Dynamically Binding Controls to Data

How to create form controls at runtime and dynamically bind them to data.

About this technique	Details
Category	Data Access Techniques> General
Description	You'll learn about: Creating a control that accesses an independent data set Binding the property of a text field to a data source property Invoking the data source object
	You can run this technique code from: Database: Examples3_Java Form: frmDynamicBinding NOTE   First make sure that database is running on your localhost SilverStream Server
Related reading	See the chapter on data access basics in the Programmer's Guide

The example shows how you can dynamically create form fields and bind them to a data set through a data source object. When the form is activated, it displays those fields and the appropriate data from the data set.

Creating a control that accesses an independent data set   

The following code creates an AgcData object and specifies the data source object (DSO) that it references. The referenced DSO contains data that is independent of the rest of the form.

  // Code fragment in formActivate() 
   
  // Create an AgcData, referencing the Data Source Object, dsoEmployee 
     agcDynamic = new AgcData (); 
     agcDynamic.setName ("agcDynamic"); 
     agcDynamic.setDataSource ("dsoEmployee"); 
     this.add(agcDynamic, 0); 

Notes about the code

• Create the invisible control that access a specific data set.

• Set its name.

• Specify that instead of using a relational data table, this AgcData object should act as a proxy to the dsoEmployee data source business object.

• Add the control to this form.

Binding the property of a text field to a data source property   

The code creates a label and a text field on the form, then uses bind to bind the text field to a property of the specified data source object so that the text field dynamically displays the specified data. You specify the names of the control's "set" and "get" methods. These methods allow the application to get an edited field value and change its corresponding data source property value and the reverse.

  // Code fragment in formActivate() 
   
  // Create an Employee ID Label  
  // Create a field and bind it to the employeeid in agcData 
  AgcLabel idLabel = addLabel ("Employee ID", LABEL_LEFT, FIELD_TOP,  
     LABEL_WIDTH, LABEL_HEIGHT); 
  AgcTextField employeeidField = addTextField (TEXT_LEFT, FIELD_TOP,   
     TEXT_WIDTH, TEXT_HEIGHT); 
  agDataMgr.bind (employeeidField, "Text", "getText", "setText",  
     agcDynamic, new Integer(0) ); 

Notes about the code

• agDataMgr.bind() binds the "Text" property of the employeeidField control to the first property (as specified by index number 0) of the data source.

• The "get" method on the employeeidField control that retrieves its property value is "getText".

• The "set" method on the employeeidField control that sets the property value is "setText".

Invoking the data source object   

The following code shows how to invoke the data source object (or business object) for which this AgcData object is a proxy.

  // Code fragment in formActivate() 
   
  // Invoke the DSO 
  try 
  { 
     agcDynamic.invokeQuery(""); 
     agcDynamic.gotoFirst(); 
  } 
  catch (Exception e) 
  { 
     agDialog.displayError(e); 
  } 

Notes about the code

• Invoke the query that gets the first property of the referenced DSO, for all records. invokeQuery() initializes the datastore with the resulting data source.

• Position the cursor in the first record of the dataset by calling gotoFirst(). In this example, the first record is displayed in all the text fields.