TextMesh Pro Null Reference Exception with Empty String

TextMesh Pro returns a null reference exception error if I try to reference text that's empty. I get the error even if I try to get the text.length. Unity UI text does not generate such an error, as I discovered when I switched my project over to TMP. Unity text correctly returns an empty string or length of zero. Is there any way to prevent this crash, make TMP behave like Unity text, other than to always make sure TMP text always contains at least one character?

I don't know if this is something different or I never noticed before, but if I define a String variable and don't assign it a value, it returns a null reference error if I try to get its length.

 

It doesn't sound like your TextMeshPro.text is empty, it sounds like it's null. TextMeshPro.text is a simple string property and just like your variable example, if it's null you can't access members such as length on it. If it's an empty string length will work - it's regular C# and not anything TextMesh Pro controls.

Assigning String.Empty to your TextMeshPro.text or checking if it has contents with String.IsNullOrEmpty(myTextMeshProString.text) might help you out.

 

This happens when I don't assign a string to a TMP object. The program starts with nothing in the field (as shown in the Inspector), then gives the error if I try to access the text before putting a string in the field.

I have code that saves the current contents of a text field before changing it, then restores the original contents later. With Unity text, this wasn't a problem, it returns an empty string or length of zero if there's nothing in the the field. When I switched this project over to TMP, it started crashing. So now I have to make sure that TMP text objects always start with something in them, and make sure they're never empty. It's not a serious problem, just TMP behavior that is not the same as regular Unity UI text.

 

I don't know what's going on, but now I can't reproduce the problem. I can only get the null reference error now if I assign an unassigned string to the text object:

var tt: String;
infoText.text = tt;
print(infoText.text); // returns Null, no error
print(infoText.text.length); // null reference error

And now I'm only getting an error when I access the string's length. Previously, I was also getting an error when I accessed the string itself. I'm not sure what I was doing to get the original error, but I didn't start looking at the string length until I started tracking down the error just trying to get the text.

 

Another odd, intermittent problem I've run into after switching a project from Unity UI text to TMP text is with disappearing button text. The attached screen capture shows two buttons in a pop-up dialog panel, the top half shows the Scene view, the bottom half shows the game view. I'm not sure how this is even possible, how the text can be visible in the Scene view but not in the Game view.

I haven't spent too much time trying to track this down yet. I thought it might have something to do with setting the text's alpha (when enabling/disabling the button) while the panel is inactive, but I don't think that's it. This doesn't happen every time the panel is shown, sometimes I have to open and close the panel MANY times to get it to happen, which is why it took me a while to discover the problem. But once the button text disappears, it happens every time the panel is shown after that, even if I stop and restart the game. Once the text disappears, I have to quit and restart Unity to make it come back. I never saw this before I switched the button text to TMP.

I'm not sure how to figure this one out, as I have no idea what could cause the text to be invisible only in the Game view. I never do anything to the buttons, other than reducing the texts' alpha when they're disabled. The buttons/text are never made inactive, only their panel parent.

I just noticed some more text disappearing. This is text that's in another panel. When I open a completely different panel, all the text in this panel disappears. Opening the one panel has nothing to do with the text in the other panel that disappears.

 

I got a chance to look into this, and I have no idea what's going on.

I tracked down the cause of the disappearing text to instantiating one of 4 gameObjects, out of many. There's no difference code-wise between the objects that cause the problem and those that don't. No errors are generated, and everything is initialized properly. That is the one and only line that when commented out fixes the problem. The strange part is, once I instantiate one of those gameObjects and the button text disappears, all text seems to be broken after that, even after I Stop and Play again. When I hit Play after that, any time a panel is shown, it causes text in other visible panels to disappear. If I change something in the code, and then Play, it seems to reset things, but otherwise I have to quit and restart Unity to get back to the point where only the button text disappears. When I say "disappear," I mean only in the Game view, the text is still visible in the Scene view.

To answer your questions:

I only change the color. Below is the code I use to enable/disable buttons. It's the same code I used with Unity UI text, I just changed the component to TMP. I still see the problem even if I comment out all but the first line of that function.

Code (JavaScript):

1. function SetButtonInteractable(theButton: UnityEngine.UI.Button, isEnabled: boolean) {
2.  
3.     theButton.interactable = isEnabled;
4.     if (theButton.GetComponentInChildren(TextMeshProUGUI)) {
5.         var tColor = theButton.GetComponentInChildren(TextMeshProUGUI).color;
6.         if (isEnabled)
7.             tColor.a = 1.0;
8.         else
9.             tColor.a = 0.3;
10.         theButton.GetComponentInChildren(TextMeshProUGUI).color = tColor;
11.     }
12. }

If it is a color/alpha issue, wouldn't you see the same thing in the Game and Scene views?

I'm not scaling any text objects. Other than changing alpha, I'm not doing anything to the text except changing the strings. I'm only changing the alpha on some button text, the other disappearing text never has its alpha changed.

I'm using Unity 2017.3.1f1.

 

I've spent a lot more time on this, and still have no idea what the cause of the problem is.

It looks like it has nothing to do with changing the text's alpha. I've taken out every reference to text alpha, and still the disappearing text. I've taken out everything, all code that is executed from the button click that instantiates the object and opens the panel to the panel showing, with no effect. The only line I delete that fixes the invisible text is the line that instantiates the object.

Code-wise, there's nothing different between instantiating objects that cause the problem and those that don't. Removing the initialization code does nothing. The only difference I can find is that the objects that cause the problem contain a TMP child object (shows the object's ID number), others don't. When those objects are initialized, the TMP object's strings get changed, but nothing else, no color change.

I don't think there's an issue with GetComponentsInChildren. The text objects are never inactive, and it skips setting the alpha if nothing is returned (like for buttons that don't have a text child). This function is only called occasionally, to enable/disable buttons when a panel opens, so it's not a big performance issue.

The last thing I've tried is switching the text back to Unity UI text just for one set of buttons. Problem solved. Since I don't really need any of TMP's special features, I was mainly trying to improve performance, I'm thinking I should cut my losses and switch back to Unity text. I didn't see a difference in batches/setPass calls switching to TMP, though the higher resolution is nice.

 

It's a pretty big project, and I doubt I could strip things out or reproduce it in a simple demo project. The time it will take me to switch the UI back to Unity text will be a lot less than the time I've already spent trying to track this problem down.

One other thing I looked at was the Frame Debugger. I thought the TMP text might just not be updating every frame, which would explain why it's invisible in the Game but not the Scene view. But there's no difference when the text is visible or invisible. _mainTex for TMP text shows <none>. Is that correct? _MainTex for Unity text shows FontTexture. Both show as a draw call in the Frame Debugger, even when the TMP text is invisible.

 

TMP _mainTex always shows <none> in the Frame Debugger, whether the text is currently visible or invisible. Unity text references the font atlas.

I'm trying to submit a bug report. This project has LOTS of unused assets, and it's taking quite a while to pack and upload the report. I'm not sure if it's ever going to finish. After about 90 minutes with the progress bar not moving, I canceled and started over, and it's been uploading now for about 20 minutes. If it ever finishes, I'll post the bug report number.

 

That took WAY too long to upload. Case number 1023353.

I don't think this has anything to do with setting the text color, as I thought at first. It still disappears if I remove all code that changes color or alpha.

 

Have you had a chance to take a look?

 

Thanks. I didn't realize that was an issue, as it did not happen when I was using Unity text for UI and 3D text. When you asked that question, I guess I thought you were referring to having multiple canvases.

So the problem has nothing to do with changing color/alpha, the problem is caused by using the same material for TMP and TMPUGUI objects, correct? That would probably also explain why the two text objects that use a different font were not affected.