Binding VCL Controls to a TClientDataSet with LiveBindings in RAD Studio

Problem

You want VCL controls such as TEdit or TLabel to show and update data from a TClientDataSet without writing manual DataSource.DataField assignments or event handlers.

Takeaway

By adding a TBindSourceDB component and using the LiveBindings Designer you can create bidirectional links that keep the dataset and the controls in sync automatically.

Prerequisites

• RAD Studio 10.4 Sydney or later (the LiveBindings design‑time package is included).
• A VCL Forms Application project.
• A TClientDataSet placed on a form or a TDataModule with some sample data loaded (e.g., via LoadFromFile or created at runtime).
• The VCL controls you wish to bind (e.g., TEdit, TLabel, TComboBox) already dropped on the form.

Procedure

1. Add the binding source
   1. Open the form in the Designer.
   2. From the Tool Palette, drag a TBindSourceDB component onto the form (or the DataModule).
   3. With the component selected, set its DataSet property to the TClientDataSet you want to bind.
   4. Optionally, set AutoActivate to true so the source becomes active when the form is created.
2. Open the LiveBindings Designer
   1. Select the form, then choose View → LiveBindings Designer from the main menu (or press Alt+Shift+L).
   2. The designer splits into two panels: left shows available sources (your TBindSourceDB), right shows bindable controls on the form.
3. Create the bindings
   1. In the left panel, expand the TBindSourceDB node to reveal its fields (e.g., Field1, Field2).
   2. Drag a field onto the target control you want to bind. For example, drag Field1 onto a TEdit.
   3. A dialog appears asking for the binding mode. Choose Edit for two‑way synchronization (control ↔ dataset) or Display for read‑only.
   4. Repeat for each control‑field pair you need.
4. Activate the bindings
   1. In the LiveBindings Designer toolbar, click the Activate All Bindings button (green lightning bolt).
   2. Active bindings appear as green links; inactive or broken links are red.
5. Run and verify
   1. Press F9 to compile and run the application.
   2. Navigate the dataset (if you have a TDBGrid or TNavigator) and observe that the bound controls update instantly to show the current record’s values.
   3. Edit the text in a bound TEdit and press Enter or move focus away; the change should be written back to the TClientDataSet.
   4. To confirm the dataset receives the edit, place a breakpoint on the TClientDataSet.OnAfterEdit event; it should fire after each control‑initiated change.

Expected Checks

• The LiveBindings Designer shows green links for every field‑control pair you created.
• Running the application yields immediate visual feedback: changing a record in the dataset updates the controls, and editing a control updates the dataset.
• No exceptions are raised when the form is created or when navigating the dataset.

Limitations

• LiveBindings require the RTL and FireMonkey packages; in a pure VCL project ensure the "LiveBindings" design‑time package is installed, otherwise the designer will be disabled.
• If you set the TClientDataSet.Active property to false at runtime (e.g., to reload data), the bindings become inactive. You must either set TBindSourceDB.Active := false then true after reactivating the dataset, or call Bindings.Reset to re‑establish the links.
• Complex expressions or custom converters are not covered by the basic drag‑and‑drop method; they require manual editing of the binding expressions in the LiveBindings Designer.

Recovery Options (Rollback)

If the bindings do not behave as expected:

1. Select the TBindSourceDB component and set its Active property to false.
2. In the LiveBindings Designer, select each red link and press Delete to remove it.
3. Delete the TBindSourceDB component from the form.
4. Re‑add a fresh TBindSourceDB and repeat the binding steps.
5. As an alternative, revert to the classic VCL approach: set each control’s DataSource to a TDataSource linked to the TClientDataSet and set the DataField property directly.

Practical Verification

After completing the steps, you can verify the setup on a clean RAD Studio installation by:

1. Exporting the project (File → Export → Export Project) to a zip file.
2. Extracting it on another machine with the same RAD Studio version.
3. Opening the project, compiling, and running it.
4. Confirming that the LiveBindings Designer still shows green links and that the UI‑dataset synchronization works as described.