iOS8 - constraints ambiguously suggest a height of

问题:

Has anyone got any idea how to debug this?

Warning once only: Detected a case where constraints ambiguously suggest a height of zero for a tableview cell's content view. We're considering the collapse unintentional and using standard height instead.

The rows have a fixed height as set by

- (CGFloat)tableView:(UITableView *)tableView 
           heightForRowAtIndexPath:(NSIndexPath *)indexPath{
   return 34.0;
}

And all the constraints seem to be happy...

回答1:

Forcing a return height and estimated height made the warning disappear in my case.

- (CGFloat)tableView:(UITableView *)tableView 
           estimatedHeightForRowAtIndexPath:(NSIndexPath *)indexPath {
    return 44;
}

- (CGFloat)tableView:(UITableView *)tableView 
           heightForRowAtIndexPath:(NSIndexPath *)indexPath {
    return 44;
}

Another solution where you don't need the two overrides is simply to use self.tableView.rowHeight = 44; in your loadView or init method.

回答2:

What can also be done is adding vertical constraints from the top and to the bottom of the content view. This will make autolayout happy (because he now knows how to calculate the height of the cell himself).

回答3:

If you're using autoLayout constraints and UITableViewAutomaticDimension, this error is not some erroneous problem to be discarded by overriding your height in code. It means that determining the cell height automatically isn't working because you don't have the proper vertical constraints needed.

If you're like me and were getting this error and needed help identifying which cell was throwing the error, you can add the following line right before the return of your 'heightforRowAtIndexPath' method.

NSLog(@"Section %ld Row %ld", (long)[indexPath section], (long)[indexPath row]);

This will print out a long list of sections and rows, but the error will appear immediately following the particular cell that is causing the error, and you can quickly identify which cell is causing the problem and fix your constraints accordingly. This is particularly helpful for static cells. Overriding the height with a manually entered number will work if you're not using autoLayout and automatic cell heights, but will essentially disable these features which is a very poor solution if its something you're trying to utilize.

If you weren't previously using the 'heightForRowAtIndexPath' method but want to debug this error without undoing your UITableViewAutomaticDimension setting, simply add this to your code:

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
    NSLog(@"Section %ld Row %ld", (long)[indexPath section], (long)[indexPath row]);
    return UITableViewAutomaticDimension;
}

回答4:

There appears to be a bug in XCode 6.1 that causes this problem if using auto-layout and you don't specify a value for the Row Height for each Table View Cell, but instead you leave the "default" value. Simply checking the "Custom" checkbox next to the Row Height, for every cell, makes the warning go away.

回答5:

Yes, You get all constrains "happy" even in case when you only have horizontal constrains for items in table view cell. I had same issue. You need to add also vertical constrains. Doing so, that warning will go away.

回答6:

The constraints can be happy for the purpose of layout, but not happy for the purpose of automatic row height. A happy layout would mean the content can be laid out without ambiguity. That would satisfy the checks in Interface Builder.

A happy layout for automatic row height would mean that, in addition to the above, you're also including constraints to the bottom of the cell.

More here: Detected a case where constraints ambiguously suggest a height of zero

回答7:

I used Row Height 43 (or <> 44) in the Table View size inspector and the error disappeared. Using 44 I get the error. Xcode version 6.0.1.

-- This answer was removed by a moderator, please don't, it fixes the problem. This SOLVES the problem for me and may do it for others too. So could you be so kind not to delete it again.

回答8:

I couldn't get to remove the warning, but to make constraints work I set the ,new to iOS8 , tableview property estimatedRowHeight to the fixed height, and removed heightForRowAtIndexPath implementation.

回答9:

If you're getting that warning, it's most likely because you're using auto layout and your cells don't have any constraints inside them.

You should either stop using auto layout or implement constraints that unambiguously define the height of the cells.

You can turn auto layout off in interface builder by unchecking the "Use Autolayout" option in the file inspector on the right.

If you choose to use auto layout and the height of your cells is fixed, implementing the appropriate constraints should be easy. Simply add height constraints for subviews of the cell's content view, and implement vertical space constraints between the subviews, and between the subviews and the content view. For example if your cell has one label in it, this would work:

Vertical constraints

1. Vertical space constraint between the top of the content view and the top of the label
2. Fixed height constraint of label
3. Vertical space constraint between the bottom of the label and the bottom of the content view

Horizontal constraints

1. Horizontal space constraint between the leading edge of the content view and the leading edge of the label
2. Fixed width constraint of label
3. Horizontal space constraint between the trailing edge of the label and the trailing edge of the content view

回答10:

You can use AutoLayout to calculate the right height for you. Here is a nice post about Dynamic Cell Height on iOS 8: http://natashatherobot.com/ios-8-self-sizing-table-view-cells-with-dynamic-type/

回答11:

In Swift forcing a return height fixed my problem:

override func tableView(tableView: UITableView, heightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
    if(indexPath.row == 0){
       return CGFloat(131.0)
    }else if(indexPath.row == 8){
       return CGFloat(97.0)
    }else{
       return CGFloat(44.0)
    }
}

回答12:

For a bog standard fix, no constraints, no estimating heights, or over engineering the problem. I created a default project, wired up the tableview but forgot to put the height delegate in the view controller. To simply make this warning go away you need this.

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath{
    return 44;
}

In your table's view controller.

回答13:

I was using a mapView inside uitableviewcell. I changed the height of map view to 1/3th of the device screen size. I got the same error. I fixed the error by adding missing constraints to the content view of the uitableviewcell.

1) Clear the contentView constraints.

2) Set Reset to Suggested constants to contentView.

3) Add missing constraints - if any

4) We make sure the content view has all the required constraints.

回答14:

In my case, it is because I'm designing the cell with xib, and I forget to add that xib file to the target.

After I add that xib file to the target, the problem is gone

回答15:

While the answers on this page discussing adding height constraints or manually returning rowHeights like 44 in heightForRowAtIndexPath cause the warning to go away, they are superfluous because this is a bug in Xcode visible in at least Version 6.3.2 (6D2105).

If you set a breakpoint in viewDidLoad, you'll see that self.tableView.rowHeight = -1 (UITableViewAutomaticDimension) even if you specify a row height of 44 in the storyboard. This is because Apple incorrectly assumes that you want dynamic row heights if you leave the row height at 44, because they didn't provide a flag for you to specify your preference.

Here are some possible solutions and their results:

• Set row height to 43 or 45 in storyboard (works).

• Manually return a height of 44 in heightForRowAtIndexPath (works).

• Add height constraints between the UITableViewCell’s elements and its contentView (works).

Unfortunately, these solutions either require you to change your design, add unnecessary constraints or add unnecessary code to work around a bug. I tried (what I thought to be) the simplest solution:

• Set each UITableViewCell’s height to 44 (Custom) in the storyboard (fails).

I really wanted a pure storyboard solution to this, so finally I tried:

• Add a user-defined runtime attribute to the UITableView in the storyboard, and name the UITableView with a note about how its rowHeight is being set so future developers can find it: (works):



These bugs are all too common in iOS development and force developers to spend excessive time weighing the ramifications of how their solutions will affect maintainability in the long run.

Since finding a conceptually correct solution that is maintainable and doesn’t seem obfuscated is so elusive, and assuming that Apple will fix the bug and that 44 is going to be the default row height for the foreseeable future, then the constraint or user-defined runtime attribute solutions are probably the most maintainable.

回答16:

There are two important things happening here, I think.

1) It's super easy to make the constraints wrong if you're ctrl+dragging. So, double check that you have it done correctly. Best to use the tray on the left side of the screen to draw these constraints.

2) Instead of specifying the estimatedRowHeight in ViewDidLoad or somewhere else, use the delegate method

override func tableView(tableView: UITableView, estimatedHeightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {}

This fixed the problem right away for me.

回答17:

I've also seen this error when using universal storyboards or xibs. If you neglect to specify proper constraints for the Any x Any size class, I've seen this error appear.

Apple seems to have fixed this for iOS9. The error only happened on 8.4 for me.