在iOS中使用UIPanGestureRecognizer時嘗試限制UIImage的移動

Question

我正在開發一個允許用戶移動標尺在UITableView上滾動的應用程序。 此刻，標尺移動得很好，只是我想將其移動限制為僅UITableView的行，而沒有別的。 不幸的是，此刻，用戶能夠從頂部滾動整個表格，並超出表格底部到屏幕底部。 我已附上圖片以顯示此內容：

這是我擁有的相關代碼：

    - (void)panGestureDetected:(UIPanGestureRecognizer *)recognizer {

    CGPoint newCenter  = _imageView.center;

        newCenter.y = [recognizer locationInView:[_imageView superview]].y;

        if (newCenter.y - _imageView.frame.size.height / 2 < self.table.frame.origin.y)
            newCenter.y = self.table.frame.origin.y + _imageView.frame.size.height / 2;

        else if (newCenter.y + _imageView.frame.size.height / 2 > self.table.frame.origin.y + self.table.frame.size.height)
            newCenter.y = self.table.frame.origin.y + self.table.frame.size.height - _imageView.frame.size.height / 2;

        _imageView.center = newCenter;


        if ([recognizer state] == UIGestureRecognizerStateChanged) {

            if (newCenter.y == self.table.frame.origin.y + _imageView.frame.size.height / 2) {

                CGPoint topPoint = [recognizer locationInView:_table];
                NSIndexPath *nextRow = [_table indexPathForRowAtPoint:topPoint];
                int currentRow = nextRow.row;

                if (currentRow != 0) {

                    nextRow = [NSIndexPath indexPathForRow:currentRow-- inSection:0];

                    [UIView animateWithDuration:.3 animations:^{
                        [_table selectRowAtIndexPath:nextRow animated:NO scrollPosition:UITableViewScrollPositionBottom];

                    }];

                }


            }
            //below is the specific section where I believe is the issue
            else if (newCenter.y == self.table.frame.origin.y + self.table.frame.size.height - _imageView.frame.size.height / 2) {

                CGPoint bottomPoint = [recognizer locationInView:_table];
                NSIndexPath *nextRow = [_table indexPathForRowAtPoint:bottomPoint];
                int currentRow = nextRow.row;

                if (currentRow != [self.tireCode count]-1) {

                    nextRow = [NSIndexPath indexPathForRow:currentRow++ inSection:0];

                    [UIView animateWithDuration:.3 animations:^{
                        [_table selectRowAtIndexPath:nextRow animated:NO scrollPosition:UITableViewScrollPositionBottom];

                    }];

                }

            }

        }

就像我說的那樣，我希望標尺僅滾動UITableView的行，而沒有其他內容。 我做錯了什么？

Answer 1

在分配超出范圍的值之前，應檢查newCenter.y的值。 為其定義一個最小值和最大值。

float calculatedY = self.table.frame.origin.y + _imageView.frame.size.height / 2;

calculatedY = MAX(calculatedY, MINIMUM_VALUE_HERE);
calculatedY = MIN(calculatedY, MAXIMUM_VALUE_HERE);

newCenter.y = calculatedY;