Using the JProgressBar Control

How to customize the appearance of a JProgressBar control.

About this technique	Details
Category	Java Client Techniques> Version 3 Swing-based controls
Description	You'll learn about: Specifying the control's size and position Selecting colors Using the timer Responding to changes in the progress bar's value
	You can run this technique code from: Database: Examples3_Java Form: frmJProgressMeter NOTE   First make sure that database is running on your localhost SilverStream Server
Related reading	For another example of: Overriding addControls(), see Implementing a Nested Layout Using the timer, see Using Timers Adding listeners, see Adding a Listener to a Form Control

JProgressBar is part of the JDK and is not extended by SilverStream. In the Form Designer, it is on the Other toolbar. The example frmJProgressMeter has a timer that "ticks" every .3 seconds and increments the value of the progress bar by 5 on each tick. The form also has several controls that let the user change the appearance of the progress bar as well as start and stop the timer.

Specifying the control's size and position   

In frmJProgressMeter, the user can choose a vertical or horizontal progress bar. During initialization, code in the formActivate event saves the initial position and size of the horizontal progress bar in instance variables.

  // Get the JProgress bar location and size 
  Point point = jProgressBar.getLocation(); 
  m_xPosition = point.x; 
  m_yPosition = point.y; 
   
  Dimension dimension = jProgressBar.getSize(); 
  m_horizontalWidth = dimension.width; 
  m_horizontalHeight = dimension.height; 
   
   

When the user selects vertical orientation, the code for the button's actionPerformed event changes the orientation. It also changes the width and height to a tall, thin shape.

  private void handle_rbVertical_actionPerformed(ActionEvent evt) 
  { 
     jProgressBar.setOrientation (JProgressBar.VERTICAL); 
     jProgressBar.setBounds (m_xPosition, m_yPosition, 
        m_verticalWidth, m_verticalHeight); 
  } 

Notes on the code

• Values for the width and height when the control is vertical are specified in instance variables.

    int m_verticalWidth = 40; 
    int m_verticalHeight = 320; 
  

Selecting colors   

Two image buttons let the user choose a background and foreground color for the progress bar. The code for the background button's actionPerformed event uses the JDK's color selection dialog box.

  private void handle_imgBackgroundColor_actionPerformed(ActionEvent evt) 
  { 
     Color colorBack = JColorChooser.showDialog (getParent(), 
        "Progress Bar Background", jProgressBar.getBackground()); 
     jProgressBar.setBackground (colorBack); 
  } 

Using the timer   

The user starts and stops the timer via buttons on the form. The timer has not been set to start automatically. This code starts and stops the timer.

  private void handle_imgStart_actionPerformed(ActionEvent evt) 
  { 
     jProgressBar.setValue (0); 
     tmrProgressBar.startTimer(); 
  } 
  private void handle_imgStop_actionPerformed(ActionEvent evt) 
  { 
     tmrProgressBar.stopTimer(); 
  } 

This code updates the progress bar after each timer interval.

  private void handle_tmrProgressBar_timeIntervalExpired(EventObject event) 
  { 
     jProgressBar.setValue (jProgressBar.getValue() + 5); 
     if (jProgressBar.getValue() >= 100) jProgressBar.setValue (0); 
  } 

Responding to changes in the progress bar's value   

The stateChanged event for the progress bar is fired when the value of the progress bar changes. It is not automatically available in the Form Designer. There are three parts to using it in this example:

• Imports the javax.swing.event package

    import javax.swing.event.*; 
  

• Adds the form as a ChangeListener for the progress bar

    public void addControls() 
    { 
       // Add all the form designer defined controls 
       super.addControls (); 
       jProgressBar.addChangeListener(this);  
    } 
  

• Displays the progress bar's current value in a label control

    public void stateChanged (ChangeEvent evt) 
    { 
    JProgressBar jprogressBar = (JProgressBar)evt.getSource(); 
    lblDisplayProgress.setText("Current Progress Bar Value: " + 
       jprogressBar.getValue()); 
    } 
  

Notes on the code

• addControls() in AgfForm calls addAllFormControls(), code generated by SilverStream that adds to the form all the controls you specified in the Designer plus listeners for their events. This form overrides addControls() to add ChangeListener but calls super.addControls() to add the controls.

• In stateChanged, getSource() gets the control that generated the event, which is cast to JProgressBar.