Button onclick android kotlin

Setup Android Button programmatically in Kotlin

In this article, we will explore how to set up buttons programmatically in an Android application. We will cover various aspects such as finding buttons by their IDs, setting click listeners, adding or removing buttons dynamically, enabling or disabling buttons, and showing or hiding buttons programmatically. Additionally, we will delve into customizing the background color, borders, and text attributes of buttons using code. By the end of this article, you’ll have a comprehensive understanding of how to manipulate buttons programmatically in your Android projects. Let’s dive in!

Setup Programmatically

Get Button with FindViewById

All views defined in XML layout can be accessed programmatically by calling the findViewById method. You must however give your view, in this case, your button, an identifier, which can later be accessed with the resource bundle R.id . The following code illustrates how a button can be found with the findViewById method.

val button: Button = findViewById(R.id.buttonId) val button = findViewById(R.id.buttonId)

Kotlin also provides additional functionality to access views that are defined in XML without calling the findViewById method.

import kotlinx.android.synthetic.main.YOUR_LAYOUT_NAME. override fun onCreate(savedInstanceState: Bundle?)

Set OnClickListener

In this section, you will also learn how to react to click events on your button. You will see how to handle these events and will give examples of how to make your button clickable or not clickable, or in other words, enabled and disabled. Android buttons provide an observer object to which you can register OnClickListener or call-back functions. These functions will be executed every time somebody clicks on this widget. If you want to know how the Listener Pattern works, we suggest having look at our detailed tutorial about this design pattern: Observer Pattern. You can find several examples of how to register and set a listener in our examples below. All you need to make sure of is to have a valid reference to your view.

Add / remove button programmatically

As with any widget, buttons can be added or removed programmatically in Kotlin. All you need is a valid layout, in which the button will be added / removed. In our example below we have defined 2 buttons and one vertical layout in XML. We get the references to these objects via the findViewById method. The click event handler of the addBtn will declare a new button and insert it at the end of the layout. The removeBtn will get the index of the last button in the layout and (if possible) remove it. Note that we could derive custom classes from the button base class and completely configure our buttons programmatically.

class MainActivity : AppCompatActivity() < var addBtn: Button? = null var removeBtn: Button? = null var listView: LinearLayout? = null override fun onCreate(savedInstanceState: Bundle?) < super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) addBtn = findViewById(R.id.addBtn) removeBtn = findViewById(R.id.removeBtn) listView = findViewById(R.id.listView) addBtn. setOnClickListener < addButton() >removeBtn. setOnClickListener < removeButton() >> private fun addButton() < val newButton = Button(this); newButton.text = "New Button: " + listView. childCount listView. addView(newButton) >private fun removeButton() < val lastIndex = listView. childCount - 1; if(lastIndex < 0) return listView. removeViewAt(lastIndex) >>

Enable / disable button programmatically

Buttons can be enabled or disabled. Enabled widgets will no longer react to click events, while enable widgets will handle such events. In our example, we have declared 2 buttons in the XML layout. We are getting their references with the findViewById function. On the click event listener of, in the enableBtn we are setting the isClickable property of our target button to true . In the disbledBtn we are setting it to false . The extra text view provides information if the button was clicked.

class MainActivity : AppCompatActivity() < var enableBtn: Button? = null var disableBtn: Button? = null var targetBtn: Button? = null var infoText: TextView? = null var clickCount = 0 override fun onCreate(savedInstanceState: Bundle?) < super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) enableBtn = findViewById(R.id.enableBtn) disableBtn = findViewById(R.id.disableBtn) targetBtn = findViewById(R.id.target) infoText = findViewById(R.id.infoText) enableBtn. setOnClickListener < targetBtn. isClickable = true >disableBtn. setOnClickListener < targetBtn. isClickable = false >targetBtn. setOnClickListener < infoText. text = "Click count: " + ++clickCount>> >

Show / hide button programmatically

Views in Android can be hidden or shown. Their appearance can be controlled with the visibility property. This property needs an interger which defines their state. The integer value can be accessed via static fields in the View class. The table below shows the current integer representation. In our example, we have created 3 buttons in XML Layout. We get the references as usual with the findViewById function. The showBtn will set the visibility flag of the targetBtn to View.VISIBLE and the hideBtn to View.INVISIBLE , respectively.

Static Field	Const int Value
View.VISIBLE	0
View.INVISIBLE	4

class MainActivity : AppCompatActivity() < var showBtn: Button? = null var hideBtn: Button? = null var targetBtn: Button? = null override fun onCreate(savedInstanceState: Bundle?) < super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) showBtn = findViewById(R.id.showBtn) hideBtn = findViewById(R.id.hideBtn) targetBtn = findViewById(R.id.target) showBtn. setOnClickListener < targetBtn. visibility = View.VISIBLE >hideBtn. setOnClickListener < targetBtn. visibility = View.INVISIBLE >> >

Background

Android provides functionality to define your background of your button either in XML or programmatically in code.

Background Color

One common use case is to change the default color of an Android button. You can do this either in XML by setting the desired property. The alternative is to get a reference of your button programatically and then set the background color with the setBackgroundColor function of the object. You can get a reference of this object if it is created in XML by using the findViewById method. Android offers several ways to create colors. We will show you with examples how to create a color from different color codes.

RGB color codes are the most common representations of colors. Android offers 2 overload functions of Color.rgb() . The first accepts integer values with a range from 0 to 255. The other accepts floating point values in a range from 0 to 1.0. In our example we adapt the red channel of the background color.

private fun createButton(red: Int) : Button

RGBA or in Android ARGB is just like RGB color codes but with an additional channel for transparency. If you don’t need transparency we recommend using RGB values directly, as RGBA uses more memory. However, you can use this option to create a fully transparent button as shown below.

private fun createButton(red: Int) : Button

An alternative to RGB values is to use directly the HEX color code. You can parse the color object with the function Color.parseColor(string) which accepts the hex color code as shown below.

 private fun createButton(hex: String = "#646400") : Button

Transparent Background Color

The easiest way to set programmatically a transparent background color is to use an RGBA color, where the alpha channel is 0. This will create a completely transparent color. In the example below you will see the effect of different alpha channels.

private fun createButton(alpha: Int) : Button

Another option is to adapt the alpha channel directly on the Background drawable. The drawable object provides a property alpha which can be set to 0 for full transparency. The result is the same as using RGBA values. This method is the preferred way if you don’t want to create new extra colors.

private fun createButton(alpha: Int) : Button

Border

Defining the border of a button in Android can be quite a challenge. Especially if you want or need to do it programmatically. To setup correctly your border, you first need to have a reference to your button. You can either find an existing button, which is defined in XML Layout with the findViewById function or you can create a new one directly in your Kotlin code.

Afterward you need to define manually the background. The background property accepts a Drawable object. You can create a new one or use existing ones from the Android ecosystem.

Set Border Width programmatically

As an example how to set the border width programmatically in code, you can use a ShapeDrawable . In our example, we use such a drawable with an actual rectangle shape. The drawable exposes a paint instance that finally exposes properties to change border width. The property to set the border width programmatically is the strokeWidth property on the paint instance.

In the code example below we have created a linear layout in XML. In Kotlin code we reference (by findViewById ) and it in a for-loop 5 buttons. Each button has a different border width. The result can be seen in the next image.

class MainActivity : AppCompatActivity() < var listView: LinearLayout? = null override fun onCreate(savedInstanceState: Bundle?) < super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) listView = findViewById(R.id.layout) for (strokeWidth in 1..5) < listView. addView(createButton(strokeWidth * 10)) >> private fun createButton(borderWidth: Int) : Button < var button = Button(this); button.layoutParams = createParams() button.background = createBorderBackground(borderWidth) button.text = "BorderWidth: $borderWidth" return button >private fun createParams() : ViewGroup.LayoutParams < var left = 100 var right = 100 var top = 20 var bottom = 20 val params = ConstraintLayout.LayoutParams( ConstraintLayout.LayoutParams.MATCH_PARENT, ConstraintLayout.LayoutParams.WRAP_CONTENT ) params.setMargins(left, top, right, bottom) return params >private fun createBorderBackground(borderWidth: Int) : Drawable < val shapeDrawable = ShapeDrawable() shapeDrawable.shape = RectShape() shapeDrawable.paint.color = Color.BLACK shapeDrawable.paint.style = Paint.Style.STROKE shapeDrawable.paint.strokeWidth = borderWidth.toFloat(); return shapeDrawable >>

Set Border Radius / Corner Radius programmatically

Similar to the border width, the border-radius can be programmatically defined. This is the use case to create round corners. First, you need as well access to the correct drawable, which will be the background of our button. In this case, we are using a GradientDrawable , as it exposes the property cornerRadius property. Similar to the previous code we are creating several views and modifying the border-radius programmatically. The result can be seen in the next image.

class MainActivity : AppCompatActivity() < var listView: LinearLayout? = null override fun onCreate(savedInstanceState: Bundle?) < super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) listView = findViewById(R.id.layout) for (borderRadius in 1..5) < listView. addView(createButton(borderRadius * 10)) >> private fun createButton(borderRadius: Int) : Button < var button = Button(this); button.layoutParams = createParams() button.background = createBorderBackground(borderRadius) button.text = "BorderRadius: $borderRadius" return button >private fun createParams() : ViewGroup.LayoutParams < var left = 100 var right = 100 var top = 20 var bottom = 20 val params = ConstraintLayout.LayoutParams( ConstraintLayout.LayoutParams.MATCH_PARENT, ConstraintLayout.LayoutParams.WRAP_CONTENT ) params.setMargins(left, top, right, bottom) return params >private fun createBorderBackground(borderRadius: Int) : Drawable < var gradientDrawable = GradientDrawable() gradientDrawable.cornerRadius = borderRadius.toFloat() gradientDrawable.setColor(Color.LTGRAY) return gradientDrawable >>

Источник

Kotlin Android Button: работа с кнопками на примерах

Kotlin Android Button — это кнопка, используемая для выполнения событий и обработки при ее нажатии. Это компонент пользовательского интерфейса, относящийся к классу android.widget.Button. Чтобы узнать больше о кнопке Android, обратитесь к примеру кнопки Android.

Используя Котлин, мы можем выполнять события на кнопке Android разными способами:

1. Реализация setOnClickListener кнопки

button1.setOnClickListener()

2. Реализация View.OnClickListner и переопределение его функции.

button2.setOnClickListener(this) . . override fun onClick(view: View) < // TODO("not implemented") //To change body of created functions use File | Settings | File Templates. >

3. Добавление атрибута onClick кнопки в файл макета и реализация его функции.

4. Программное создание кнопки и установка ее на макете.

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)

Пример Kotlin Android Button

В этом примере мы создадим кнопку и выполним для нее событие. Нажав на кнопку, отобразится всплывающее сообщение.

Activity_main.xml

Добавьте три кнопки из палитры виджетов в файл макета activity_main.xml. Его код приведен ниже. Кнопка с идентификатором button3 добавила атрибут onClick, а имя ее функции реализовано в файле класса MainActivity.

MainActivity.kt

Добавьте следующий код в класс MainActivity.kt. В этом классе мы реализуем прослушиватель setOnClickListener для кнопки, реализуем OnClickListener класса View(View.OnClickListener) и переопределяем его функцию onClick. В этом классе мы также программно создаем кнопку(button4), определяем ее свойства и устанавливаем на макете.

package example.javatpoint.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-> > > fun clickButton(v: View) < val mToast = Toast.makeText(applicationContext,"button 3 clicked", Toast.LENGTH_SHORT) mToast.show() >>

Источник