Getting a NoSuchMethodError in Dart

问题:

I'm pretty new to Dart, and I'm used to working with C# (and XNA usually), so Dart is a little different, and I'm not sure why this error is happening.

double left = c.Position.x - (canvasDimensions.x * 0.5);

the Position and canvasDimensions are a type I created, called Vector2, which basically contains 2 numbers, x and y, I am getting the error

NoSuchMethodError : method not found: '-'
Receiver: null
Arguments: [600.0]

on the line shown, since I am not familiar with the language I am not sure why this is happening, please help, thanks!

回答1:

Here c.Position.x is null. In Dart calling a method (or an operator - in your case) on null leads to a NoSuchMethodError.