UICollectionView单元格选择和单元重用 [英] UICollectionView cell selection and cell reuse

问题描述

在选择单元格时，我想处理更改单元格外观的操作.我想到了委托方法collectionView:didSelectItemAtIndexPath:& collectionView:didDeselectItemAtIndexPath:是我应该在其中编辑单元格的地方.

Upon cell selection, I want to handle changing the cell appearance. I figured the delegate method collectionView:didSelectItemAtIndexPath: & collectionView:didDeselectItemAtIndexPath: is where I should edit the cell.

-(void)collectionView:(UICollectionView *)collectionView 
       didSelectItemAtIndexPath:(NSIndexPath *)indexPath {

    DatasetCell *datasetCell = 
      (DatasetCell *)[collectionView cellForItemAtIndexPath:indexPath];

    [datasetCell replaceHeaderGradientWith:[UIColor skyBlueHeaderGradient]];
    datasetCell.backgroundColor = [UIColor skyBlueColor];
}

和

-(void)collectionView:(UICollectionView *)collectionView 
       didDeselectItemAtIndexPath:(NSIndexPath *)indexPath {

    DatasetCell *datasetCell = 
      (DatasetCell *)[collectionView cellForItemAtIndexPath:indexPath];

    [datasetCell replaceHeaderGradientWith:[UIColor grayGradient]];
    datasetCell.backgroundColor = [UIColor myDarkGrayColor];
}

这正常工作，除非重新使用单元格.如果我选择索引为(0，0)的单元格，它将改变外观，但是当我向下滚动时，处于选中状态的另一个单元格.

This works fine, except when the cell gets reused. If I select cell at index (0, 0), it changes the appearance but when I scroll down, there is another cell in the selected state.

我相信我应该使用UICollectionViewCell方法-(void)prepareForReuse来准备要重用的单元格(即，将单元格的外观设置为非选定状态)，但这给我带来了困难.

I believe I should use the UICollectionViewCell method -(void)prepareForReuse to prep the cell for resuse (ie, set the cell appearance to non selected state) but its giving me difficulties.

-(void)prepareForReuse {
    if ( self.selected ) {
        [self replaceHeaderGradientWith:[UIColor skyBlueHeaderGradient]];
        self.backgroundColor = [UIColor skyBlueColor];
    } else {
        [self replaceHeaderGradientWith:[UIColor grayGradient]];
        self.backgroundColor = [UIColor myDarkGrayColor];
    }
}

当我滚动回到顶部时，索引为(0，0)的单元格处于取消选择状态.

When I scroll back to the top, the cell at index (0, 0) is in the deselected state.

当我刚刚使用cell.backgroundView属性时，要防止这种情况发生，是:

When I just used the cell.backgroundView property, to prevent this from happening was to:

-(void)prepareForReuse {
    self.selected = FALSE;
}

并且选择状态按预期工作.

and the selection state worked as intended.

有什么想法吗?

推荐答案

您的观察是正确的.由于单元的重用而发生这种现象.但是您不必使用 prepareForReuse 做任何事情.而是在 cellForItem 中签入并相应地设置属性.像..

Your observation is correct. This behavior is happening due to the reuse of cells. But you dont have to do any thing with the prepareForReuse. Instead do your check in cellForItem and set the properties accordingly. Some thing like..

 - (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"cvCell" forIndexPath:indexPath];


if (cell.selected) {
     cell.backgroundColor = [UIColor blueColor]; // highlight selection 
}
else
{
     cell.backgroundColor = [UIColor redColor]; // Default color
}
return cell;
}

-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath  {

    UICollectionViewCell *datasetCell =[collectionView cellForItemAtIndexPath:indexPath];
    datasetCell.backgroundColor = [UIColor blueColor]; // highlight selection
 }  

 -(void)collectionView:(UICollectionView *)collectionView didDeselectItemAtIndexPath:(NSIndexPath *)indexPath {

UICollectionViewCell *datasetCell =[collectionView cellForItemAtIndexPath:indexPath]; 
datasetCell.backgroundColor = [UIColor redColor]; // Default color
}

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