Initializing Bound Controls

OpenOffice.org Developer's Guide

Forms

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• Models and Views

• The Model-View Paradigm
• Models and Views for Form Controls
• Model-View Interaction
• Form Layer Views

• Form Elements in the Document Model

• A Hierarchy of Models

• FormComponent Service
• FormComponents Service
• Logical Forms
• Forms Container
• Form Control Models

• Control Models and Shapes

• Form Components

• Control Models
• Forms
• HTML Forms

• Data Awareness

• Forms

• Forms as Row Sets
• Loadable Forms
• Sub Forms
• Filtering and Sorting
• Parameters

• Data Aware Controls

• Control Models as Bound Components
• Committing Controls

• External Value Suppliers

• Value Bindings

• Form Controls accepting Value Bindings

• External List Sources

• Validation

• Validation in OpenOffice.org
• Validation and Bindings

• Scripting and Events
• Common Tasks

• Initializing Bound Controls
• Automatic Key Generation
• Data Validation
• Programmatic Assignment of Scripts to Events

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All form controls specify a default value that is used when initially displaying the control, and when it is reset. For instance, resetting (com.sun.star.form.XReset) happens when a form is moved to the insert row, that allows data to be inserted as a new row into the underlying row set.

Now, you do not want a fixed default value for new records, but a dynamically generated one that is dependent on the actual context at the moment the new record is entered.

Or, you want to have real null values for date fields. This is currently not possible, because the com.sun.star.form.component.DateField service interprets a null default as an instruction to use the current system date. Effectively, you cannot have date fields in forms which default to null on new records, but you can get this by programming the API.

  public void handleReset(EventObject aEvent) throws com.sun.star.uno.RuntimeException {
      if (((Boolean)xFormProps.getPropertyValue("IsNew")).booleanValue()) {
          // the form is positioned on the insert row
 
          Object aModifiedFlag = xFormProps.getPropertyValue("IsModified");
 
          // get the columns of the form
          XColumnsSupplier xSuppCols = (XColumnsSupplier)UnoRuntime.queryInterface(
              XColumnsSupplier.class, xFormProps);
          XNameAccess xCols = xSuppCols.getColumns();
 
          // and update the date column with a NULL value
          XColumnUpdate xDateColumn = (XColumnUpdate)UnoRuntime.queryInterface(
              XColumnUpdate.class, xCols.getByName("SALEDATE"));
          xDateColumn.updateNull();
 
          // then restore the flag
          xFormProps.setPropertyValue("IsModified", aModifiedFlag);
      }
  }

The first decision is where to step in. We chose to add a reset-listener to the form, so that the form is reset as soon as it has been positioned on the new record. The resetted() method is called after the positioning is done.

However, resets also occur for various reasons therefore check if the form is really positioned on the insert row, indicated by the IsNew property being true.

Now besides retrieving and updating the data column with the desired value, null, there is another obstacle. When the form is moved to the insert row, and some values are initialized, the row should not be modified. This is because a modified row is saved in the database, and we only initialized the new row with the defaults, the user did not enter data. We do not want to store the row, therefore we save and restore the IsModified flag on the form while doing the update.

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