Class WAbstractItemDelegate

Direct Known Subclasses:

public abstract class WAbstractItemDelegate extends WObject
Abstract delegate class for rendering an item in an item view.

Rendering of an item in a WAbstractItemView is delegated to an implementation of this delegate class. The default implementation used by JWt's item views is WItemDelegate. To provide specialized rendering support, you can reimplement this class (or specialize WItemDelegate).

As a delegate is used for rendering multiple items, the class should not keep state about one specific item.

A delegate may provide editing support by instantiating an editor when update() is called with the ViewItemRenderFlag.Editing flag. In that case, you will also need to implement getEditState() and setEditState() to support virtual scrolling and setModelData() to save the edited value to the model. For an example, see the WItemDelegate.

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  • Constructor Details

    • WAbstractItemDelegate

      public WAbstractItemDelegate()
  • Method Details

    • update

      public abstract WWidget update(WWidget widget, WModelIndex index, EnumSet<ViewItemRenderFlag> flags)
      Creates or updates a widget that renders an item.

      The item is specified by its model index, which also indicates the model. If an existing widget already renders the item, but needs to be updated, it is passed as the widget parameter.

      When widget is null, a new widget needs to be created and returned.

      If you want to replace the widget with a new one, return the new widget. The old widget will be removed. Return null if you do not want to replace the widget.

      You can remove the widget from its parent for reuse with WWidget.removeFromParent().

      The returned widget should be a widget that responds properly to be given a height, width and style class. In practice, that means it cannot have a border or margin, and thus cannot be a WFormWidget since those widgets typically have built-in borders and margins. If you want to return a form widget (for editing the item), you should wrap it in a container widget.

      The flags parameter indicates options for rendering the item.

    • update

      public final WWidget update(WWidget widget, WModelIndex index, ViewItemRenderFlag flag, ViewItemRenderFlag... flags)
      Creates or updates a widget that renders an item.

      Returns update(widget, index, EnumSet.of(flag, flags))

    • updateModelIndex

      public void updateModelIndex(WWidget widget, WModelIndex index)
      Updates the model index of a widget.

      This method is invoked by the view when due to row/column insertions or removals, the index has shifted.

      You should reimplement this method only if you are storing the model index in the widget, to update the stored model index.

      The default implementation does nothing.

    • getEditState

      public Object getEditState(WWidget widget, WModelIndex index)
      Returns the current edit state.

      Because a View may support virtual scrolling in combination with editing, it may happen that the view decides to delete the editor widget while the user is editing. To allow to reconstruct the editor in its original state, the View will therefore ask for the editor to serialize its state in a boost::any.

      When the view decides to close an editor and save its value back to the model, he will first call getEditState() and then setModelData().

      The default implementation assumes a read-only delegate, and returns a boost::any().

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    • setEditState

      public void setEditState(WWidget widget, WModelIndex index, Object value)
      Sets the editor data from the editor state.

      When the View scrolls back into view an item that was being edited, he will use setEditState() to allow the editor to restore its current editor state.

      The default implementation assumes a read-only delegate and does nothing.

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    • validate

      public ValidationState validate(WModelIndex index, Object editState)
      Returns whether the edited value is valid.

      The default implementation does nothing and returns Valid.

      See Also:
    • setModelData

      public void setModelData(Object editState, WAbstractItemModel model, WModelIndex index)
      Saves the edited data to the model.

      The View will use this method to save the edited value to the model. The editState is first fetched from the editor using getEditState().

      The default implementation assumes a read-only delegate does nothing.

    • closeEditor

      public Signal2<WWidget,Boolean> closeEditor()
      Signal which indicates that an editor needs to be closed.

      The delegate should emit this signal when it decides for itself that it should be closed (e.g. because the user confirmed the edited value or cancelled the editing). The View will then rerender the item if needed.

      The second boolean argument passed to the signal is a flag which indicates whether the editor feels that the value should be saved or cancelled.

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