Swing Hacks

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Chapter 10, Audio

#78 Provide Audio Controls During Playback

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units represented by the control (like “dB” for a gain-related control, or

“frames per second” for one that is timing-related).

Anyways, you’ve probably figured out that you can build a GUI by using

Swing to provide a view to these

Control

s. In fact, it’s fairly straightforward

to take a factory approach to handing out

JComponent

s based on

Control

s, as

shown in Table 10-1.

The

CompoundControl can’t be handled as easily because you can’t know how

far you’ll have to recursively dig into its hierarchy of controls, nor how to

represent them in relation to one another. For what it’s worth, JavaSound

does not define any

CompoundControl.Type constants, and it’s not clear that

any

CompoundControls exist in J2SE; the Javadoc only speaks in theory of

supporting something like a graphic equalizer, which would need to be a

CompoundControl.

Theory to Practice

To handle the different types of controls that can be encountered, one nice

approach would be to build a factory: you hand it a

Control, and it gives you

back a

JComponent that you can add to your GUI. Example 10-12 shows a

simple implementation of this.

Table 10-1. Controls and their Swing representation

Control type Swing representation

BooleanControl JCheckBox

EnumControl JComboBox

FloatControl JSlider

Example 10-12. Factory to generate Swing widgets for JavaSound controls

import javax.sound.sampled.*;

public class ControlComponentFactory {

private ControlComponentFactory() {super( );}

public static JComponent getComponentFor (Control control) {

System.out.println (control.getType().getClass( ));

if (control instanceof BooleanControl)

return new BooleanControlComponent ((BooleanControl) control);

else if (control instanceof FloatControl)

return new FloatControlComponent ((FloatControl) control);

return new JLabel ("unsupported");

}

}

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Chapter 10, Audio

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You might notice that I haven’t written a GUI class for EnumControl. That’s

because in my testing, the array of

Controls returned by getControl( ) has

never contained an

EnumControl

, so I don’t have a good way to test it. After

looking at the implementation of the

boolean

and

float

cases, I’ll discuss

how an

EnumControlComponent

would work.

The easier case is the

BooleanControl

, used for controls like Mute, which

turns off the sound (but remembers the previous volume, so when un-

muted, the sound is as loud as it was before). Example 10-13 shows the

implementation of the

BooleanControlComponent

.

As you can see, this is practically trivial. The GUI contains a single

JCheckBox, whose value you set to the value of the control so that it is in a

proper state when first shown. Then, when the user clicks it, you just call

the

BooleanControl’s setValue( ) method.

Supporting a

FloatControl is a lot harder. As you might expect, the way to

represent a range of floating-point values is with a

JSlider; the user can slide

left to reduce the value and right to increase it. To ensure the GUI’s useful-

ness, you can put

JLabels on the left and right of the slider to show what the

minimum and maximum values mean. For example, on a Pan control,

which adjusts placement of stereo sound, the minimum value of -1.0 is Left

and the maximum value of 1.0 is Right.

What makes it hard is handling a mapping of arbitrary floating-point values to

a

JSlider’s int-based range. Complicating things is the fact that FloatControls

can and do use very different ranges for their values, often spanning nega-

tive and positive values, and operating in both small and vast ranges of

Example 10-13. Swing widget for a JavaSound BooleanControl

import javax.sound.sampled.*;

public class BooleanControlComponent extends JPanel

implements ActionListener {

BooleanControl control;

JCheckBox box;

public BooleanControlComponent (BooleanControl c) {

control = c;

box = new JCheckBox ( );

box.setSelected (control.getValue( ));

add (box);

box.addActionListener (this);

}

public void actionPerformed (ActionEvent ae) {

control.setValue (box.isSelected( ));

}

}