How to keep always first cell of tableview on top

问题:

I want to keep my first cell always on top of my tableview when scroll.

Any help is appreciable.Thanks in advance...

回答1:

Here is how you create your Header view for your UITableView

- (UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger) section {
    UIView *sectionHeaderView = [[UIView alloc] initWithFrame:
                                     CGRectMake(0, 0,tableView.frame.size.width, 40.0)];
    // Customize it as per your design
    return sectionHeaderView;

}

Now return the height of the

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
    //return the desirable height
    return 40;
}

Hope this helps you.

回答2:

Here is a table view class that can be inherited, to provide a header that sticks to the top of the visible area. It has these key features:

1. You have the option of providing a masking image, is cases where your header has transparency, and you therefore need to hide the scrolled table cells.
2. You can configure the height of the visible header area, from the view controller.

FixedHeaderTableView.h

    /**
     * Table with a fixed header. The header does not scroll off the top of the visible area, and it does not
     * scroll down off the top of the header area. The scroll indicator insets are adjusted to go to the top of
     * the table, below the header view.
     *
     * Instructions for use:
     *
     *    1) Create a table view that inherits from FixedHeaderTableView, and configure it:
     *        - set the delegate to your view controller
     *        - this allows you to implement UITableViewDelegate methods, and UIScrollViewDelegate method,
     *          scrollViewDidScroll:
     *    2) Create a separate UIView with the same width as the table view, to be used as the fixed table header.
     *    3) Implement scrollViewDidScroll: in your UITableViewDelegate, to simply delegate to your FixedHeaderTableView.
     *    4) In viewDidLoad of your view controller, do the following:
     *        - Set the containerView property to the view controller's main view.
     *        - Create or get a masking view, if the table header is not fully opaque. This prevents the table cells
     *          from being shown behind the header view, when they are scrolled up.
     *        - Call setFixedTableHeaderView:visibleHeaderHeight:withMaskingImageView:maskingImageFrame: on your
     *          FixedHeaderTableView.
     */
    @interface FixedHeaderTableView : UITableView {
        UIView *_containerView;
        UIView *_fixedTableHeaderView;
        int _hiddenHeight;

        //Used to mask cells behind a transparent header
        UIImageView *_maskingImageView;
    }

    @property (strong, nonatomic) UIView *containerView;

    /**
     * To be called from the UITableViewDelegate, to delegate header view positioning and masking.
     */
    - (void) scrollViewDidScroll:(UIScrollView *)scrollView;

    /**
     * Should be called from viewDidLoad of the view controller.
     * 

     * This sets and configures the fixed table head view.
     *
     * @param fixedTableHeaderView    UIView that is used as the sticky header
     *
     * @param visibleHeaderHeight     The bottom portion of the header that will stay visible. This can
     *                                be the same height as the header view, or lower. If it is out of
     *                                this range, it is clamped to the closest value (0 or the height).
     *
     * @param maskingImage            This is optional, and it only needed if your header view has
     *                                transparent areas. Using a masking image provides much better
     *                                performance than adjusting the masks of each cell, in the
     *                                scrollViewDidScroll: delegate method.
     *
     * @param maskingImageFrame       If the masking image is provided, this should be set to position
     *                                the background image, so that it is equal to any other image position
     *                                used in the background.
     */
    - (void) setFixedTableHeaderView:(UIView *)fixedTableHeaderView
                 visibleHeaderHeight:(int)visibleHeaderHeight
                    withMaskingImage:(UIImage *)maskingImage
                  maskingImageFrame:(CGRect)maskingImageFrame;

    @end

FixedHeaderTableView.m

    #import “FixedHeaderTableView.h"

    @interface FixedHeaderTableView ()

    @property (assign, nonatomic) int hiddenHeight;
    @property (strong, nonatomic) UIView *fixedTableHeaderView;
    @property (strong, nonatomic) UIImageView *maskingImageView;

    @end

    @implementation FixedHeaderTableView

    - (void) scrollViewDidScroll:(UIScrollView *)scrollView
    {
        CGRect tableHeaderRect = _fixedTableHeaderView.frame;

        //Prevent table header from being dragging down from the top
        tableHeaderRect.origin.y = MIN(0, -scrollView.contentOffset.y);
        tableHeaderRect.origin.y += self.frame.origin.y;

        //Prevent table header from scrolling completely off the top
        if (scrollView.contentOffset.y > _hiddenHeight) {
            tableHeaderRect.origin.y = -_hiddenHeight;
            _maskingImageView.hidden = FALSE;
        } else {
            _maskingImageView.hidden = TRUE;
        }

        self.fixedTableHeaderView.frame = tableHeaderRect;
    }

    - (void) setFixedTableHeaderView:(UIView *)fixedTableHeaderView
                 visibleHeaderHeight:(int)visibleHeaderHeight
                    withMaskingImage:(UIImage *)maskingImage
                  maskingImageFrame:(CGRect)maskingImageFrame
    {
        self.fixedTableHeaderView = fixedTableHeaderView;

        //Quietly ensure the value is not out of acceptable range
        if (visibleHeaderHeight > _fixedTableHeaderView.frame.size.height) {
            visibleHeaderHeight = _fixedTableHeaderView.frame.size.height;
        } else if (visibleHeaderHeight < 0) {
            visibleHeaderHeight = 0;
        }
        self.hiddenHeight = _fixedTableHeaderView.frame.size.height - visibleHeaderHeight;

        //Shift the scrolling insets to span the height of the table's rows
        self.scrollIndicatorInsets = UIEdgeInsetsMake(_fixedTableHeaderView.frame.size.height, 0, 0, 0);

        CGRect tableHeaderFrame = _fixedTableHeaderView.frame;
        tableHeaderFrame.origin.x = self.frame.origin.x;
        tableHeaderFrame.origin.y = self.frame.origin.y;
        _fixedTableHeaderView.frame = tableHeaderFrame;
        [self.superview addSubview:_fixedTableHeaderView];

        self.tableHeaderView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, self.frame.size.width, _fixedTableHeaderView.frame.size.height)];

        //Table header view sits behind the fixed header view
        if (maskingImage) {
            maskingImageFrame.origin.y += _hiddenHeight;
            UIImageView *maskingImageView = [[UIImageView alloc] initWithFrame:maskingImageFrame];
            maskingImageView.image = maskingImage.copy;
            [_fixedTableHeaderView addSubview:maskingImageView];
            [_fixedTableHeaderView sendSubviewToBack:maskingImageView];
            _fixedTableHeaderView.clipsToBounds = TRUE;

            self.maskingImageView = maskingImageView;
            _maskingImageView.hidden = TRUE;
        }
    }

    @end