Kotlin Android Button

Android Button is a push button used to perform events on its click. It is a UI component comes under the android.widget.Button class. To learn more about Android Button refers to Android Button Example

Using Kotlin, we can perform events on Android Button though different ways, using:

1. Implement the setOnClickListener of Button

  button1.setOnClickListener(){              Toast.makeText(this,”button 1 clicked”, Toast.LENGTH_SHORT).show()          }  

2. Implement the View.OnClickListner and override its function

  button2.setOnClickListener(this)       . .      override fun onClick(view: View) {          //  TODO(“not implemented”) //To change body of created functions use File | Settings | File Templates.      }  

3. Adding the onClick attribute of Button in layout file and implement its function.

      <Button                  android:onClick=”clickButton”/>        fun clickButton(v: View){          val mToast = Toast.makeText(applicationContext,”button 3 clicked”, Toast.LENGTH_SHORT)          mToast.show()      }  

4. Create a Button programmatically and set it on the layout

  button4.setLayoutParams(ViewGroup.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT))          button4.setId(button4_Id)          button4.x = 250f          button4.y = 500f          button4.setOnClickListener(this)          constraintLayout.addView(button4)  

Kotlin Android Button Example

In this example, we will create the Button and performs event on them. Clicking on the Button, display a toast message.

activity_main.xml

Add the three Button from the Widgets palette in the activity_main.xml layout file. Its code is given below. The Button of id button3 added the onClick attribute and its function name is implemented in MainActivity class file.

  <?xml version=”1.0″ encoding=”utf-8″?>  <android.support.constraint.ConstraintLayout xmlns:android=”http://schemas.android.com/apk/res/android”      xmlns:app=”http://schemas.android.com/apk/res-auto”      xmlns:tools=”http://schemas.android.com/tools”      android:layout_width=”match_parent”      android:layout_height=”match_parent”      android:id=”@+id/constraintLayout”      tools:context=”example.tutoraspire.com.kotlinbutton.MainActivity”>      <TextView          android:layout_width=”wrap_content”          android:layout_height=”wrap_content”          android:text=”Button Action Example”          app:layout_constraintBottom_toBottomOf=”parent”          app:layout_constraintLeft_toLeftOf=”parent”          app:layout_constraintRight_toRightOf=”parent”          app:layout_constraintTop_toTopOf=”parent”          app:layout_constraintVertical_bias=”0.073″          android:textAppearance=”@style/Base.TextAppearance.AppCompat.Medium”/>        <Button          android:id=”@+id/button1″          android:layout_width=”95dp”          android:layout_height=”wrap_content”          android:layout_marginBottom=”8dp”          android:layout_marginEnd=”8dp”          android:layout_marginStart=”8dp”          android:layout_marginTop=”8dp”          android:text=”Button 1″          app:layout_constraintBottom_toBottomOf=”parent”          app:layout_constraintEnd_toEndOf=”parent”          app:layout_constraintHorizontal_bias=”0.501″          app:layout_constraintStart_toStartOf=”parent”          app:layout_constraintTop_toTopOf=”parent”          app:layout_constraintVertical_bias=”0.498″ />        <Button          android:id=”@+id/button2″          android:layout_width=”wrap_content”          android:layout_height=”wrap_content”          android:layout_marginBottom=”80dp”          android:layout_marginEnd=”8dp”          android:layout_marginStart=”8dp”          android:layout_marginTop=”8dp”          android:text=”Button 2″          app:layout_constraintBottom_toBottomOf=”parent”          app:layout_constraintEnd_toEndOf=”parent”          app:layout_constraintStart_toStartOf=”parent”          app:layout_constraintTop_toTopOf=”parent”          app:layout_constraintVertical_bias=”0.762″ />        <Button          android:id=”@+id/button3″          android:layout_width=”101dp”          android:layout_height=”48dp”          android:layout_marginBottom=”8dp”          android:layout_marginEnd=”8dp”          android:layout_marginStart=”8dp”          android:layout_marginTop=”8dp”          android:onClick=”clickButton”          android:text=”Button 3″          app:layout_constraintBottom_toBottomOf=”parent”          app:layout_constraintEnd_toEndOf=”parent”          app:layout_constraintHorizontal_bias=”0.502″          app:layout_constraintStart_toStartOf=”parent”          app:layout_constraintTop_toTopOf=”parent”          app:layout_constraintVertical_bias=”0.774″ />  </android.support.constraint.ConstraintLayout>  

MainActivity.kt

Add the following code in the MainActivity.kt class. In this class, we implement the setOnClickListener listener on the button, implements the OnClickListener of View class (View.OnClickListener) and override its function onClick. In this class, we also create a Button programmatically (button4), define its properties and set it on the layout.

  package example.tutoraspire.com.kotlinbutton    import android.support.v7.app.AppCompatActivity  import android.os.Bundle  import android.view.View  import android.view.ViewGroup  import android.widget.Button  import android.widget.Toast  import kotlinx.android.synthetic.main.activity_main.*    class MainActivity : AppCompatActivity() , View.OnClickListener {      val button4_Id: Int = 1111      override fun onCreate(savedInstanceState: Bundle?) {          super.onCreate(savedInstanceState)          setContentView(R.layout.activity_main)          button1.setOnClickListener(){              Toast.makeText(this,”button 1 clicked”, Toast.LENGTH_SHORT).show()          }          button2.setOnClickListener(this)          // add button dynamically          val button4 = Button(this)          button4.setText(“Button 4 added dynamically”)          button4.setLayoutParams(ViewGroup.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT))          button4.setId(button4_Id)          button4.x = 250f          button4.y = 500f          button4.setOnClickListener(this)          constraintLayout.addView(button4)      }      override fun onClick(view: View) {          //  TODO(“not implemented”) //To change body of created functions use File | Settings | File Templates.          when (view.id) {              R.id.button2 ->                  Toast.makeText(this,”button 2 clicked”, Toast.LENGTH_SHORT).show()//single line code              button4_Id->{//multiline code                  val myToast = Toast.makeText(this,”button 4 clicked”, Toast.LENGTH_SHORT)                  myToast.show()              }          }      }      fun clickButton(v: View){          val mToast = Toast.makeText(applicationContext,”button 3 clicked”, Toast.LENGTH_SHORT)          mToast.show()      }  }  

Output:

Kotlin Android Button

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Kotlin Android Button

Kotlin Android Button

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activity_main.xml

MainActivity.kt

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