Button listener android kotlin

Android Button – setOnClickListener

Android Button setOnClickListener() function is used to execute code when user clicks or taps on the button.

Steps to call setOnClickListener() on Button

To execute a set of statements when user taps on Button widget, follow these steps.

  1. Get reference to the Button.
  2. Call setOnClickListener() on the Button reference. You can use lambda expression with setOnClickListener() function.
  3. Write the set of statements inside setOnClickListener() function block. This code block gets executed when a tap happens on the button.

The typical syntax to call setOnClickListener() on a Button is

val button = findViewById(R.id.button_id) button.setOnClickListener < //cdoe that executes when user taps on the button >

Example

Create an Android Application with Kotlin support and Empty Activity. Create a Button widget with id specified and text value taken from strings.xml.

 My App - kotlinandroid.org Submit 

activity_main.xml

In the kotlin file, we will set the Button’s setOnClickListener() function in MainActivity’s onCreate() function. We shall set the content view for the activity with the layout file, and then set the action listener for button.

When user clicks or taps on the button, we are just showing a Toast. You may replace this with your own code as required.

MainActivity.kt

package com.kotlinandroid.myapp import android.os.Bundle import android.widget.Button import android.widget.Toast import androidx.appcompat.app.AppCompatActivity class MainActivity : AppCompatActivity() < override fun onCreate(savedInstanceState: Bundle?) < super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) val button = findViewById(R.id.button_id) button.setOnClickListener < Toast.makeText(applicationContext,"You clicked Submit Button.",Toast.LENGTH_SHORT).show() >> >

Android Button - setOnClickListener

Click on the button. You will see a Toast made in the bottom area of the screen.

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Kotlin Android – Set OnClickListener for Button

Android Button widget is a UI element generally used to receive user actions as input. You can click on a Button, long press, etc.

In this tutorial, we shall learn to set OnClickListener for Button.

Code – Button.setOnClickListener()

Following code helps you to set on-click listener for Button.

// get reference to button val btn_click_me = findViewById(R.id.btn_click_me) as Button // set on-click listener btn_click_me.setOnClickListener

What we have done here is, we got the reference to the Button and then used setOnClickListener method to trigger an action when the button is clicked.

Example – Kotlin Androide Button.setOnClickListener()

Now we shall look into the layout xml file and Activity(Kotlin file) to set OnClickListener for a Button.

Create an Android Application with Kotlin Support and replace activity_main.xml and MainActivity.kt with the following content.

activity_main.xml

MainActivity.kt

package com.tutorialkart.myapplication import android.support.v7.app.AppCompatActivity import android.os.Bundle import android.widget.Button import android.widget.Toast class MainActivity : AppCompatActivity() < override fun onCreate(savedInstanceState: Bundle?) < super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) // get reference to button val btn_click_me = findViewById(R.id.btn_click_me) as Button // set on-click listener btn_click_me.setOnClickListener < // your code to perform when the user clicks on the button Toast.makeText(this@MainActivity, "You clicked me.", Toast.LENGTH_SHORT).show() >> >

Build and Run the Android Application. You would see the Android screen as shown in the following screenshot.

Set OnClickListener for Button in Kotlin Android - Kotlin Android Tutorial - www.tutorialkart.com

Action performed on clicking the button - Kotlin Android Tutorial - www.tutorialkart.com

Button.setOnClickListener() will be triggered and the code in this setOnClickListener<> block will run.

Conclusion

In this Android Tutorial – Kotlin Button OnclickListener, we have learnt to set OnClickListener for Button in Kotlin Android using Button. setOnClickListener() method.

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Android Button using Kotlin and XML

Android Button using Kotlin and XML

While we believe that this content benefits our community, we have not yet thoroughly reviewed it. If you have any suggestions for improvements, please let us know by clicking the “report an issue“ button at the bottom of the tutorial.

Android Button Overview

Android Button class extends TextView. Button is a UI widget that is used to get click interactions from the user to trigger an action in the application. A button can be created in the XML layout as well as the Kotlin Activity class in the Android Studio Project.

Creating a Button in XML Layout

  • android:id is used to set the unique identifier on the Button.
  • The android:text is used to set the text inside the button. By default text is displayed in capital letters.
  • android:onClick is used to define the Kotlin function to be invoked in the activity when the button is clicked. It is a click listener.
  • The android:background is used to set the background color/drawable on the Button.

Tip: To prevent displaying all letters in captial, use the attribute android:textAllCaps=»false»

For more details on how to customize your Buttons in XML Layout refer to the Android Buttons Tutorial.

Button Click Listeners

We can set button listeners programmatically too. Following are the two major listeners:

  1. setOnClickListener — triggers when a button is clicked.
  2. setOnLongClickListner — triggers when a button is pressed for a longer duration.

Following code snippets has the setOnClickListener set over a button.

button.setOnClickListener(object : View.OnClickListener < override fun onClick(v: View?) < //your implementation goes here >>) 

The above code can be converted in a lambda expression to make it short.

Similarly, a setOnLongClickListener can be defined in the following manner.

button.setOnLongClickListener < textView.text = "Androidly Button Long click" true >//or button.setOnLongClickListener

In the above code, the last statement in each of the expressions is the return statement.

  • If the setOnLongClickListener returns true, it means that the setOnClickListener won’t be triggered.
  • If the setOnLongClickListener returns false, it means that the setOnClickListener will be triggered.

This is known as consuming events. The first case consumes the event.

Android Button using Kotlin

We’ll be developing an application that increments the counter of the TextView on a Button click. We will use Kotlin to create the button. We’ll also learn about the different Button click handlers.

1. Project Structure

android button project structure

Create a new Android Studio Project. Ensure that in the initial setup, you enable Kotlin Support. Once you’re done, following is the Project Structure that you shall see.

2. Kotlin Button Code

The activity_main.layout file looks like the following code.

android button strings xml

We’ve used LinearLayout that holds the views linearly (horizontally or vertically). It’s recommended to set the strings in the strings.xml file instead of hardcoding them. To fetch a string resource we use @string/name_of_string . The function addOne(view: View) is defined in the MainActivity.kt Kotlin class. The code for the MainActivity.kt class is given below.

package net.androidly.androidlybuttons import android.support.v7.app.AppCompatActivity import android.os.Bundle import android.support.v4.content.ContextCompat import android.view.View import android.view.ViewGroup import android.widget.Button import android.widget.LinearLayout import kotlinx.android.synthetic.main.activity_main.* class MainActivity : AppCompatActivity(), View.OnClickListener < override fun onCreate(savedInstanceState: Bundle?) < super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) var androidlyButton = Button(this) androidlyButton.apply < layoutParams = LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT) text = "Double the value" setAllCaps(false) textSize = 20f >androidlyButton.setOnClickListener(this) linearLayout.addView(androidlyButton) androidlyButton = Button(this) androidlyButton.apply < layoutParams = LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT) text = "RESET" textSize = 20f setTextColor(ContextCompat.getColor(this@MainActivity, R.color.colorPrimaryDark)) setOnLongClickListener < txtCounter.text = 0.toString() true >> androidlyButton.setOnClickListener(this) linearLayout.addView(androidlyButton) > override fun onClick(v: View?) < when (v?.id) < R.id.btnDouble -> < txtCounter.text = (txtCounter.text.toString().toInt() * 2).toString() >R.id.btnReset -> < txtCounter.text = (-100).toString() >else -> < >> > fun addOne(view: View) < txtCounter.text = (txtCounter.text.toString().toInt() + 1).toString() >> 
  1. import kotlinx.android.synthetic.main.activity_main.* statement automatically gets the view IDs from the xml in our class. Hence saving us from using findViewById.
  2. The fun addOne(view: View) is triggered when the btnIncrementByOne is clicked. The (view: View) parameter must be defined in the function declaration.
  3. Create a Button programmatically and set it in the parent view(LinearLayout here) using the following code.

var androidlyButton = Button(this) linearLayout.addView(androidlyButton) 

android button ids

  • Instead of calling member functions on the Button class, we can use apply<> lambda expression.
  • The layoutParams is used to define the width and height of the button. The MATCH_PARENT sets the width/height equal to the linear layout. WRAP_CONTENT wraps the view to the size of the content.
  • We can set the id programmatically under res | values | ids.xml.
  • We’ve defined the View.OnClickListener interface in our MainActivity.kt class. Hence we need to override its onClick() function.
  • Inside the onClick function, we use the Kotlin when statement, which is equivalent to switch in other languages.
  • For the onClick function to be triggered, you must register the setOnClickListener over the button with the interface using the context( this ).
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