Presenting User Error Messages

If you throw a CanvasRenderException from your onRender() implementation, the error message in that exception will be displayed to the user in the Salesforce UI. This exception will be managed only within the onRender() method.

CanvasRenderException supports all the standard Apex exception class methods and constructors. See ”Exception Class and Build-In Exceptions” in the Apex Code Developer Guide for more information on Apex exceptions.

Here’s an example onRender() implementation that throws a Canvas.CanvasRenderException. Salesforce uses this exception and displays “Error: Could not set URL” as the user error message.

public void onRender(Canvas.RenderContext renderContext) {
    // Code omitted that determines if the error condition occured
    ...
    throw new Canvas.CanvasRenderException('Error: Could not set URL.');
}

If the canvas app is run from the Salesforce Chatter tab, the error message resembles: