如果 class 没有上下文，如何从 Provider 获取数据？

Question

I am using Provider as state manager. I have few widgets that collect data. One of my widget is button that should to complete saving of all data. It have onPressed () {... } event. I would like to do some computation of data before saving.

I thought to do it in separate class:

class ResultProcessing 
{
    // here I need access to data from provider
}

Button:

  Flexible(
    child: Container(
       child: RaisedButton(
       child: Text("Save"),
       onPressed: () {
       // I need to pass data to ResultProcessing 
       },
     )),
   ),

But the problem that I can't get access to data in Provider , because ResultProcessing class is not widget and have not context .

The class name data from which I need to grab from my processing class is Provider.of<AppState>(context).customer;

And in which moment I should to create instance of ResultProcessing ? In onPressed event?

Answer 1

You don't, that's anti pattern. Your objects are purposefully not accessible outside of the widget tree.

You should change your approach. Instead, use widgets to act like a bridge between your model and your providers.

A typical example is ProxyProvider and similar variants

Answer 2

You can do something like this.

Flexible(
  child: Container(
   child: RaisedButton(
     child: Text("Save"),
     onPressed: () {
       DataClass data = Provider.of<DataClass>(context); 
       // Pass data to ResultProcessing
       ResultProcessing.handle(data);
     },
   ),
  ),
),

Answer 3

I solved it on a simple way. Add a required parameter to your class with a constructor and use it in the class, and then, send data from the widget where you have a build method(context) and access to the Provider.

class ResultProcessing {
    String data; // add a parameter
    ResultProcessing({required this.data}); // add the constructor
    {
        //use the data here as you want
    }
}