Unable to get TEdit to connect with dataset under Livebindings when setting datasource.dataset at runtime

Question

How do I get controls other than TStringGrid to work properly with Livebindings when the Dataset property of their Datasource is set at runtime? I am able get a TStringGrid to recognize the dataset fields, but not other controls such as TEdit.

Here are details of my project. I have created a datamodule and a form. The datamodule which has the dataset objects and the form has a datasource along with UI controls. To reduce dependencies between modules, I do not want the form unit to use the datamodule unit. Rather, I want to set the datasource.dataset at runtime. If I use a TStringGrid, this strategy works, but with TEdit, it does not. I have tried manually creating the fields in LiveBindings, but these do not map to the dataset. If I were using VCL, this would be a non-issue, but I have been unable to figure out the best way to accomplish this with Livebindings. FYI, this is a FMX project.

I also noticed that if I "used" the datamodule to create the Livebinding connections and subsequently unused it, the fields show up on the BindSourceDb and read (invalid). When I run the application and set the dataset property at runtime, the TEdit controls are able to find the fields an will work fine. Any suggestions how to do this without using and using modules?

By "use" I mean I add the file to one of the uses section and "unuse" means I removed it. — Terry Thompson
By "use" I mean I add the file to the uses section under implementation and "unuse" means I removed it. I am programming to interfaces. The form has an interface property called ViewModel which I set immediately after the form is created. In the ViewModel set procedure, there is code which reads Datasource.Dataset := ViewModel.Dataset. The Datasource is already attached to a BindSourceDb. If I were doing this with a data aware application, all of the controls attached to the datasource would automatically connect and populate with data. How do I make this work with Livebindings? — Terry Thompson

MartynA MartynA · Accepted Answer · 2016-09-25T17:13:29

The following project works fine for me using LiveBindings. I did what I understood you to be describing, namely

The Form unit, DynLiveBindingsu, initally Used the datamodule unit DynDMu. In that condition, I added the live bindings components to the form and "wired them up", starting by populating a BindingList object, and then using it to add a TLinkGridToDataSource and TLinkControlToField and setting their properties.
Then, I removed the reference to DynDMu from the form's Uses list, compiled and ran the project and the StringList1 and Edit1 are correctly bound to the dataset in the datamodule.

Obviously I can't see your project so have no idea why you are getting a problem, but at least this answer gives you a working project to use as the basis of a comparison with yours.

Notice, btw, that there is no TDataSource involved, either in the datamodule or the form.

I'm using Delphi Seattle, btw.

DataModule:

unit DynDMu;
[...]
type
  TDataModule1 = class(TDataModule)
    CDS1: TClientDataSet;
    CDS1Name: TStringField;
    CDS1ID: TIntegerField;
    procedure DataModuleCreate(Sender: TObject);
  end;

[...]

procedure TDataModule1.DataModuleCreate(Sender: TObject);
begin
  CDS1.CreateDataSet;
  CDS1.InsertRecord([1, 'One']);
  CDS1.InsertRecord([2, 'Two']);
  CDS1.InsertRecord([3, 'Three']);
end;

Form unit

unit DynLiveBindingsu;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Data.Bind.EngExt,
  Vcl.Bind.DBEngExt, Vcl.Bind.Grid, System.Rtti, System.Bindings.Outputs,
  Vcl.Bind.Editors, Data.Bind.Components, Data.Bind.DBScope, Data.Bind.Grid,
  Data.DB, Vcl.StdCtrls, Vcl.Grids, Data.Bind.Controls, Vcl.ExtCtrls,
  Vcl.Buttons, Vcl.Bind.Navigator;

type
  TForm1 = class(TForm)
    StringGrid1: TStringGrid;
    Edit1: TEdit;
    BindingsList1: TBindingsList;
    LinkGridToDataSource1: TLinkGridToDataSource;
    BindSourceDB1: TBindSourceDB;
    BindNavigator1: TBindNavigator;
    LinkControlToField1: TLinkControlToField;
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

end.

Form DFM

object Form1: TForm1
[...]
  object StringGrid1: TStringGrid
  [...]
  end
  object Edit1: TEdit
  [...]
  end
  object BindNavigator1: TBindNavigator
    Left = 16
    Top = 150
    Width = 240
    Height = 25
    DataSource = BindSourceDB1
    Orientation = orHorizontal
    TabOrder = 2
  end
  object BindingsList1: TBindingsList
    Methods = <>
    OutputConverters = <>
    Left = 216
    Top = 184
    object LinkGridToDataSource1: TLinkGridToDataSource
      Category = 'Quick Bindings'
      DataSource = BindSourceDB1
      GridControl = StringGrid1
      Columns = <
        item
          MemberName = 'ID'
        end
        item
          MemberName = 'Name'
        end>
    end
    object LinkControlToField1: TLinkControlToField
      Category = 'Quick Bindings'
      DataSource = BindSourceDB1
      FieldName = 'Name'
      Control = Edit1
      Track = False
    end
  end
  object BindSourceDB1: TBindSourceDB
    DataSet = DataModule1.CDS1
    ScopeMappings = <>
    Left = 296
    Top = 184
  end
end

Unable to get TEdit to connect with dataset under Livebindings when setting datasource.dataset at runtime

2 Answers