自动首选最大布局宽度在8.0之前的iOS版本上不可用

Question

I opened an existing iOS project with Xcode6 beta6, and Xcode lists the following warning for both Storyboard and Xib files:

Automatic Preferred Max Layout Width is not available on iOS versions prior to 8.0

I tried addressing the warning by setting the width as explicit like below:

Yet this didn't resolve the warnings. How can they be removed?

Answer 1

Update 3:
This warning can also be triggered by labels that have numberOfLines set to anything but 1 if your deployment target is set to 7.1. This is completely reproducible with new single-view project.

Steps to Reproduce:

1. Create a new single-view, objective-c project
2. Set the Deployment Target to 7.1
3. Open the project's storyboard
4. Drop a label onto the provided view controller
5. Set the numberOfLines for that label to 2.
6. Compile

I've filed the following radar:
rdar://problem/18700567

Update 2:
Unfortunately, this is a thing again in the release version of Xcode 6. Note that you can, for the most part, manually edit your storyboard/xib to fix the problem. Per Charles A. in the comments below:

It's worth mentioning that you can pretty easily accidentally introduce this warning, and the warning itself doesn't help in finding the label that is the culprit. This is unfortunate in a complex storyboard. You can open the storyboard as a source file and search with the regex <label(?!.*preferredMaxLayoutWidth) to find labels that omit a preferredMaxLayoutWidth attribute/value. If you add in preferredMaxLayoutWidth="0" on such lines, it is the same as marking explicit and setting the value 0.

Update 1:
This bug has now been fixed in Xcode 6 GM.

Original Answer
This is a bug in Xcode6-Beta6 and XCode6-Beta7 and can be safely ignored for now.

An Apple engineer in the Apple Developer forums had this to say about the bug:

Preferred max layout width is an auto layout property on UILabel that allows it to automatically grow vertically to fit its content. Versions of Xcode prior to 6.0 would set preferredMaxLayoutWidth for multiline labels to the current bounds size at design time. You would need to manually update preferredMaxLayoutWidth at runtime if your horizontal layout changed.

iOS 8 added support for automatically computing preferredMaxLayoutWidth at runtime, which makes creating multiline labels even easier. This setting is not backwards compatible with iOS 7. To support both iOS 7 and iOS 8, Xcode 6 allows you to pick either "Automatic" or "Explicit" for preferredMaxLayoutWidth in the size inspector. You should:

Pick "Automatic" if targeting iOS 8 for the best experience. Pick "Explicit" if targeting < iOS 8. You can then enter the value of preferredMaxLayoutWidth you would like set. Enabling "Explicit" defaults to the current bounds size at the time you checked the box.

The warning will appear if (1) you're using auto layout, (2) "Automatic" is set for a multiline label [you can check this in the size inspector for the label], and (3) your deployment target < iOS 8.

It seems the bug is that this warning appears for non-autolayout documents. If you are seeing this warning and not using auto layout you can ignore the warning.

Alternately, you can work around the issue by using the file inspector on the storyboard or xib in question and change "Builds for" to "Builds for iOS 8.0 and Later"

Answer 2

To Find the problem label(s) in a large storyboard, follow my steps below.

1. In xCode's Issue Navigator right click on the error and select "Reveal In Log". (Note: @Sam suggests below, look in xCode's report navigator . Also @Rivera notes in the comments that "As of Xcode 6.1.1, clicking on the warning will automatically open and highlight the conflicting label". I haven't tested this).

2. This will show the error with a code at the end of your storyboard file. Copy the value after .storyboard

3. Next, reveal your storyboard as source file.

4. Search. You should be able to tell what label it is from here quite easily by looking at the content.

Once you find the label the solution that worked for me was to set the "preferred width" to 0.

BTW, you can always quickly get the id of an interface item by selecting the item and looking under the identify inspector. Very handy.

Answer 3

You can fix this issue without opening the storyboard as a source . This warning is triggered by UILabels if numberOfLines !=1 and deployment target is < 8.0

HOW TO FIND IT?

1. Go to Issue Navigator (CMD+8) and Select latest built with the warning
2. Locate the warning(s) (search for " Automatic Preferred Max Layout ") and press expand button on the right
   
3. Find the Object ID of the UILabel
4. Open the Storyboard and SEARCH (CMD+f) for the object. It will SELECT AND HIGHLIGHT the UILabel
5. Set Preferred Width = 0 "Explicit" as others suggested

Answer 4

Solution it's quite simple

Just enable Builds for iOS 8 and Later

Answer 5

Now my Xcode version is 6.1. But I got this warning too. it annoys me a lot . after search again and again.I found the solution.

Reason:You must have set your UILabel Lines > 1 in your Storyboard.

Solution: set your UILabel Lines attribute to 1 in Storyboard. restart your Xcode. It works for me, hope it can help more people.

If you really need to show your words more than 1 line. you should do it in the code.

//the words will show in UILabel
NSString *testString = @"Today I wanna set the line to multiple lines. bla bla ......  Today I wanna set the line to multiple lines. bla bla ......"
[self.UserNameLabel setNumberOfLines:0];
self.UserNameLabel.lineBreakMode = NSLineBreakByWordWrapping;
UIFont *font = [UIFont systemFontOfSize:12];
//Here I set the Label max width to 200, height to 60
CGSize size = CGSizeMake(200, 60);
CGRect labelRect = [testString boundingRectWithSize:size options:NSStringDrawingUsesLineFragmentOrigin attributes:[NSDictionary dictionaryWithObject:font forKey:NSFontAttributeName] context:nil];
self.UserNameLabel.frame = CGRectMake(self.UserNameLabel.frame.origin.x, self.UserNameLabel.frame.origin.y, labelRect.size.width, labelRect.size.height);
self.UserNameLabel.text = testString;

Answer 6

总而言之，对于我，按照上面的两条说明将numberOfLines = 0更改为1或更大的任何实例，并手动将optimMaxLayoutWidth =“0”添加到storyboard源内的每个标签实例，修复了我的所有警告。

Answer 7

Since I don't have a 50 reputation Stackoverflow wont let me comment on the second best answer. Found another trick for finding the culprit label in the Storyboard.

So once you know the id of the label, open your storyboard in a seperate tab with view controllers displayed and just do command F and command V and will take you straight to that label :)

Answer 8

I got it working by selecting the original layout I had in the W / H selection. Storyboard is working as expected and the error is gone.

Be also sure that you are developing for iOS 8.0. Check that from the project's general settings.

This is where you should press.

Answer 9

I had this issue and was able to fix it by adding constraints to determine the max with for a label.

When dropping a multiline label in there is not constraint set to enforce the width inside the parent view. This is where the new PreferredMaxWidth comes into play. On iOS 7 and earlier you have to define the max width yourself. I simply added a 10px constraint to the left and right hand side of the label.

You can also add a <= width constraint which also fixes the issue.

So this is not actually a bug, you simply have to define the max width yourself. The explicit option mention in other answer will also work as you are setting this width value however you will have to modify this value if you want the max width to change based on the parent width (as you have explicitly set the width).

My above solution ensures the width is always maintained no matter how big the parent view is.

Answer 10

For some reason, even if changing the iOS Deployment Target to 8.0 or higher, the Xib files don't adopt that change and remain with the previous settings in the File inspector

Therefore, you should change it manually for each Xib

Once done, the warning will disappear :-)