeight );      

                [myButton1 setTitle:@"OK" forState:UIControlStateNormal];

                // PDS: Add delaget for stopwatch clicking..
                [myButton1 addTarget:self action:@selector(buttonClickedStopWatch:) forControlEvents:UIControlEventTouchUpInside];  

                [cell.contentView addSubview:myButton1];      
            }
            else
            {
                myButton1 = (UIButton *)[[cell contentView] viewWithTag:kButtonFieldTag];
            }

            cell.textLabel.text = timeElapsed;
            cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;   
            [[cell contentView] bringSubviewToFront:myButton1];

            break;      
        }

        case 2:
            cellIdentifier = @"Cell2";

            cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];

            if (cell == nil) 
            {
                cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier] autorelease];
            }

            cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
            cell.textLabel.text = @"Amount $130";
            break;      

        case 3:
        {
            cellIdentifier = @"Cell3";

            cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];
            UITextField *myTextField;            

            if (cell == nil) 
            {
                cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier] autorelease];

                myTextField = [[[UITextField alloc] initWithFrame:CGRectMake(20,10,125,25)] autorelease];
                [myTextField setTag:kTextFieldTag];
                myTextField.adjustsFontSizeToFitWidth = NO;
                myTextField.backgroundColor = [UIColor clearColor];
                myTextField.autocorrectionType = UITextAutocorrectionTypeNo;
                myTextField.autocapitalizationType = UITextAutocapitalizationTypeWords;
                myTextField.textAlignment   = UITextAlignmentLeft;
                myTextField.keyboardType    = UIKeyboardTypeDefault;
                myTextField.returnKeyType   = UIReturnKeyDone;
                myTextField.clearButtonMode = UITextFieldViewModeNever;
                //      myTextField.delegate = self;
                myTextField.font = [UIFont systemFontOfSize:14];

                [cell addSubview:myTextField];
            }
            else
            {
                myTextField = (UITextField *)[[cell contentView] viewWithTag:kTextFieldTag];
            }

            // note, theoretically, you could blow away anything that the user typed here
            [myTextField setPlaceholder:@"Type Data Here"];          

            cell.accessoryType = UITableViewCellAccessoryNone;

            cell.textLabel.font = [UIFont systemFontOfSize:14];
            cell.textLabel.numberOfLines = 0;
            break;

        }

        default:
            cellIdentifier = @"CellDummy";

            cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];

            if (cell == nil) 
            {
                cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier] autorelease];
            }

            cell.textLabel.text = @"Dummy";
            break;

    }

    return cell;
}

就个人而言，我可能会将其拆分为单独的方法，但这取决于您。