[SOLVED] Invalid Constant Value using variable as parameter

Invalid Constant Value using variable as parameter

var textSize = 10.0;
// or
double textSize = 10.0;

into Text Widget of Flutter

child: const Text('Calculate Client Fees',
                   style: TextStyle(fontSize: textSize),)

Here it is giving error

Invalid Constant Value

Do we have to compulsory use const value? Why can not we use var or double?

Solution

You are declaring your Text widget as a const, which requires all of its children to be const as well. If you want to fix this, you should not use a const Text widget in this case as you want to pass a non-const variable.

The reason for this is that Flutter uses the const keyword as an indicator for a widget that never updates as it will get evaluated at compile time and only once. Hence, every parameter passed to it has to be constant as well.

double textSize = 10.04;
// ...
child: Text('Calculate Client Fees', style: TextStyle(fontSize: textSize))

This means the widget will never rebuild due to an update of its parameters but only due to internal state changes.