This is my code.( A detail page for json api response) I'm trying to make color red if negative, and green if positive. My code is :

class StocksDetailScreen extends StatefulWidget {


  final String? degisimoran;
  final String? sondeger;
  final String? hacim;
  final String? mindeger;
  final String? maxdeger;
  final String? hisseismi;
  final String? hissekodu;



  const StocksDetailScreen({
    Key? key,
    this.degisimoran,
     this.sondeger,
     this.hacim,
     this.mindeger,
     this.maxdeger,
     this.hisseismi,
     this.hissekodu,


  }) : super(key: key);

  @override
  State<StocksDetailScreen> createState() => _StocksDetailScreenState();
}

class _StocksDetailScreenState extends State<StocksDetailScreen> {
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text(widget.hisseismi!,style: TextStyle(fontSize: 18, fontWeight: FontWeight.w900),),

        ),
        body: SafeArea(
          bottom: true,
          top: false,
          maintainBottomViewPadding: true,
          child: Column(
            children: [
              Expanded(
                child: CustomScrollView(
                  slivers: <Widget>[
                    SliverToBoxAdapter(
                      child: Column(
                        crossAxisAlignment: CrossAxisAlignment.start,
                        children: <Widget>[

                          Divider(height: 3.6,),
                          SizedBox(height: 50,),
                          Column(
                              mainAxisAlignment: MainAxisAlignment.end,
                              children: <Widget>[
                                FadeInUp(
                                  duration: Duration(milliseconds: 1000),
                                  from: 30,
                                  child: Text(
                                    widget.sondeger!,
                                    style: GoogleFonts.poppins(
                                      textStyle: TextStyle(
                                        color: widget.sondeger! > 0
                                        ? Colors.green
                                        : Colors.red,
                                        fontSize: 36,
                                        fontWeight: FontWeight.bold,
                                      ),
                                    ),
                                  ),
                                ),
...

On the line:

                                  child: Text(
                                    widget.sondeger!,
                                    style: GoogleFonts.poppins(
                                      textStyle: TextStyle(
                                        color: widget.sondeger! > 0
                                        ? Colors.green
                                        : Colors.red,
                                        fontSize: 36,
                                        fontWeight: FontWeight.bold,
                                      ),
                                    ),
                                  ),

I get this error. error: The operator '>' isn't defined for the type 'String'. dart flutter. How can i fix this? Thanks for your help

CodePudding user response：

Hi your variable is a string and in dart you can't do it. Before that you need convert string to integer.

final String? sondeger;

In dart you can convert like that.

int.parse(sondeger)>0

But this variable is nullable and if you are not sure about this variable can be not number. I suggest you to use

int.tryParse(var);

More information

CodePudding user response：

You have the variable sondeger defined as String?.

So, you have to parse the String variable into int and compare it.

Example

child: Text(
   widget.sondeger!,
   style: GoogleFonts.poppins(
   textStyle: TextStyle(
         color: (int.tryParse("${widget.sondeger}") ?? 0) > 0
                 ? Colors.green
                  : Colors.red,
         fontSize: 36,
          fontWeight: FontWeight.bold,
       ),
     ),
 ),

It tries to parse the given string into int; if failed, defaults to 0.

CodePudding user response：

You are using final String? sondeger; as String, it cant have smaller or greater condition like this. You may int as parameter to access the pass number.

  final int? sondeger;

Text(
  "${widget.sondeger}",
  style: GoogleFonts.poppins(
    textStyle: TextStyle(
      color: (widget.sondeger??0) > 0 ? Colors.green : Colors.red,
      fontSize: 36,
      fontWeight: FontWeight.bold,
    ),
  ),
);

To receive string follow selimdogan