How do you determine if Pen Input is blank?

[Shanescows]

I want to have a pen input to collect a signature and I only want to show the user the submit button after they have signed the form. 

How do I check if they have scribbled something in the box or not?

Thanks

Shane

[grahampasmurf]

No, I never found a solution. Did that recently mentioned workaround work? If so, how? What was different?

[timl]

Hi @grahampasmurf 

@seadude's solution works for me (well done seadude!).

The OnVisible property of the screen sets the following 2 variables:

Set(varInitialPenInput, PenInput1.Image);
Set(varPenInput, PenInput1.Image)

The OnSelect property of the pen input control sets the varPenInput variable.

Set(varPenInput, PenInput1.Image)

To check for changes, you can compare varInitialPenInput against varPenInput.

If(varInitialPenInput <> varPenInput, 
   "Yes it has", 
   "No it hasn't"
)

[grahampasmurf]

Okay, now I see the difference. I was setting the variables at OnVisible, but I did not see the step about updating the variable at OnSelect.

That will work but there is 1 catch. If the user clicks the X to "reset" the image back to blank, it will allow the user to save a blank image. I will see if there is a way to prevent that.

[grahampasmurf]

Okay, it works now with a nested If statement on DisplayMode

If(varInitialPenInput <> varPenInput, If(varPenInput = PenInput1.Image, DisplayMode.Edit, DisplayMode.Disabled), DisplayMode.Disabled)

After it compares to make sure the initial image is not the same as the "after" image, it also checks to make sure the current value of the image is the same as the "after" image (because current value of the image (PenInput1.Image) will change when the X "reset" is selected, but the OnSelect code does not run when that happens, so that will make the values different and it should be disabled).

[MattyH]

Thanks to you all, I am creating a Powerapp with a signature requirement for the first time, and this has answered every question I had!

[juresti]

This is the only working method for me for Power Apps online.

I have a clear signature button in case the signature is not as expected.

At the time of clear I have to also collect a new blank image to compare against blank since resetting the pen input will create a new image with a different "ID".

[newbie101]

Thanks for the solutions above. Here is a simpler solution. 

1. For App, onStart = Set(varBlank, true)
2. For PenInput1 control,
   1. ShowControls = false
   2. onSelect =  Set(varBlank, false)
3. Add a button on top of PenInput1 control, onSelect = Reset(PenInput1); Set(varBlank, true)

[IvySoe]

It works for me! Thanks.

[Aaron3Sixty5]

Thanks to everyone in this thread.  @newbie101 proves that you never want to go with the first solution: once the ideas start flowing, solutions get posted, and folks much smarter than myself start digging deep into a problem, sometimes an easier or more elegant way to accomplish the same thing is discovered and shared.  Great work by all, thanks!

[Dlabar]

For me, when I attempt to get the image of the pen input in the OnVisible of the screen, it is always blank (null/nothing) on the initial load.  And by the time I click my save button, the control gets an empty image (a value of empty, so something/not null).  Here is my work around (Please note, I showControls = false and a custom "clear/erase" button to reset the pen input control):

Screen.OnVisible:

UpdateContext({ isSigBlank: true });

EraseSignatureBtn.OnSelect:

If(isSigBlank,
    UpdateContext({
        emptySig: JSON(Signature.Image, JSONFormat.IncludeBinaryData)
    });
);

UpdateContext({
    isSigBlank: true
});

Reset(Signature);

Signature.OnSelect:

UpdateContext({
    isSigBlank: false
});

SaveBtn.OnSelect:

If(isSigBlank|| emptySig = JSON(Signature.Image, JSONFormat.IncludeBinaryData),
    Notify("A signature is required!", NotificationType.Error)
,
    // Pen Input is non-empty, do whatever it is that needs to be done
);

If(isSigBlank,
    UpdateContext({
        emptySig: JSON(Signature.Image, JSONFormat.IncludeBinaryData)
    });
);

This allows enforcing that the user has actually drawn something (could be a dot).  Without the emptySig variable, it would allow completely empty signatures.  

This also requires separate isSigBlank and emptySig variables per Pen Input, since the empty images are actually unique per Pen Input control