What is SeekBar in android?

ByJael Lawler

What is a SeekBar in Android?

A SeekBar is a user interface element in Android that allows users to select from a range of values by sliding a “thumb” indicator left or right. SeekBars are useful when you want the user to be able to smoothly select a value within a range, like volume control or screen brightness.

The SeekBar is a subclass of ProgressBar, but functions differently in that it allows touch interaction to set the value. Internally, a SeekBar maintains a progress level from 0 to max and a thumb indicator the user can slide. As the user drags the thumb, the SeekBar will continuously receive touch events and update the progress level.

Some key features of SeekBar in Android:

  • Allows selecting a value in a range by sliding the thumb
  • Values can be integers or floating point numbers
  • Continuously updated as user slides thumb
  • Customizable thumb image and color

So in summary, a SeekBar in Android allows for smoothly selecting a value within a range through direct touch interaction. It’s perfect for use cases like media playback, volume control, and settings where you want the user to seamlessly set a value.

Creating a Simple SeekBar

A SeekBar can be added to a layout file or created programmatically. To initialize a basic SeekBar, first declare it in your layout XML file with the SeekBar tag. Set attributes like the max value, initial progress, thumb drawable, etc. For example:

<SeekBar 
    android:id="@+id/seekBar"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" 
    android:max="100"
    android:progress="25"
    android:thumb="@drawable/thumb_image"/>

This creates a SeekBar with id seekBar, width set to match parent, height wrapped to content, max value 100, initial progress 25, and a custom thumb image. You can also set these attributes in code after getting a reference to the SeekBar object.

To get the SeekBar instance in your activity, do:

SeekBar seekBar = findViewById(R.id.seekBar);

Then call methods like setMax(), setProgress(), setThumb() to customize the SeekBar. This covers the basics of initializing a SeekBar and setting common attributes.

Responding to SeekBar Changes

To get notified of changes and updates to the SeekBar, you need to attach an OnSeekBarChangeListener. This listener provides callbacks when the progress level changes, so you can perform actions based on the new value.

First, implement OnSeekBarChangeListener in your Activity or Fragment class. Then set the listener on the SeekBar using setOnSeekBarChangeListener(). For example:


seekBar.setOnSeekBarChangeListener(this);

There are 3 callback methods you need to implement:

  • onProgressChanged() – Called when the progress level changes. Use this to update other UI elements.
  • onStartTrackingTouch() – Called when the user first starts dragging the seekbar.
  • onStopTrackingTouch() – Called when the user stops dragging the seekbar.

To get the current progress value, use getProgress() on the SeekBar. For example:


int progress = seekBar.getProgress();

By implementing these callback methods, you can seamlessly update other UI elements, like a TextView, to display the seekbar’s progress.

Source: Handling SeekBar Changes in Android

Customizing the SeekBar

There are several ways to customize the appearance of a SeekBar in Android to match the look and feel of your app. Some common customizations include changing the colors, thumb drawable, background, and padding.

To change the color of the progress bar, you can use the android:progressTint and android:progressBackgroundTint attributes in XML. For example:


<SeekBar 
    android:progressTint="@color/pink"
    android:progressBackgroundTint="@color/gray" />

This will set the progress color to pink and the background color to gray [1].

You can also customize the thumb drawable which is the handle that users drag along the bar. This is done with android:thumb attribute:


<SeekBar
    android:thumb="@drawable/custom_thumb" />

Where custom_thumb is a drawable resource in your project [1].

To change the background, use the android:background attribute. And for padding, use android:padding or android:paddingLeft etc.

Additionally, you can make the SeekBar vertical by setting android:rotation to “270” degrees [2].

Using SeekBar for Media Playback

The SeekBar is commonly used to control media playback in Android apps. It allows users to scrub through audio or video content and jump to any part of the media file.

To implement SeekBar media playback control, you need to link the SeekBar to a MediaPlayer instance. The MediaPlayer handles loading and playing the media file. The SeekBar is updated periodically to reflect the current playback position. You can also call MediaPlayer methods like pause(), start(), seekTo() when the user drags the SeekBar thumb.

Some key steps for implementing SeekBar media playback:

  1. Get the media file duration and set it as the SeekBar max.
  2. Create a Runnable to update the SeekBar progress periodically.
  3. Attach an OnSeekBarChangeListener to handle drag events.
  4. In the listener, call MediaPlayer.seekTo() when the progress changes.
  5. Update the SeekBar max, progress, and buffer visually.

With this implementation, you can deliver precise scrubbing and an accurate portrayal of media playback progress to users.

SeekBar in Dialogs

Adding a SeekBar to an AlertDialog or DialogFragment is a common use case for SeekBars in Android. This allows you to collect continuous user input through the dialog. For example, you may want the user to select a volume level or brightness setting through a dialog SeekBar. Here are the steps to add a SeekBar to a dialog:

1. Create an AlertDialog or DialogFragment as usual. In the content View or layout for the dialog, include a SeekBar. Make sure to give it an id like @+id/dialog_seekbar.

2. In the Activity or Fragment code, retrieve the SeekBar from the dialog’s inflated View. For example:

SeekBar seekBar = dialog.findViewById(R.id.dialog_seekbar);

3. Set a ChangeListener on the SeekBar to respond when the user drags the thumb:

seekBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {

@Override

public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {

// Update UI based on progress

}

// …other interface methods

});

4. Update the UI or take other actions within onProgressChanged() when the SeekBar value changes. For example, you may update a text view to display the current value.

5. Call show() on the AlertDialog or DialogFragment to display it along with the SeekBar.

This allows you to conveniently add a SeekBar for continuous input in a dialog without needing a full Activity or custom view. Just be sure to retrieve the SeekBar from the dialog’s layout and set a listener to handle changes.

Sources:

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Vertical SeekBar

By default, the SeekBar in Android is horizontally oriented. However, it is possible to create a vertical SeekBar by setting the android:rotation property to “-90” (or “90” for right-to-left languages).

For example:

This rotates the SeekBar 90 degrees counterclockwise to make it vertical. All other properties like android:max, android:progress, etc. can be used as normal.

There are some open source implementations for vertical SeekBars like Vertical SeekBar that handle custom drawables and thumb positioning.

Overall, the vertical SeekBar follows the same principles and coding patterns as the default horizontal version. Just set android:rotation and adjust layout parameters as needed.

Common Issues

SeekBars can present some usability and accessibility challenges if not implemented carefully. Here are some common issues and how to troubleshoot them:

Touch Target Size

The touch target size of the SeekBar thumb can sometimes be too small, making it difficult to grab and drag on smaller screens. To fix this, increase the android:thumb offset and height to provide a larger touch area.

Focus

By default, SeekBars are not focusable via touch or navigation. To make them accessible, set android:focusable=”true” and android:focusableInTouchMode=”true” on the SeekBar view. Be sure to also provide Focus Handlers via the android:nextFocus… attributes.

Jumping Values

Sometimes the SeekBar value can jump unexpectedly when dragged. This is often due to discrete increments being used without proper smoothing. Try using smaller increments or enabling setSmoothScrollingEnabled(true) to fix.

Not Updating

If the SeekBar is not updating to reflect changes in the media playback position, make sure to continuously call setProgress() to update it. Also check that the proper max value and increments are set.

With some tweaking and testing on different devices, most SeekBar usability issues can be resolved. Pay special attention to sizing, increments, and focus/touch handling for full accessibility.

Accessibility Considerations

When using a SeekBar in an Android app, it is important to ensure it is accessible to users with disabilities, especially those who are blind or have low vision. The main accessibility considerations for SeekBar are:

1. Add a content description to describe what the SeekBar is for. This allows screen readers to announce the purpose of the SeekBar to blind users.

For example:
android:contentDescription="@string/volume_control"

2. Make sure the SeekBar can receive keyboard focus and be controlled with a D-pad or trackball for users who cannot use touch gestures. The default SeekBar implementation supports this.

3. Increase the touch target size of the SeekBar thumb for users with motor impairments. This makes it easier to grab the thumb control.

4. Announce changes to the SeekBars value via text-to-speech or other feedback for blind users. For example, you could announce the volume level or media playback position when it changes.

5. Allow sufficient time for users to seek to a new position before performing associated actions. For example, don’t start media playback as soon as the user stops touching the SeekBar thumb.

With some thoughtful design, SeekBars can be made easy to use for all users. Testing with screen readers and following Android accessibility guidelines helps ensure your SeekBar implementation is inclusive.

Summary

SeekBar in Android allows users to select a value from a range by dragging a slider thumb. Key points include:

  • SeekBar is implemented with the SeekBar class in Android.
  • To respond to SeekBar changes, implement an OnSeekBarChangeListener.
  • Customizations like color, thumb drawable, tick marks etc. can be done via XML attributes.
  • For media playback, SeekBar is commonly used to allow seeking to different positions in the media.
  • Vertical SeekBars can be created by setting the android:rotation attribute.
  • Accessibility should be considered by announcing value changes for screen readers.

Overall, SeekBar provides a convenient way for users to select values in a range and is highly customizable to fit many use cases in Android apps.

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