UITableView : viewForHeaderInSection: not called during reloadData:

Question

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?

Solution 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).

Solution 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 UITableViewDelegate.

That means:

• If you implement the methods but assign yourself only as the dataSource for the UITableView, your tableView:viewForHeaderInSection implementation will be ignored.

• 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.

I have also tried removing tableView:heightForHeaderInSection:; it worked fine and didn't seem to affect the procedures above. But the documentation says that it is required for the tableView:viewForHeaderInSection to work correctly; so to be safe it is wise to implement this, as well.

Solution 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.

Solution 4

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

Solution 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.

View more solutions

Comments

[rmaddy]

Make sure there isn't a typo in the method's signature. One wrong letter will mean it won't be called. Check the case too. Also make sure you are returning 0 from numberOfSections.

[inforeqd]

everything is correct and compiles correctly.. the issue I wanted to understand is around the timing of when the method is called .. tableView:viewForHeaderInSection is called when the table is just about to be displayed and not as part of the synch execution of [tableview reloadData]

[rmaddy]

From the docs for tableView:viewForHeaderInSection:: " This method only works correctly when tableView:heightForHeaderInSection: is also implemented.".

[matt]

Fine. What the docs say, they say. Now experiment. The facts are as I have stated.

[rmaddy]

And how can you have both titleForHeaderInSection and viewForHeaderInSection? The table view will only call one of the two (I forget which gets precedence at the moment).

[matt]

Actually there is one more piece of the puzzle, which is that sometimes viewForHeader is called without any of those three ways of assigning a height. I have had this happen, where my viewForHeader was called and headers showed up just fine, until one day, with no change on my part, they didn't. That's when I started experimenting to discover what the minimal requirements are for viewForHeader to be called. And now I know. And now so do you.

[matt]

If both titleForHeaderInSection and viewForHeaderInSection are implemented, and assuming viewForHeaderInSection returns a UITableViewHeaderFooterView, they will both be called, and in fact this is a perfectly reasonable thing to do.

[testing]

Now I tried to implement titleForHeaderInSection together with viewForHeaderInSection (whereas I only need the view). It works as matt stated but what should titleForHeaderInSection return? It only worked for me when returning an empty space. So it's still a compromise because I have to additionaly return things (height or space).

[casillas]

@matt, do you have any clue for the following stackoverflow.com/questions/34665313/…

[matt]

@texas No, I don't do xamarin. Adding another level of indirection on top of the Cocoa frameworks would just make my head explode. :)

[casillas]

:-) Just ignore about xamarin, my question is simply that my implementation always calls TitleHeader but not calling ViewHeight and ViewHeader. What might be reason?

[GreatWiz]

if you set estimatedSectionHeaderHeightto some value, tableView:viewForHeaderInSection will be called (similarly to how auto dimensions for rows works)

[Benjohn]

Interesting, thanks. Back at 7.1 this subtlety of estimated height was important for cells, so might have been the case for headers too – but it's not terribly relevant now!

[denis631]

You made my day!!! Forgot to assign UITableViewDelegate to self, because I thought, that tableView:viewForHeaderInSection is a UITableViewDataSource method. Thank you!

[Happiehappie]

@maddy OMG Thank you, it's so stupid of me i created my instances but I didn't append to my array

[romrom]

You can absolutely have both. viewForHeaderInSection: will have precedence over titleForHeaderInSection: The only requirement is that you set estimatedSectionHeaderHeight on your table view with something different than 0, otherwise viewForHeaderInSection: will never get called

[zevij]

My issue started after upgrading to Swift 3.1. This solution fixed it.

[Karlis]

Have you tested that your answer actually works? Becaus eif you read carefully then it's stated that initially the viewForHeaderInSection is called. It's not called only when the table is reloaded!

[mfaani]

Any reason you excluded estimatedSectionHeaderHeight from your three ways?

[mfaani]

"tableView:viewForHeaderInSection" is not vital. What's vital is you somehow return a height. You could achieve that through either 1. estimate or 2. a hardcoded value or 3. a titleForHeader which has an intrinsic size. The intrinsic size is calculated based on the Font Family and size.

[matt]

@Honey Look at the date on that answer.

[mfaani]

Ouch/hah. Didn't know. You have look at the date I started developing :) but I guess adding that to the answer won't bother.

[Sharukh Mastan]

@pbuchheit Apple Docs says it is available from iOS 7.0+, please have a look here, developer.apple.com/documentation/uikit/uitableview/…

[pbuchheit]

@Sharukh Mastan Looks like you are correct. For some reason I was getting a warning when I tried using that property, but it went away after doing a clean build.

[Ortwin Gentz]

Adding to @romrom's comment: if you have implemented both titleForHeaderInSection: and viewForHeaderInSection: and the view returned from the latter is a subclass of UITableViewHeaderFooterView then its textLabel.text is automatically set to the all-caps version of the titleForHeaderInSection: string. To prevent this behavior, either don't implement titleForHeaderInSection: or use a custom label instead of the inherited textLabel.

[Victor Engel]

I've just encountered a situation where only one of the headers isn't called. The heightForHeaderInSection is called for all sections, but the viewForHeaderInSection is not called for one of the sections. Which one? The one where the included textfield was just edited. Why does it need to be called? Because the editing could cause the section sort to change. When the data is updated, it is sorted, so I want to redisplay ALL sections, including the section just edited. Weirdly, that is the one that is skipped even though height is queried.