Android Button Tutorial
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In Android, Button is a "user interface control" which is used to perform an action when the user clicks on it.
In the class hierarchy, Button is a subclass of TextView, so it inherits all the features of a TextView.
android:textAllCaps
By default, when displaying content, the text of Button will be turned into uppercase; therefore, you should set android:textAllCaps="false" to ensure that the text content will be correctly displayed as the original.
<Button
android:id="@+id/button3"
android:text="Alarm"
android:drawableLeft="@drawable/icon_alarm"
android:textAllCaps="false"
... />
android:gravity
The android:gravity attribute is used to set the text display position of a Button. Its value is a combination of the following values:
| Constant in Java | Value | Description |
| Gravity.LEFT | left | |
| Gravity.CENTER_HORIZONTAL | center_horizontal | |
| Gravity.RIGHT | right | |
| Gravity.TOP | top | |
| Gravity.CENTER_VERTICAL | center_vertical | |
| Gravity.BOTTOM | bottom | |
| Gravity.START | start | |
| Gravity.END | end | |
| Gravity.CENTER | center | |
<Button
android:id="@+id/button"
android:gravity="center_horizontal|top"
android:text="Text"
... />
Icon - android:drawableLef, android:drawableTop,..
Android allows you to add four icons into a Button through the attributes of android:drawableLef, android:drawableTop, android:drawableRight, android:drawableBottom, android:drawableStart, android:drawableEnd.
<Button
android:id="@+id/button"
android:drawableLeft="@drawable/icon_bus"
android:drawableTop="@drawable/icon_railway"
android:drawableRight="@drawable/icon_car"
android:drawableBottom="@drawable/icon_boat"
android:text="Text"
... />
Android 4.1 started to support text layout differences among different languages. More specifically, in English, text is written from left to right, while in Arabic languages, text is from right to left.
LTR (Left to Right)
In LTR (Left to Right) layout mode: The android:drawableStart attribute will work in the same way as the android:drawableLeft, and the android:drawableEnd will work in the same way as the android:drawableRight.
RTL (Right to Left)
In RTL (Right to Left) layout mode: The android:drawableStart attribute will work in the same way as the android:drawableRight, and android:drawableEnd attribute will work in the same way as the android:drawableStart.
- TODO Link!
Click event happens after the user presses down and releases the Button.
You can define the name of the method which will be called when the user clicks on the Button by using the android.onClick attribute.
<Button
android:id="@+id/button_clickMe"
android:onClick="onClickHandler"
android:text="Click Me"
... />
Simultaneously create this method in MainActivity class.
// MainActivity
public void onClickHandler(View view) {
Toast.makeText(this, "You click on 'Click Me' button!", Toast.LENGTH_SHORT).show();
}
You can define the method that will be called when the user clicks on the Button by Java code:
this.buttonClickMe = (Button) this.findViewById(R.id.button_clickMe);
this.buttonClickMe.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Toast.makeText(MainActivity.this, "You click on 'Click Me' button!", Toast.LENGTH_SHORT).show();
}
});
Long Click events in Android happen when the user presses down and hold the View for a long time. Specifically, the event will happen at the LONG_PRESS_TIMEOUT milliseconds since the user presses it down.You can get the value of the LONG_PRESS_TIMEOUT from the ViewConfiguration.getLongPressTimeout() method.
The default duration of a Long-Click in Android is DEFAULT_LONG_PRESS_TIMEOUT milliseconds. The user can change the Long-Click duration in the Settings of the device, which will be applied for all applications in the system. Application developers are not able to change this value.
| Constant (private) |
Method |
Value
(Milliseconds)
|
| DEFAULT_LONG_PRESS_TIMEOUT | 500 | |
| ViewConfiguration.getLongPressTimeout() | 500 (default) |
For example: Handling the event when the user Long Click in a Button by Java codes (Note that you cannot do this with XML).
this.buttonClickMe = (Button) this.findViewById(R.id.button_clickMe);
this.buttonClickMe.setOnLongClickListener(new View.OnLongClickListener() {
@Override
public boolean onLongClick(View v) {
Toast.makeText(MainActivity.this, "You long click on 'Click Me' button!", Toast.LENGTH_SHORT).show();
return true;
}
});
If the user clicks on View for a long time (longer than LONG_PRESS_TIMEOUT milliseconds), that action can generate two consecutive events, Long-Click and Click.
The onLongClick(View) method returns a boolean value. Returning true means that you have consumed the Long-Click event, and the Click event which happens after that will be ignored. Otherwise, if the onLongClick(View) method returns the false value, it means the Click event which happens after that will be executed.
Here is a simple example: the user will enter two numbers, and click the Button to sum these two numbers.
Design the example interface:
Align the position of components in the interface:
Set ID, and Text for the components in the interface:
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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"
tools:context=".MainActivity">
<TextView
android:id="@+id/textView"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginLeft="16dp"
android:layout_marginTop="16dp"
android:layout_marginEnd="16dp"
android:layout_marginRight="16dp"
android:text="Number 1"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<EditText
android:id="@+id/editText_number1"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginLeft="16dp"
android:layout_marginTop="16dp"
android:layout_marginEnd="16dp"
android:layout_marginRight="16dp"
android:ems="10"
android:inputType="number"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/textView" />
<TextView
android:id="@+id/textView2"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginLeft="16dp"
android:layout_marginTop="16dp"
android:layout_marginEnd="16dp"
android:layout_marginRight="16dp"
android:text="Number 2"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/editText_number1" />
<EditText
android:id="@+id/editText_number2"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginLeft="16dp"
android:layout_marginTop="16dp"
android:layout_marginEnd="16dp"
android:layout_marginRight="16dp"
android:ems="10"
android:inputType="number"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/textView2" />
<Button
android:id="@+id/button_add"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="16dp"
android:text="Add"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/editText_number2" />
</androidx.constraintlayout.widget.ConstraintLayout>
MainActivity.java
package org.o7planning.buttonexample;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.view.ViewConfiguration;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
private EditText editTextNumber1;
private EditText editTextNumber2;
private Button buttonAdd;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
this.editTextNumber1 = (EditText) this.findViewById(R.id.editText_number1);
this.editTextNumber2 = (EditText) this.findViewById(R.id.editText_number2);
this.buttonAdd = (Button) this.findViewById(R.id.button_add);
this.buttonAdd.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
add2Number();
}
});
}
private void add2Number() {
String str1 = this.editTextNumber1.getText().toString();
String str2 = this.editTextNumber2.getText().toString();
try {
double value1 = Double.parseDouble(str1);
double value2 = Double.parseDouble(str2);
double result = value1 + value2;
Toast.makeText(this, "Result: " + result, Toast.LENGTH_SHORT).show();
} catch(Exception e) {
Toast.makeText(this, "Error: "+ e, Toast.LENGTH_SHORT).show();
}
}
}
