尝试从didSelectItemAtIndexPath中的uilabel访问cellForItemAtIndexPath，但无法获取第一个单元格。这是我的代码
cellForItemAtIndexPath 中的
UICollectionViewCell *cell=[collectionView dequeueReusableCellWithReuseIdentifier:@"Cell" forIndexPath:indexPath];
UILabel *featureName = [[UILabel alloc] initWithFrame:CGRectMake(5, 5, cell.frame.size.width-10, cell.frame.size.height-10)];
featureName.tag = indexPath.row;
[cell addSubview:featureName];
didSelectItemAtIndexPath 中的
UICollectionViewCell *cell = [collectionView cellForItemAtIndexPath:indexPath];
UILabel *featureName = [cell viewWithTag:indexPath.row];
featureName.textColor = [UIColor lightGrayColor];
可以从所有单元格中获取label.tag，但不能从第一个单元格中获取var oldPoly1Matrix;
var canvas = new fabric.Canvas('c');
var srcOptions = {
stroke: 'blue',
fill: '',
type: 'src'
};
var destOptions = {
stroke: 'red',
fill: '',
selectable: false,
hasControls: false,
hasBorders: false,
type: 'dest'
};
var poly1 = new fabric.Polygon([{
x: 60,
y: 40
}, {
x: 160,
y: 40
}, {
x: 160,
y: 140
}, {
x: 60,
y: 140
}], srcOptions);
var poly2 = new fabric.Polygon([{
x: 60,
y: 300
}, {
x: 160,
y: 300
}, {
x: 160,
y: 400
}, {
x: 60,
y: 400
}], destOptions);
canvas.add(poly1).add(poly2);
oldPoly1Matrix = poly1.calcTransformMatrix();
var originalPoly2Matrix = poly2.calcTransformMatrix();
poly2.matrix = originalPoly2Matrix;
function updatePoly2() {
var newPoly1Matrix = poly1.calcTransformMatrix();
var oldPoly1MatrixInverted = fabric.util.invertTransform(oldPoly1Matrix);
//newMatrix = oldMatrix * someMatrix
//therefore,someMatrix = newMatrix / oldMatrix = newMatrix * inverse(oldMatrix);
var diffMatrix = fabric.util.multiplyTransformMatrices(newPoly1Matrix, oldPoly1MatrixInverted);
var oldPoly2Matrix = poly2.matrix;
//Apply the same someMatrix to find out the new transform matrix for poly2.
var newPoly2Matrix = fabric.util.multiplyTransformMatrices(oldPoly2Matrix, diffMatrix);
var updatedPoints = poly2.get('points')
.map(function(p) {
return new fabric.Point(p.x - poly2.minX - poly2.width / 2, p.y - poly2.minY - poly2.height / 2);
})
.map(function(p) {
return fabric.util.transformPoint(p, newPoly2Matrix);
});
oldPoly1Matrix = newPoly1Matrix;
poly2.remove();
poly2 = new fabric.Polygon(updatedPoints, destOptions);
poly2.matrix = newPoly2Matrix;
canvas.add(poly2);
}。点击第一个单元格时应用程序崩溃。
答案 0 :(得分：1)
indexPath.row为0，但0不是有效标记。
我认为你应该只使用非零值。
尝试即。
featureName.tag = indexPath.row + 1;
...
UILabel *featureName = [cell viewWithTag:indexPath.row+1];
答案 1 :(得分：0)
<强> cellForItemAtIndexPath
UICollectionViewCell *cell=[collectionView dequeueReusableCellWithReuseIdentifier:@"Cell" forIndexPath:indexPath];
UILabel *featureName = [[UILabel alloc] initWithFrame:CGRectMake(5, 5, cell.frame.size.width-10, cell.frame.size.height-10)];
featureName.tag = indexPath.row + 1;
[cell addSubview:featureName];
希望这能解决您的问题：）UICollectionViewCell *cell = [collectionView cellForItemAtIndexPath:indexPath];
UILabel *featureName = [cell viewWithTag:indexPath.row + 1 ];
featureName.textColor = [UIColor lightGrayColor];