| id | title | brief | article | sdk | |||||||||||||||
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B620BDFA-8377-4FD0-AC9E-7BB0D4289863 |
SeekBar |
This recipe demonstrates how to use the SeekBar control. The SeekBar control is visually similar to the ProgressBar but it has a draggable slider that will allow the user to change the value displayed by the control. This will provide an example showing how to respond to changes in the SeekBar using .NET events or the SeekBar.IOnSeekBarrChangeListenerinterface. |
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The SeekBar widget is an interactive slider that allows the user to select one value from a range of values. As the user moves the slider left or right, the value of the SeekBar will change. The following image shows an example of the SeekBar:
A SeekBar is added to the layout of an Activity or a Fragment. The following snippet is an example of the SeekBar XML:
<SeekBar android:layout_width="fill_parent" android:layout_height="wrap_content" android:id="@+id/seekBar1" android:layout_marginTop="@dimen/seekbar_margin" android:layout_marginBottom="@dimen/seekbar_margin"/>
Xamarin.Android provides some events that allow applications to respond to changes in the value of the SeekBar, the most significant of these is the ProgressChanged event.
This code snippet shows an example of attaching a lambda to the SeekBar.ProgressChanged event:
_seekBar = FindViewById<SeekBar>(Resource.Id.seekBar1);
_textView = FindViewById<TextView>(Resource.Id.textView1);
_seekBar.ProgressChanged += (object sender, SeekBar.ProgressChangedEventArgs e) => {
if (e.FromUser)
{
_textView.Text = string.Format("The value of the SeekBar is {0}", e.Progress);
}
};
This lambda will update a TextView widget with the value of the SeekBar when the change is triggered by the user. The following screen shot is an example of what an Activity might look like after the user has moved the slider:
As an alternative to using event handlers, classes that implement the interface SeekBar.IOnSeekBarChangeListener may act as listeners to the SeekBar events. The following code snippet shows an example of an Activity that implements SeekBar.IOnSeekBarChangeListener:
public class MainActivity : Activity, SeekBar.IOnSeekBarChangeListener
{
SeekBar _seekBar;
TextView _textView;
protected override void OnCreate(Bundle bundle)
{
base.OnCreate(bundle);
// Set our view from the "main" layout resource
SetContentView(Resource.Layout.Main);
_seekBar = FindViewById<SeekBar>(Resource.Id.seekBar1);
_textView = FindViewById<TextView>(Resource.Id.textView1);
// Assign this class as a listener for the SeekBar events
_seekBar.SetOnSeekBarChangeListener(this);
}
public void OnProgressChanged(SeekBar seekBar, int progress, bool fromUser)
{
if (fromUser)
{
_textView.Text = string.Format("The user adjusted the value of the SeekBar to {0}", seekBar.Progress);
}
}
public void OnStartTrackingTouch(SeekBar seekBar)
{
System.Diagnostics.Debug.WriteLine("Tracking changes.");
}
public void OnStopTrackingTouch(SeekBar seekBar)
{
System.Diagnostics.Debug.WriteLine("Stopped tracking changes.");
}
}
This recipe provided a quick overview on how to add the SeekBar widget to an Activity. It demonstrated how the Activity is notified of SeekBar events by using an event handler or by implementing SeekBar.IOnSeekBarChangeListener.