Data API

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## Managing data in a screen

For managing the data of a screen, the CustomScreen provides a simple API which can be accessed via getDataApi('DATA_PROVIDER_NAME') from anywhere in it's extended classes.

This API provides the following functions:

- dynamic getValue(String columnName) - Provides the value of a specific column - List getValues(List columnNames) - Provides a list of values for the specified columns - setValue(String columnName, dynamic value) - Sets the value for a specific column - setValues(List columnNames, List values) - Sets the values for a list of specified columns - insertRecord() - Inserts a new record - deleteRecord(int index) - Deletes the record at the specified index - selectRecord(int index) - Selects the record at the specified index

The client persists those changes by itself.

## Examples Reading a value:

  DataApi dataApi = getDataApi('JVxMobileDemo/Con-CG/contacts#4');
  
  FlatButton(
    child: Text("Call"), onPressed: () {
    phone = dataApi.getValue("PHONE");
    launch("tel://$phone");
  })

Setting a value:

  DataApi dataApi = getDataApi('JVxMobileDemo/Con-CG/contacts#4');
  dynamic phoneNr = '+43660123456'
  
  FlatButton(
    child: Text("Set phone number"), onPressed: () {
    phone = dataApi.setValue("PHONE", phoneNr);
  })
 
 Inserting a record:

  DataApi dataApi = getDataApi('JVxMobileDemo/Con-CG/contacts#4');
  
  FlatButton(
    child: Text("Insert"), onPressed: () {
    phone = dataApi.insertRecord();
  })

More examples can be found [here](https://github.com/sibvisions/flutterclient.example/blob/master/lib/screens/signature_custom_screen.dart) and [here](https://github.com/sibvisions/flutterclient.example/blob/master/lib/screens/contact_custom_screen.dart).