UITableView : viewForHeaderInSection: not called d

问题:

I've set up the tableview with correct delegate and datasource linkages.. the reloadData method calls the datasource and the delegate methods except for viewForHeaderInSection:.

Why is that so?

回答1:

The use of tableView:viewForHeaderInSection: requires that you also implement tableView:heightForHeaderInSection:. This should return an appropriate non-zero height for the header. Also make sure you do not also implement the tableView:titleForHeaderInSection:. You should only use one or the other (viewForHeader or titleForHeader).

回答2:

The trick is that those two methods belong to different UITableView protocols:

tableView:titleForHeaderInSection: is a UITableViewDataSource protocol method, where tableView:viewForHeaderInSection belongs to the protocol UITableViewDelegate (I wonder why, any comments?)

That means

1. If you implement the methods but assign yourself only as the dataSource for the UITableView, tableView:viewForHeaderInSection implementation of yours will be ignored and will never be called.

2. tableView:viewForHeaderInSection has a higher priority. If you implement both of the methods and assign yourself as both the dataSource and the delegate for the UITableView, you will return the views for section headers but your tableView:titleForHeaderInSection: will be ignored.

3. For research purposes, I have removed my tableView:heightForHeaderInSection:; it worked fine and didn't seem to affect the procedures above. But the comment doc states that it is required for the tableView:viewForHeaderInSection to work correctly; so to be safe it is wise to implement this.

回答3:

@rmaddy has misstated the rule, twice: in reality, tableView:viewForHeaderInSection: does not require that you also implement tableView:heightForHeaderInSection:, and also it is perfectly fine to call both titleForHeader and viewForHeader. I will state the rule correctly just for the record:

The rule is simply that viewForHeader will not be called unless you somehow give the header a height. You can do this in any combination of three ways:

• Implement tableView:heightForHeaderInSection:.

• Set the table's sectionHeaderHeight.

• Call titleForHeader (this somehow gives the header a default height if it doesn't otherwise have one).

If you do none of those things, you'll have no headers and viewForHeader won't be called. That's because without a height, the runtime won't know how to resize the view, so it doesn't bother to ask for one.

回答4:

Giving estimatedSectionHeaderHeight and sectionHeaderHeight values fixed my problem. e.g., self.tableView.estimatedSectionHeaderHeight = 100 self.tableView.sectionHeaderHeight = UITableViewAutomaticDimension

回答5:

Going off rmaddy 's answer, I was trying to hide the Header view and was returning 0.0f for "tableView:heightForHeaderInSection" and a 0 height View from tableView:viewForHeaderInSection .

After changing from return 1.0f to return 0.0f in tableView:heightForHeaderInSection, the delegate method tableView:viewForHeaderInSection was indeed called.

Turns out my desired effect works without having to use "tableView:heightForHeaderInSection"; but this may be useful to others who are having an issue getting "tableView:heightForHeaderInSection" delegate method called.

回答6:

You should implement tableView:heightForHeaderInSection: and set the height for the header >0.

This delegate method goes along with the viewForHeaderInSection: method.

I hope this helps.

- (CGFloat)tableView:(UITableView *)tableView heightForHeaderInSection:(NSInteger)section {
         return 40;
}

回答7:

It's worth briefly noting that if your implementation of tableView:heightForHeaderInSection: returns UITableViewAutomaticDimension, then tableView:viewForHeaderInSection: will not be called.

UITableViewAutomaticDimension assumes that a standard UITableViewHeaderFooterView will be used that is populated with the delegate method tableView:titleForHeaderInSection:.

From comments in the UITableView.h:

Returning this value from tableView:heightForHeaderInSection: or tableView:heightForFooterInSection: results in a height that fits the value returned from tableView:titleForHeaderInSection: or tableView:titleForFooterInSection: if the title is not nil.

回答8:

I've just had an issue with headers not showing for iOS 7.1, but working fine with later releases I have tested, explicitly with 8.1 and 8.4.

For the exact same code, 7.1 was not calling any of the section header delegate methods at all, including: tableView:heightForHeaderInSection: and tableView:viewForHeaderInSection:.

After experimentation, I found that removing this line from my viewDidLoad made headers re-appear for 7.1 and did not impact other versions I tested:

// _Removing_ this line _fixed_ headers on 7.1
self.tableView.estimatedSectionHeaderHeight = 80;

… so, there seems to be some kind of conflict there for 7.1, at least.

回答9:

Same issue occured with me but as I was using automatic height calculation from xCode 9, I cannot give any explicit height value as mentioned above. After some experimentation I got solution, we have to override this method as,

-(CGFloat)tableView:(UITableView *)tableView 
         estimatedHeightForHeaderInSection:(NSInteger)section
{
      return 44.0f;
}

Although I have checked both options

1. Automatic Height Calculation
2. Automatic Estimated Height Calculation

from storyboard as apple says, but still I got this weird error.

Please Note: This Error was shown only on IOS-10 version not on IOS-11 version. Maybe it's a bug from xCode. Thanks

回答10:

Here's what I've found (Swift 4) (thanks to this comment on another question)

Whether I used titleForHeaderInSection or viewForHeaderInSection - it wasn't that they weren't getting called when the tableview was scrolled and new cells were being loaded, but any font choices I made for the headerView's textLabel were only appearing on what was initially visible on load, and not as the table was scrolled.

The fix was willDisplayHeaderView:

func tableView(_ tableView: UITableView, willDisplayHeaderView view: UIView, forSection section: Int) {
    if let header = view as? UITableViewHeaderFooterView {
        header.textLabel?.font = UIFont(name: yourFont, size: 42)
    }
}

回答11:

Sometimes setting tableview.delegate or datasource = nil in the viewWillAppear: or viewDidAppear: methods can cause this issue. Make sure not to do this...

回答12:

I had cut & paste the following two methods from a Swift 2 project into my Swift 3 project which were never called because in Swift 3 these methods must have "-" before the first parameter name.

func tableView(tableView: UITableView, heightForHeaderInSection section: Int) -> CGFloat {
    return 44.0
}

func tableView(tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {

    let headerView = tableView.dequeueReusableHeaderFooterView(withIdentifier: B2BTrolleyHeaderFooterView.reuseIdentifier) as! B2BTrolleyHeaderFooterView        
    return headerView
}