objc xcode设置uitableview单元格的y起始位置

Question

I have a question about the usage of UITableView. I have added a UIView above the cells of my UITableView (see image).

This is very nice because I can add some images and labels there and it will scroll with the cells of the table view. Now I am calling some REST API to get an image which I want to add in this view above the cells. The problem now is that I dont know the height of the image, so I have to calculate it based on the aspect ratio which already works fine. When I add the image I can change its height correctly and move down labels and buttons BUT the image overlaps some of the visible cells.

My question: How can I move down the frame of the container? of the cells? dynamically based on my image respective View height? I have tried to set the height of the View in the TableView but it has no effect. So I suppose that I have to set the y start position of the cells but I dont know how. Do I need to set an y offset in the delegate method -(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath ? Any ideas?

Answer 1

I think the key to this is setting your view to be the table view's tableHeaderView after you change the size of the view. I did it like this in a test app,

-(void)layoutHeader {
    self.label.text = @"This is a long text to see if it expands to take up multple lines. The quick red fox jumped over the lazy brown dog.";
    [self.label setPreferredMaxLayoutWidth:self.tableView.frame.size.width];
    CGRect stringRect = [self.label.text boundingRectWithSize:CGSizeMake(self.tableView.bounds.size.width - 40,CGFLOAT_MAX) options:NSStringDrawingUsesLineFragmentOrigin attributes:@{NSFontAttributeName:self.label.font} context:nil];
    CGRect headerFrame = self.header.frame;
    headerFrame.size.height = stringRect.size.height + 40;
    self.header.frame = headerFrame;
    [self.tableView beginUpdates];
    self.tableView.tableHeaderView = self.header;
    [self.tableView endUpdates];
}

I called this with a delay from viewDidLoad as a test. The beginUpdates, endUpdates code isn't necessary if you don't want to see the rows move down to accommodate the new view size. The property, header, is an IBOutlet to the view I added to the top of the table view in IB, and "label" is a subview of that view.

Answer 2

I would personally just use tableView:viewForHeaderInSection: to build the view out, and in tableView:heightForHeaderInSection: calculate the new height and return that. That way you don't have to worry about bumping things down within the tableView since UITableView will handle the rest for you once you. Just make sure to call [_tableView reloadData]; on your tableView after you get the image.