Android press back button programmatically

How to Listen for Volume Button and Back Key Events Programmatically in Android?

By production, Android devices are provided with specific physical keys, such as Volume keys, Power key, Back key, Home key, and Activities key. These keys respond to a press. The same keys have particular functionality on the nature of the press. The volume key on a Single press increases or decreases the volume by some amount. Similarly, the Power key on a Single press locks the device, but on a Long press, Switches on or off the device. This article will create an application that responds to key press and generates a message confirming the same. This idea can further be implemented for creating useful applications:

1. Gaming Applications: Physical keys could be used for desired actions in Games.
2. Ambiance: Volume keys could be used to increase or decrease the screen’s brightness rather than doing it the traditional way.
3. Shortcuts to other Applications: Google Assistant pops up when the home key is pressed for long, similar shortcuts can be made.

This article aims to breach through the codes of this process and use the same keys for creating any desired applications or features. The codes’ scope explained in the latter section of the article is limited to the application that we will create. The created feature or functionality will work only inside the application. A sample GIF is given below to get an idea about what we are going to do in this article . Note that we are going to implement this project using the Kotlin language.

Steps to Listen for Volume Button and Back Key Events Programmatically

Step 1: Create a New Project

To create a new project in Android Studio please refer to How to Create/Start a New Project in Android Studio. Note that select Kotlin as the programming language.

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Buttons

A button consists of text or an icon (or both text and an icon) that communicates what action occurs when the user touches it.

Depending on whether you want a button with text, an icon, or both, you can create the button in your layout in three ways:

• With text, using the Button class:
• With an icon, using the ImageButton class:
• With text and an icon, using the Button class with the android:drawableLeft attribute:

Key classes are the following:

Responding to Click Events

When the user clicks a button, the Button object receives an on-click event.

To define the click event handler for a button, add the android:onClick attribute to the element in your XML layout. The value for this attribute must be the name of the method you want to call in response to a click event. The Activity hosting the layout must then implement the corresponding method.

For example, here’s a layout with a button using android:onClick :

Within the Activity that hosts this layout, the following method handles the click event:

Kotlin

The method you declare in the android:onClick attribute must have a signature exactly as shown above. Specifically, the method must:

• Be public
• Return void
• Define a View as its only parameter (this will be the View that was clicked)

Using an OnClickListener

You can also declare the click event handler programmatically rather than in an XML layout. This might be necessary if you instantiate the Button at runtime or you need to declare the click behavior in a Fragment subclass.

To declare the event handler programmatically, create an View.OnClickListener object and assign it to the button by calling setOnClickListener(View.OnClickListener) . For example:

Kotlin

Styling Your Button

The appearance of your button (background image and font) may vary from one device to another, because devices by different manufacturers often have different default styles for input controls.

You can control exactly how your controls are styled using a theme that you apply to your entire application. For instance, to ensure that all devices running Android 4.0 and higher use the Holo theme in your app, declare android:theme=»@android:style/Theme.Holo» in your manifest’s element. Also read the blog post, Holo Everywhere for information about using the Holo theme while supporting older devices.

To customize individual buttons with a different background, specify the android:background attribute with a drawable or color resource. Alternatively, you can apply a style for the button, which works in a manner similar to HTML styles to define multiple style properties such as the background, font, size, and others. For more information about applying styles, see Styles and Themes.

Borderless button

One design that can be useful is a «borderless» button. Borderless buttons resemble basic buttons except that they have no borders or background but still change appearance during different states, such as when clicked.

To create a borderless button, apply the borderlessButtonStyle style to the button. For example:

Custom background

If you want to truly redefine the appearance of your button, you can specify a custom background. Instead of supplying a simple bitmap or color, however, your background should be a state list resource that changes appearance depending on the button’s current state.

You can define the state list in an XML file that defines three different images or colors to use for the different button states.

To create a state list drawable for your button background:

Create three bitmaps for the button background that represent the default, pressed, and focused button states.

To ensure that your images fit buttons of various sizes, create the bitmaps as Nine-patch bitmaps.

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Buttons

A button consists of text or an icon (or both text and an icon) that communicates what action occurs when the user touches it.

Depending on whether you want a button with text, an icon, or both, you can create the button in your layout in three ways:

• With text, using the Button class:
• With an icon, using the ImageButton class:
• With text and an icon, using the Button class with the android:drawableLeft attribute:

Key classes are the following:

Responding to Click Events

When the user clicks a button, the Button object receives an on-click event.

To define the click event handler for a button, add the android:onClick attribute to the element in your XML layout. The value for this attribute must be the name of the method you want to call in response to a click event. The Activity hosting the layout must then implement the corresponding method.

For example, here’s a layout with a button using android:onClick :

Within the Activity that hosts this layout, the following method handles the click event:

Kotlin

The method you declare in the android:onClick attribute must have a signature exactly as shown above. Specifically, the method must:

• Be public
• Return void
• Define a View as its only parameter (this will be the View that was clicked)

Using an OnClickListener

You can also declare the click event handler programmatically rather than in an XML layout. This might be necessary if you instantiate the Button at runtime or you need to declare the click behavior in a Fragment subclass.

To declare the event handler programmatically, create an View.OnClickListener object and assign it to the button by calling setOnClickListener(View.OnClickListener) . For example:

Kotlin

Styling Your Button

The appearance of your button (background image and font) may vary from one device to another, because devices by different manufacturers often have different default styles for input controls.

You can control exactly how your controls are styled using a theme that you apply to your entire application. For instance, to ensure that all devices running Android 4.0 and higher use the Holo theme in your app, declare android:theme=»@android:style/Theme.Holo» in your manifest’s element. Also read the blog post, Holo Everywhere for information about using the Holo theme while supporting older devices.

To customize individual buttons with a different background, specify the android:background attribute with a drawable or color resource. Alternatively, you can apply a style for the button, which works in a manner similar to HTML styles to define multiple style properties such as the background, font, size, and others. For more information about applying styles, see Styles and Themes.

Borderless button

One design that can be useful is a «borderless» button. Borderless buttons resemble basic buttons except that they have no borders or background but still change appearance during different states, such as when clicked.

To create a borderless button, apply the borderlessButtonStyle style to the button. For example:

Custom background

If you want to truly redefine the appearance of your button, you can specify a custom background. Instead of supplying a simple bitmap or color, however, your background should be a state list resource that changes appearance depending on the button’s current state.

You can define the state list in an XML file that defines three different images or colors to use for the different button states.

To create a state list drawable for your button background:

Create three bitmaps for the button background that represent the default, pressed, and focused button states.

To ensure that your images fit buttons of various sizes, create the bitmaps as Nine-patch bitmaps.

Источник