UITableViewCell - 如何在重用之前重置内容 [英] UITableViewCell - how to reset content before reusing

问题描述

有一个令人讨厌的错误，我无法修复。

我有一个 CustomCell ，并且在其中我有一个子视图，根据对象的值改变它的颜色。

   - （UITableViewCell *）tableView：（UITableView *）tableView cellForRowAtIndexPath ：（NSIndexPath *）indexPath {
 static NSString * cellIdentifier = @CustomCell; 
 
 CustomCell * cell =（CustomCell *）[tableView dequeueReusableCellWithIdentifier：cellIdentifier forIndexPath：indexPath]; 
 
 if（cell == nil）{
 cell = [[CustomCell alloc] initWithStyle：UITableViewCellStyleDefault reuseIdentifier：cellIdentifier]; 
} 
 
 MyObject * object = [self.fetchedResultsController objectAtIndexPath：indexPath]; 
 
 if（[object.redColor isEqualToNumber：[NSNumber numberWithBool：YES]]）{
 cell.colorView.backgroundColor = [UIColor redColor]; 
} 
 else {
 cell.colorView.backgroundColor = [UIColor clearColor]; 
} 
 
返回单元格; 
} 
  

除非我用<$ c $删除一行，否则这一切都正常从tableview中c> redColor = YES ，滚动显示不可见的行。变为可见的第一行（重用可重用单元格的第一行）具有红色，即使该行为 redColor = NO 。如果我再次滚动并隐藏单元格然后再次显示它，颜色将设置为clearColor，它应该是这样的。

我认为这是因为它正在重复使用刚被删除的单元格。
所以我试图在重用之前重置单元格的内容。
在 CustomCell.m

   - （void）prepareForReuse {
 [super prepareForReuse]; 
 
 self.clearsContextBeforeDrawing = YES; 
 self.contentView.clearsContextBeforeDrawing = YES; 
 self.colorView.backgroundColor = [UIColor clearColor]; 
} 
  

但这不起作用。
Apple Doc说

tableView中的表视图委托：cellForRowAtIndexPath：重复使用单元格时应始终重置所有内容。

重置内容的正确方法是什么？我是否必须从超视图中删除子视图？

提前致谢

解决方案

这似乎有效。

我在 CustomCell.m

<中填写prepareForReuse时删除了单元格的contentView pre> - （void）prepareForReuse {
[super prepareForReuse];

//清除contentView
BOOL hasContentView = [self.subviews containsObject：self.contentView];
if（hasContentView）{
[self.contentView removeFromSuperview];
}
}


在中再次添加cellForRowAtIndexPath

   - （UITableViewCell *）tableView：（UITableView *）tableView cellForRowAtIndexPath：（NSIndexPath *） indexPath {
 
 // Cell 
 static NSString * cellIdentifier = @CustomCell; 
 
 CustomCell * cell =（CustomCell *）[tableView dequeueReusableCellWithIdentifier：cellIdentifier forIndexPath：indexPath]; 
 
 if（cell == nil）{
 cell = [[CustomCell alloc] initWithStyle：UITableViewCellStyleDefault reuseIdentifier：cellIdentifier]; 
} 
 
 //恢复contentView 
 BOOL hasContentView = [cell.subviews containsObject：cell.contentView]; 
 if（！hasContentView）{
 [cell addSubview：cell.contentView]; 
} 
 
 //配置单元格
 MyObject * object = [self.fetchedResultsController objectAtIndexPath：indexPath]; 
 
 if（[object.redColor isEqualToNumber：[NSNumber numberWithBool：YES]]）{
 cell.colorView.backgroundColor = [UIColor redColor]; 
} 
 else {
 cell.colorView.backgroundColor = [UIColor clearColor]; 
} 
 
返回单元格; 
} 
  

希望这会对某人有所帮助。

There's an annoying bug that I can't fix.

I have a CustomCell, and in it I have a subview that changes it's color according to object's value.

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *cellIdentifier = @"CustomCell";

    CustomCell *cell = (CustomCell *)[tableView dequeueReusableCellWithIdentifier:cellIdentifier forIndexPath:indexPath];

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

    MyObject *object = [self.fetchedResultsController objectAtIndexPath:indexPath];

    if ([object.redColor isEqualToNumber:[NSNumber numberWithBool:YES]]) {
        cell.colorView.backgroundColor = [UIColor redColor];
    }
    else {
        cell.colorView.backgroundColor = [UIColor clearColor];
    }       

    return cell;
}

This is all working fine except when I delete a row with redColor = YES from the tableview, and I scroll to show rows that was not visible. The first row that becomes visible (first row that reuses the reusable cell) has red color, even though that row is redColor = NO. And if I scroll again and hide the cell and then show it again, color is set to clearColor, the way it should be.

I think this is because it's reusing the cell that has just been deleted. So I'm trying to reset cell's content before reusing. In CustomCell.m

- (void)prepareForReuse {
    [super prepareForReuse];

    self.clearsContextBeforeDrawing = YES;
    self.contentView.clearsContextBeforeDrawing = YES;
    self.colorView.backgroundColor = [UIColor clearColor];
}

But this is not working. Apple Doc says

The table view's delegate in tableView:cellForRowAtIndexPath: should always reset all content when reusing a cell.

What is the proper way to reset content? Do I have to remove subviews from the superview?

Thanks in advance

解决方案

This seems to work.

I remove the cell's contentView when prepareForReuse in CustomCell.m

- (void)prepareForReuse {
    [super prepareForReuse];

    // Clear contentView
    BOOL hasContentView = [self.subviews containsObject:self.contentView];    
    if (hasContentView) {
        [self.contentView removeFromSuperview];
    }
}

Add it in again in cellForRowAtIndexPath

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

    // Cell
    static NSString *cellIdentifier = @"CustomCell";

    CustomCell *cell = (CustomCell *)[tableView dequeueReusableCellWithIdentifier:cellIdentifier forIndexPath:indexPath];

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

    // Restore contentView
    BOOL hasContentView = [cell.subviews containsObject:cell.contentView];
    if (!hasContentView) {
        [cell addSubview:cell.contentView];
    }

    // Configure cell
    MyObject *object = [self.fetchedResultsController objectAtIndexPath:indexPath];

    if ([object.redColor isEqualToNumber:[NSNumber numberWithBool:YES]]) {
        cell.colorView.backgroundColor = [UIColor redColor];
    }
    else {
        cell.colorView.backgroundColor = [UIColor clearColor];
    }       

    return cell;
}

Hope this will help someone.

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