Parsing double to String is not accepted in function

Question

I need to convert a double variable to string to upload it as part of a http post request to the server:

  final response = await http.post(Uri.parse(url), body: {
      "fecha_inicio": _fechaInicioBBDD,
      "fecha_fin": _fechaFinalBBDD,
      "latitud": _controllerLatitud.text,
      "longitud": _controllerLongitud.text,
      "calle": _controllerDireccion.text,
      "descripcion": _controllerDescripcion.text,
      "tipo_aviso": tipoAviso,
      "activar_x_antes": double.parse(_horas.toString())

    });

The parameter "activar_x_antes": double.parse(_horas.toString()) is throwing an exception when executing the app:

Unhandled Exception: type 'double' is not a subtype of type 'String' in type cast

The value for _horas = 4.0

MendelG · Accepted Answer · 2022-03-08 16:43:48Z

4

When you are doing:

double.parse(_horas.toString())

this is converting _horas to a String and then again to a double. Instead, only call toString():

"activar_x_antes": _horas.toString()

answered Mar 8, 2022 at 16:43

MendelG

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1 Comment

Gustavo Rodrigues Over a year ago

Just an important note: if you need to reduce the size of the output, you should use .toStringAsFixed(int fractionDigits) or toStringAsExponential([int? fractionDigits]) like described in the docs here api.dart.dev/stable/2.16.1/dart-core/…

Majid · Accepted Answer · 2022-03-08 16:49:23Z

2

Let's take a closer look at why this is happening.

You have value _horas = 4.0; which is a double, you are trying to convert it to String to send it to the server. However, you are using double. parse.

Let's look at the parse doc. it says "Parse source as a double literal and return its value." in fact, you are parsing a number String back to double again!

What you can do is either

"activar_x_antes": _horas.toString()

or

"activar_x_antes": '$_horas'

I hope the explanation helps.

edited Mar 8, 2022 at 16:49

answered Mar 8, 2022 at 16:48

Majid

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3 Comments

MendelG Over a year ago

How is this any different to any of the answers provided below?

Majid Over a year ago

haha, I was type didn't notice three are other answers, that happens! sorry.

MendelG Over a year ago

ha, np. You did still provide an alternative of using string interpolation.

winfred adrah · Accepted Answer · 2022-03-08 16:41:57Z

1

Use

 final response = await http.post(Uri.parse(url), body: {
      "fecha_inicio": _fechaInicioBBDD,
      "fecha_fin": _fechaFinalBBDD,
      "latitud": _controllerLatitud.text,
      "longitud": _controllerLongitud.text,
      "calle": _controllerDireccion.text,
      "descripcion": _controllerDescripcion.text,
      "tipo_aviso": tipoAviso,
      "activar_x_antes": _horas.toString()

    });

_horas.toString()

answered Mar 8, 2022 at 16:41

winfred adrah

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Comments

jamesdlin · Accepted Answer · 2022-03-08 17:38:20Z

1

The documentation for http.post states:

body sets the body of the request. It can be a String, a List<int> or a Map<String, String>.

Since you are passing a Map, all keys and values in your Map are required to be Strings. You should not be converting a String to a double as one of the Map values.

answered Mar 8, 2022 at 17:38

jamesdlin

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