[JAVA] How to get values in real time with TextWatcher (Android)

Overview

How to reflect (display) characters in TextView when writing characters with EditText. This can be achieved by using TextWatcher.

Implement TextWatcher (implements)

public class MainActivity extends AppCompatActivity implements TextWatcher{
...
}

Implement TextWatcher in the Activity or Fragment you want to display.

Override (beforeTextChanged / onTextChanged / afterTextChanged)

    @Override
    public void beforeTextChanged(CharSequence s, int start, int count, int after) {
    }

    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count) {
    }

    @Override
    public void afterTextChanged(Editable s) {
    }
}

1.beforeTextChanged(CharSequence s, int start, int count,int after) -Method called just before the string is modified ・ Char Sequence s → The character string currently entered in EditText ・ Int start → Start position of the newly added character string in the character string of s ・ Int count → Total number of changed strings in the s string

2.onTextChanged(CharSequence s, int start, int before, int count) ・ Called when one character is entered ・ Char Sequence s → The character string currently entered in EditText ・ Int start → Start position of the newly added character string in the character string of s ・ Int before → Number of existing strings to be deleted ・ Int count → Number of newly added character strings

3.afterTextChanged(Editable s) -Finally this method is called ・ Editable s → The final modifiable, modified string

You can set before, during, and after character input in real time.

• Override is required for these three methods.

Listener registration

addTextChangedListener(this);

Register the target EditText in the listener.

Sample code

MainActivity.java

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity implements TextWatcher {

    EditText editText;
    TextView textView;
    EditText EditText_OUT;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textView = findViewById(R.id.textView);
        editText = findViewById(R.id.editText);

        EditText_OUT = (EditText) findViewById(R.id.editText);
        //Register listener
        EditText_OUT.addTextChangedListener(this);
    }

    @Override
    public void beforeTextChanged(CharSequence s, int start, int count, int after) {

    }

    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count) {

    }

    @Override
    public void afterTextChanged(Editable s) {
        //Reflect the value entered in TextView in real time
        textView.setText(s);
    }
}

activity.main.xml

<?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"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text=""
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.308" />

    <EditText
        android:id="@+id/editText"
        android:layout_width="284dp"
        android:layout_height="79dp"
        android:layout_marginStart="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginBottom="8dp"
        android:textSize="20dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView"
        app:layout_constraintVertical_bias="0.0" />
</android.support.constraint.ConstraintLayout>