UITableView继承自UIScrollview,是苹果为我们封装好的一个基于scroll的控件。上面主要是一个个的UITableViewCell,可以让UITableViewCell响应一些点击事件，也可以在UITableViewCell中加入UITextField或者UITextView等子视图，使得可以在cell上进行文字编辑。
UITableView中的cell可以有很多，一般会通过重用cell来达到节省内存的目的:通过为每个cell指定一个重用标识符(reuseIdentifier),即指定了单元格的种类,当cell滚出屏幕时,会将滚出屏幕的单元格放入重用的queue中，当某个未在屏幕上的单元格要显示的时候，就从这个queue中取出单元格进行重用。
但对于多变的自定义cell，有时这种重用机制会出错。比如，当一个cell含有一个UITextField的子类并被放在重用queue中以待重用，这时如果一个未包含任何子视图的cell要显示在屏幕上，就会取出并使用这个重用的cell显示在无任何子视图的cell中，这时候就会出错。
常规配置如下 当超过tableView显示的范围的时候 后面显示的内容将会和前面重复
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
NSString *identifier=@"aaa";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:identifier];
if (cell == nil) {
cell = [[UITableViewCell alloc]initWithStyle:UITableViewCellStyleDefault reuseIdentifier:identifier];
}
if (indexPath.row%2 == 0) {
cell.textLabel.text = [dataArr objectAtIndex:indexPath.row];
cell.imageView.image = [photoArr objectAtIndex:indexPath.row];
cell.backgroundColor = [UIColor greenColor];
}else
{
self.leftLabel = [[UILabel alloc]initWithFrame:CGRectMake(280, 0, 40, 40)];
self.leftLabel.text = [dataArr objectAtIndex:indexPath.row];
[cell addSubview:self.leftLabel];
self.leftimageView = [[UIImageView alloc]initWithFrame:CGRectMake(320, 0, 66, 44)];
self.leftimageView.image = [photoArr objectAtIndex:indexPath.row];
[cell addSubview:self.leftimageView];
cell.backgroundColor = [UIColor yellowColor];
}
return cell;
}
方案一 取消cell的重用机制，通过indexPath来创建cell 将可以解决重复显示问题 不过这样做相对于大数据来说内存就比较吃紧了
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = @"Cell";
UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];
if (cell == nil) {
cell = [[UITableViewCell alloc]initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier];
}
if (indexPath.row%2 == 0) {
cell.textLabel.text = [dataArr objectAtIndex:indexPath.row];
cell.imageView.image = [photoArr objectAtIndex:indexPath.row];
cell.backgroundColor = [UIColor greenColor];
}else
{
self.leftLabel = [[UILabel alloc]initWithFrame:CGRectMake(280, 0, 40, 40)];
self.leftLabel.text = [dataArr objectAtIndex:indexPath.row];
[cell addSubview:self.leftLabel];
self.leftimageView = [[UIImageView alloc]initWithFrame:CGRectMake(320, 0, 66, 44)];
self.leftimageView.image = [photoArr objectAtIndex:indexPath.row];
[cell addSubview:self.leftimageView];
cell.backgroundColor = [UIColor yellowColor];
}
return cell;
}
方案二 让每个cell都拥有一个对应的标识 这样做也会让cell无法重用 所以也就不会是重复显示了 显示内容比较多时内存占用也是比较多的和方案一类似
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
NSString *CellIdentifier = [NSString stringWithFormat:@"cell%ld%ld",indexPath.section,indexPath.row];
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[UITableViewCell alloc]initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
}
if (indexPath.row%2 == 0) {
cell.textLabel.text = [dataArr objectAtIndex:indexPath.row];
cell.imageView.image = [photoArr objectAtIndex:indexPath.row];
cell.backgroundColor = [UIColor greenColor];
}else
{
self.leftLabel = [[UILabel alloc]initWithFrame:CGRectMake(280, 0, 40, 40)];
self.leftLabel.text = [dataArr objectAtIndex:indexPath.row];
[cell addSubview:self.leftLabel];
self.leftimageView = [[UIImageView alloc]initWithFrame:CGRectMake(320, 0, 66, 44)];
self.leftimageView.image = [photoArr objectAtIndex:indexPath.row];
[cell addSubview:self.leftimageView];
cell.backgroundColor = [UIColor yellowColor];
}
return cell;
}
方案三 只要最后一个显示的cell内容不为空，然后把它的子视图全部删除，等同于把这个cell单独出来了 然后跟新数据就可以解决重复显示
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = @"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; //出列可重用的cell
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
if (indexPath.row%2 == 0) {
cell.textLabel.text = [dataArr objectAtIndex:indexPath.row];
cell.imageView.image = [photoArr objectAtIndex:indexPath.row];
cell.backgroundColor = [UIColor greenColor];
}else
{
self.leftLabel = [[UILabel alloc]initWithFrame:CGRectMake(280, 0, 40, 40)];
self.leftLabel.text = [dataArr objectAtIndex:indexPath.row];
[cell addSubview:self.leftLabel];
self.leftimageView = [[UIImageView alloc]initWithFrame:CGRectMake(320, 0, 66, 44)];
self.leftimageView.image = [photoArr objectAtIndex:indexPath.row];
[cell addSubview:self.leftimageView];
cell.backgroundColor = [UIColor yellowColor];
}
return cell;
}