Implementation

Button

The Button class extends CanvasGraphicsItem and defines both the controls and appearance of a button. The Button class shows you how to use the CanvasGraphicsItem class to encapsulate a simple Canvas graphics control.

The Button class handles pointer events for changing between normal (pointerReleased) and pressed (pointerPressed) states. It executes the "click" event handler passed through its constructor when the button is released. The button can also be disabled.

CanvasTextBox

The CanvasTextBox class implements a control with a label, text editing area, and keyboard indicator. The class extends CanvasGraphicsItem, on which the label and text editing area borders are drawn. Text editing is provided by a TextEditor object.

On Series 40 touch devices, controls for moving the caret and clearing characters are drawn above the TextEditor object.

On Symbian devices, if the TextEditor is constructed as a multiline field, a simple scroll bar is displayed.

A CanvasTextBox object can be in normal, focused, or disabled state.

Caret controls

Series 40 touch and type devices do not support a virtual keyboard for editing text, so the Controls class implements the following caret controls for TextEditor to ensure its usability:

• Erasing a character:

  int caretPosition = owner.getCaretPosition();
  if (caretPosition > 0) {
      owner.delete(caretPosition - 1, 1);
      owner.setCaret(caretPosition - 1);
  }

• Moving the caret to the left:

  int caretPosition = owner.getCaretPosition();
  if (caretPosition > 0) {
      owner.setCaret(caretPosition - 1);
  }

• Moving the caret to the right:

  int caretPosition = owner.getCaretPosition();
  if (caretPosition < owner.size()) {
      owner.setCaret(caretPosition + 1);
  }

Figure: Caret controls for a TextEditor on a Series 40 full touch device

Scroll bar

On Symbian devices, a TextEditor supports the use of scroll bars through the following methods:

• TextEditor.getHeight (inherited from CanvasItem)

• TextEditor.getContentHeight

• TextEditor.getVisibleContentPosition

Figure: Scroll bar in a TextEditor on a Symbian device

On Series 40 devices, using scroll bars is not supported, since the getVisibleContentPosition method always returns 0, which means the position of the scroll bar cannot be known, and the setCaretXY method is not supported.