Error handling

Power Fx language has a new preview feature to enable Formula level error handling. This is by default turned On in the Settings.

This setting gives access to formulas like IfError, IsError, Error, and IsBlankorError. These functions allow you to detect errors, provide alternative values, or take specific actions based on the encountered error.

Validation Error Handling

Above functions can help with validating inputs such as incorrect format or required fields. Use If statements or functions like IsBlank and IsError to validate user input. Provide clear error messages and prevent further processing until the input is corrected.

If( IsBlank(TextInput.Text),
    Notify("Field cannot be blank", 
    NotificationType.Error),
    // Continue with processing
)

Patch Function Error Handling

Similar to the previous example, Error functions can help catch errors while patching data to data source. Patch function reports errors in 2 ways.

It can return an error value as the result of the operations.

UpdateContext(
    {   
    result : Patch(
             Feeds,
             Defaults(Feeds),
             {
                 createdon: Now(),
                 crde8_content: TextInput1_1.Text
                 cr9ce_imageurl: filename
             }
        )
    }
)

Errors can be detected with IsError and replaced or suppressed with IfError

IfError(result, Notify("There was an issue saving data" , NotificationType.Error));
IfError(result, Notify("There was an issue saving data" , & FirstError.Message, NotificationType.Error))

If(
    IsError(
        Patch(
            Feeds,
            Defaults(Feeds),
            {
                createdon: Now(),
                crde8_content: TextInput1_1.Txt,
                cr9ce_imageurl: filename        
            }
        )
    ),
    Notify("Error: There was an issue saving data", NotificationType.Error)
)

Forms Error Handling

When using Forms to submit data via SubmitForm function, using Form control property OnFailure to notify the error message.

// OnSelect property of the form's submit button
SubmitForm(frm_SubmitData);

// OnSuccess property of the form
Navigate('Success Screen');

// OnFailure property of the form
Notify("Error: the invoice could not be created", NotificationType.Error);

Custom Error Message with OnError Property

Power Apps OnError is a property on your app which lets you capture all your unhandled errors. The OnError property gives you the ability to execute an expression that runs every time an error is not handled by the app (such as storing it in a variable or using a function such as IfError to replace it with some other value). To use the OnError property, you need to add it to the app that you want to apply it to. Then, you can specify the error message that you want to display by writing a formula in the OnError property box.

It's important to note that App.OnError can't replace the error in the same way that IfError can. At the point that App.OnError is executed, the error has already happened, and the result has propagated through other formulas. App.OnError only controls how the error is reported to the end user and provides a hook for the maker to log the error if desired.

This code on App.OnError can help locate the source of the error:

Notify(
    Concatenate(
        FirstError.Message,
        ", Observed: ",
        FirstError.Observed,
        ", Source: ",
        FirstError.Source
    ),
    NotificationType.Error
)

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