Unable to enter variable to SliverAppBar title value-CodePudding

I have an application. I've added a page to my app and that page will have product information. I was also able to redirect to the page and show the information on that page. I want to put the name of the product in the title value of the SliverAppBar. The product name is written in the productName variable.

But I can't enter a variable in the SliverAppBar's title value. When trying to login I get this error:

Evaluation of this constant expression throws an exception.dart(const_eval_throws_exception)

A value of type 'Null' can't be assigned to a parameter of type 'String' in a const constructor.
Try using a subtype, or removing the keyword 'const'.dartconst_constructor_param_type_mismatch

Avoid using braces in interpolation when not needed.dartunnecessary_brace_in_string_interps

Invalid constant value.

Codes:

child: CustomScrollView(
  slivers: <Widget>[
    const SliverAppBar(
      pinned: true,
      expandedHeight: 250.0,
      flexibleSpace: FlexibleSpaceBar(
        title: Text("Product ${productName}"),
      ),
    ),
  // ...

How can I solve this problem? Thanks in advance for your help.

CodePudding user response：

Just remove the const keyword in front of SliverAppBar widget

 SliverAppBar(
      pinned: true,
      expandedHeight: 250.0,
      flexibleSpace: FlexibleSpaceBar(
        title: Text("Product ${productName}"),
      ),
    ),