Java android new button
Одним из часто используемых элементов являются кнопки, которые представлены классом android.widget.Button . Ключевой особенностью кнопок является возможность взаимодействия с пользователем через нажатия.
Некоторые ключевые атрибуты, которые можно задать у кнопок:
- text : задает текст на кнопке
- textColor : задает цвет текста на кнопке
- background : задает фоновый цвет кнопки
- textAllCaps : при значении true устанавливает текст в верхнем регистре. По умолчанию как раз и применяется значение true
- onClick : задает обработчик нажатия кнопки
Итак, изменим код в activity_main.xml следующим образом:
При помощью атрибута android:onClick можно задать метод в коде java, который будет обрабатывать нажатия кнопки. Так, в вышеприведенном примере это метод sendMessage . Теперь перейдем к коду MainActivity и пропишем в нем такой метод:
package com.example.viewapp; import androidx.appcompat.app.AppCompatActivity; import android.os.Bundle; import android.view.View; import android.widget.EditText; import android.widget.TextView; public class MainActivity extends AppCompatActivity < @Override protected void onCreate(Bundle savedInstanceState) < super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); >// Обработка нажатия кнопки public void sendMessage(View view) < TextView textView = findViewById(R.id.textView); EditText editText = findViewById(R.id.editText); textView.setText("Добро пожаловать, " + editText.getText()); >> При создании метода обработки нажатия следует учитывать следующие моменты:
- Метод должен объявляться с модификатором public
- Должен возвращать значение void
- В качестве параметра принимать объект View . Этот объект View и представляет собой нажатую кнопку
В данном случае после нажатия на кнопку в TextView выводится текст из EditText.
Аналогичный пример полностью в коде MainActivity:
package com.example.viewapp; import androidx.appcompat.app.AppCompatActivity; import androidx.constraintlayout.widget.ConstraintLayout; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.EditText; import android.widget.TextView; public class MainActivity extends AppCompatActivity < EditText editText; TextView textView; @Override protected void onCreate(Bundle savedInstanceState) < super.onCreate(savedInstanceState); //setContentView(R.layout.activity_main); ConstraintLayout constraintLayout = new ConstraintLayout(this); textView = new TextView(this); textView.setId(View.generateViewId()); ConstraintLayout.LayoutParams textViewLayout = new ConstraintLayout.LayoutParams( ConstraintLayout.LayoutParams.MATCH_CONSTRAINT, ConstraintLayout.LayoutParams.WRAP_CONTENT ); textViewLayout.topToTop = ConstraintLayout.LayoutParams.PARENT_ID; textViewLayout.leftToLeft = ConstraintLayout.LayoutParams.PARENT_ID; textViewLayout.rightToRight = ConstraintLayout.LayoutParams.PARENT_ID; textView.setLayoutParams(textViewLayout); constraintLayout.addView(textView); editText = new EditText(this); editText.setId(View.generateViewId()); editText.setHint("Введите имя"); ConstraintLayout.LayoutParams editTextLayout = new ConstraintLayout.LayoutParams( ConstraintLayout.LayoutParams.MATCH_CONSTRAINT, ConstraintLayout.LayoutParams.WRAP_CONTENT ); editTextLayout.topToBottom = textView.getId(); editTextLayout.leftToLeft = ConstraintLayout.LayoutParams.PARENT_ID; editTextLayout.rightToRight = ConstraintLayout.LayoutParams.PARENT_ID; editText.setLayoutParams(editTextLayout); constraintLayout.addView(editText); Button button = new Button(this); button.setText("Ввод"); ConstraintLayout.LayoutParams buttonLayout = new ConstraintLayout.LayoutParams( ConstraintLayout.LayoutParams.WRAP_CONTENT, ConstraintLayout.LayoutParams.WRAP_CONTENT ); buttonLayout.topToBottom = editText.getId(); buttonLayout.leftToLeft = ConstraintLayout.LayoutParams.PARENT_ID; button.setLayoutParams(buttonLayout); constraintLayout.addView(button); button.setOnClickListener(new View.OnClickListener() < public void onClick(View v) < // Обработка нажатия textView.setText("Добро пожаловать, " + editText.getText()); >>); setContentView(constraintLayout); > > При программном создании кнопки мы можем определить у нее слушатель нажатия View.OnClickListener и с помощью его метода onClick также обработать нажатие:
button.setOnClickListener(new View.OnClickListener() < public void onClick(View v) < // Обработка нажатия >>);
Android Button With Examples [Latest]
In this tutorial, we will look into Android Button. We will create android studio application and look into various things about button designing, styling, click events etc.
Android Button
Android Buttons are GUI components that the users can click upon to either goto the next screen, confirm an option/trigger any event created by you, the Android Developer.
The android.widget.Button is a subclass of Android TextView.
Buttons in Android can be of the following forms:
In the following sections, we’ll be discussing the default button class, creating it programmatically, styling it.
Creating Button in Layout
We can define the Button widget in our layout file in Android Studio in the following way.
In the above code, we’ve wrapped our Button widget inside a LinearLayout
The id represents the unique identifier.
The onClick attribute requires the method name as the value. This method name should be defined in the corresponding activity of the layout.
It’ll get triggered when the button is clicked.
Setting android:background as a color would remove the selection animation from the button.
We can set an image inside the button alongise the text by using the attribute android:drawableLeft to set the image to the left of the text.
Our MainActivity.java class looks like this:
Toast . makeText ( getApplicationContext ( ) , «Button is clicked» , Toast . LENGTH_LONG ) . show ( ) ;
On clicking the button a Toast notification would be displayed onto the screen.
Create Button Programmatically
Let’s set the attributes on the button programmatically and create one button programmatically.
We hook the xml button id to the corresponding instance in the class using the findViewById method.
setTextColor() is used to set the text color,
setClickable accepts a boolean value. Setting it to false would make the button not clickable and the clickMe method won’t be triggered.
Creating Button Programmatically
The following code creates a button programmatically and adds it to the root hierarchy.
Toast . makeText ( getApplicationContext ( ) , «Programmatic Button is clicked» , Toast . LENGTH_LONG ) . show ( ) ;
We can set an ID programmatically using setId. We can create ids in the folder res | values | ids.xml as shown below:
setOnClickListener has an interface callback that listens for the click and triggers the onClick method whenever the button is clicked.
Now let’s add another buttons in our layout programmatically in our MainActivity.java class.
Toast . makeText ( getApplicationContext ( ) , «Programmatic Button is clicked» , Toast . LENGTH_LONG ) . show ( ) ;
programmaticButton . setBackgroundColor ( ContextCompat . getColor ( this , R . color . colorAccent ) ) ;
Toast . makeText ( getApplicationContext ( ) , «Another Programmatic Button is clicked» , Toast . LENGTH_LONG ) . show ( ) ;
setBackgroundColor() method is to set a color on the button programmatically.
Ideally, we should use string resources to set text on the button instead of hardcoding them in the java class itself.
In the above code, we’ve created two buttons and each of them has a separate interface callback for the listener. This means we’ll have a different object created in the memory for each of the buttons. This would add up in the heap memory and eventually the application would use more memory than required from the device. We can fix this performance issue by making the class implement the View.OnClickListener itself.
Instead of using separate setOnClickListener callbacks for every Button, implement the interface on the class itself.
So with the View.OnClickListener implemented in the class itself, our MainActivity.java class would look like this:
Java android new button
In Android, Button represents a push button. A Push buttons can be clicked, or pressed by the user to perform an action. There are different types of buttons used in android such as CompoundButton, ToggleButton, RadioButton.
Button is a subclass of TextView class and compound button is the subclass of Button class. On a button we can perform different actions or events like click event, pressed event, touch event etc.
Android buttons are GUI components which are sensible to taps (clicks) by the user. When the user taps/clicks on button in an Android app, the app can respond to the click/tap. These buttons can be divided into two categories: the first is Buttons with text on, and second is buttons with an image on. A button with images on can contain both an image and a text. Android buttons with images on are also called ImageButton.
Button code in XML:
The below code will create Button and write “Abhi Android” text on it.
Attributes of Button in Android:
Now let’s we discuss some important attributes that helps us to configure a Button in your xml file (layout).
1. id: id is an attribute used to uniquely identify a text Button. Below is the example code in which we set the id of a Button.
2. gravity: The gravity attribute is an optional attribute which is used to control the alignment of the text like left, right, center, top, bottom, center_vertical, center_horizontal etc.
Below is the example code with explanation included in which we set the right and center vertical gravity for text of a Button.
3. text: text attribute is used to set the text in a Button. We can set the text in xml as well as in the java class.
Below is the example code with explanation included in which we set the text “Learning Android @ AbhiAndroid” in a Button.
Setting Text Using Java class:
Below is the example code in which we set the text on Button programmatically means in java class. The output will be same as the above.
Button button = (Button) findViewById(R.id.simpleButton); button.setText("Learn Android @ AbhiAndroid");//set the text on button 4.textColor: textColor attribute is used to set the text color of a Button. Color value is in the form of “#argb”, “#rgb”, “#rrggbb”, or “#aarrggbb”.
Below is the example code with explanation included in which we set the red color for the displayed text of a Button.
Setting Text Color On Button Inside Java class:
Below is the example code in which we set the text color of a Button programmatically means in java class.
Button simpleButton=(Button) findViewById(R.id.simpleButton); simpleButton.setTextColor(Color.RED);//set the red color for the text
5. textSize: textSize attribute is used to set the size of the text on Button. We can set the text size in sp(scale independent pixel) or dp(density pixel).
Below is the example code in which we set the 25sp size for the text of a Button.
Setting textSize In Java class:
Below is the example code in which we set the text size of a Button programmatically means in java class.
Button simpleButton=(Button)findViewById(R.id.simpleButton); simpleButton.setTextSize(25);//set the text size of button
6. textStyle: textStyle attribute is used to set the text style of a Button. The possible text styles are bold, italic and normal. If we need to use two or more styles for a Button then “|” operator is used for that.
Below is the example code with explanation included, in which we set the bold and italic text styles for text of a button.
7. background: background attribute is used to set the background of a Button. We can set a color or a drawable in the background of a Button.
Below is the example code in which we set the gren color for the background, Black color for the displayed text and set 15dp padding from all the side’s for Button.
Setting background in Button In Java class:
Below is the example code in which we set the background color of a Button programmatically means in java class.
Button simpleButton=(Button)findViewById(R.id.simpleButton); simpleButton.setBackgroundColor(Color.BLACK);//set the black color of button background
8. padding: padding attribute is used to set the padding from left, right, top or bottom. In above example code of background we also set the 10dp padding from all the side’s of button.
9. drawableBottom: drawableBottom is the drawable to be drawn to the below of the text.
Below is the example code in which we set the icon to the below of the text.
Make sure you have image saved in your drawable folder name ic_launcher.
10. drawableTop, drawableRight And drawableLeft: Just like the above attribute we can draw drawable to the left, right or top of text.
In the Below example we set the icon to the right of the text. In the same way you can do for other two attribute by your own:
Button Example In Android Studio:
Below is the example of button in which we display two buttons with different background and whenever a user click on the button the text of the button will be displayed in a toast.
Step 1: Create a new project in Android Studio and name it ButtonExample.
Select File -> New -> New Project and Fill the forms and click "Finish" button.
Step 2: Now open res -> layout -> xml (or) activity_main.xml and add following code. Here we are designing the UI of two button in Relative Layout.
Step 3: Now Open app -> package -> MainActivity.java and the following code. Here using setOnClickListener() method on button and using Toast we will display which button is clicked by user.
package example.abhiandriod.buttonexample; import android.support.v7.app.AppCompatActivity; import android.os.Bundle; import android.view.Menu; import android.view.MenuItem; import android.view.View; import android.widget.Button; import android.widget.Toast; public class MainActivity extends AppCompatActivity < Button simpleButton1, simpleButton2; @Override protected void onCreate(Bundle savedInstanceState) < super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); simpleButton1 = (Button) findViewById(R.id.simpleButton1);//get id of button 1 simpleButton2 = (Button) findViewById(R.id.simpleButton2);//get id of button 2 simpleButton1.setOnClickListener(new View.OnClickListener() < @Override public void onClick(View view) < Toast.makeText(getApplicationContext(), "Simple Button 1", Toast.LENGTH_LONG).show();//display the text of button1 >>); simpleButton2.setOnClickListener(new View.OnClickListener() < @Override public void onClick(View view) < Toast.makeText(getApplicationContext(), "Simple Button 2", Toast.LENGTH_LONG).show();//display the text of button2 >>); > >
Now start the AVD in Emulator and run the App. You will see two button. Click on any button and you will see the message on screen which button is clicked.