From Xojo Documentation
|You are currently browsing the old Xojo documentation site. Please visit the new Xojo documentation site!|
New in 2021r3
DesktopUIControl is the base class for most other visual control classes.
|DragActionCopy||Copy the dragged item.|
|DragActionMove||Move the dragged item.|
|DragActionLink||Link the dragged item.|
Most visual controls inherit the properties of the DesktopUIControl. A DesktopUIControl cannot be created or modified directly. Instead, you create and modify the DesktopUIControl subclasses like DesktopButtons, DesktopTextFields, DesktkopListBoxes, etc.
The Control Hierarchy
In some cases you build portions of your interface by placing some controls within another control. For example, you use the GroupBox control to organize other controls, usually RadioGroup or possibly CheckBoxes. The TabPanel and PagePanel controls also designed to enclose other controls.
The control that encloses the others is known as the parent control and the controls that are entirely within its borders are the child controls. This works automatically if you create the controls in the order of: parent-child. That is, create the control that encloses the others first, then create the child controls or duplicate existing child controls and keep them inside the parent control.
You can use the Parent property of the DesktopUIControl class to either get or set the parent of an existing control. If you create a child control before its parent, you can set its parent using its Parent property.
If a control is not completely enclosed by another control then it doesn't automatically become a child; it overlaps the other control.
If you move a child outside its parent, it is no longer a child of that control. If you move it completely inside another control, it becomes the child of that control.
When you copy a parent control, you copy all its child controls as well.
You can create more than one level of nesting. For example, you can place a GroupBox within a TabPanel and then place a RadioGroup within the GroupBox. In this case, the GroupBox is the parent of the RadioGroup and the TabPanel is the parent of the GroupBox. To make this work automatically, you must create them in the order that respects the hierarchy: first create the TabPanel, then the GroupBox, and then the RadioGroup.
Obviously, the parent control must be in the same window as its child controls. If you attempt to get the parent of a control whose parent is in another window, you will get an InvalidParentException error.
If a control is not enclosed by another control, then its “parent” is its window.
Control Hierarchy Features
To take advantage of the features of the control hierarchy automatically, create the parent control first and then add the child controls by dragging fully into the interior of the parent control. When you add a child to a parent in this manner, a marquee surrounds the parent. A marquee also surrounds the parent control whenever you select an existing child control. You can disable the marquee in Preferences/Options.
If you duplicate a child control and leave the duplicate within the parent, then it is automatically a child. However, if you move the duplicate outside the parent, it is no longer a child. A control must be fully enclosed by the parent to be considered a child.
When you move a child out of the 'scope' of the parent, the marquee surrounding the parent is turned off, indicating that the child is not under parental control anymore.
- Deleting a parent control deletes all child controls.
- Hiding a parent hides all child controls, but retains the previous visibility status of all children.
- Showing a parent control shows only the child controls whose visibility is set.
- Disabling a parent control disables all its child controls, but retains the previous visibility status of all children. In the IDE, disabling a container visually disables all the child controls, but does not update the Enabled property.
- Disabling the TabPanel disables all child controls, as expected.
There are three possible items a user can drag from a control: text, a picture, and/or a FolderItem. In order for the user to be able to drag, the control must create a DragItem object in the appropriate event handler. The appropriate event handler depends on the type of object. For example, the appropriate event handler for a DesktopCanvas control is the MouseDown event handler since the user must be holding down the mouse button to drag.
The DragItem object represents the data that the user is dragging. DragItem objects have properties to hold text, pictures, and folderItems. One or more of these properties must be populated with the values the user wishes to drag. When you create a new DragItem object using the DragItem constructor, you specify the drag rectangle that will appear as the user drags from the control.
TextFields, TextAreas, and ListBoxes have implicit dragging built in to them. This means that they will create a new DragItem and drag rectangle for you. TextFields and TextAreas automatically populate the Text property of the DragItem with the text the user is dragging. ListBoxes have a DragRow event handler where you can populate the DragItem with the data to be dragged.
Before a control will accept an item being dropped on it, you must call the AcceptFileDrop, AcceptPictureDrop, AcceptRawDataDrop, and/or AcceptTextDrop methods to indicate the drop types that will be allowed. This is usually done in the control's Opening event handler. When an acceptable item is dropped on the control, the control's DropObject event handler will execute and will be passed the DragItem that has been dropped on the control. At that point you can use the DragItem's methods to determine what kind of data is available and access it. If you are only allowing a particular type of drag data (text for example) then there would be no need to test the type of data that is being dragged. You can get the text from the Text property of the DragItem.
Handling Contextual Menus
Return True //display the contextual menu
MessageBox("You chose Import")
MessageBox("You chose export")
On macOS, standard controls no longer filter contextual clicks. This responsibility can always be overridden by you in the MouseDown event for the control.
Changing the Cursor
The MouseCursor property controls which cursor will be displayed while the mouse is within the control, assuming that the MouseCursor properties of the DesktopApplication and parent DesktopWindow classes are Nil. You can, for example, assign different MouseCursors to different controls within a window and the shape of the pointer will change whenever it is over a particular control. The Cursors module contains a library of custom cursors that you access with the syntax System. Cursors.MouseCursorName. Please see the MouseCursor class for information about the library of custom cursors.
If you also need custom cursors at the Window or Application levels, you need to manage them along the lines described in the section on the MouseCursor class.
Custom Cursors in Windows
If you need to use custom cursors in the Windows build of your application, you can do so using a slightly modified version of this technique.
1. With a resource editor, create a CURS resource that contains only one cursor. Give the resource file a name that indicates the type of cursor contained in the resource file.
2. Repeat this process for each custom cursor. 3. Add all the resource files to the Project Editor. 4. You can then access each custom cursor by name, e.g.
This example shows how the DropObject event handler of a DesktopTextArea (named TextArea1 in this example) would be coded to handle one or more text documents or some text being dropped on it:
If Obj.TextAvailable Then
TextArea1.Text = Obj.Text
ElseIf Obj.FolderItemAvailable Then
// Load the styled text from the document
// into TextArea1
If Not TextArea1.Open(Obj.FolderItem) Then
Loop Until Not Obj.NextItem