In App Keyboard

GeekofiaKeyboard.java

package in.geekofia.baseconverter;

import android.content.Context;
import android.text.TextUtils;
import android.util.AttributeSet;
import android.util.SparseArray;
import android.view.LayoutInflater;
import android.view.View;
import android.view.inputmethod.InputConnection;
import android.widget.LinearLayout;

import com.google.android.material.button.MaterialButton;

public class GeekofiaKeyboard extends LinearLayout implements View.OnClickListener {

    private MaterialButton button1, button2, button3, button4,
            button5, button6, button7, button8,
            button9, button0, buttonDelete, buttonEnter;

    private SparseArray<String> keyValues = new SparseArray<>();
    private InputConnection inputConnection;

    public GeekofiaKeyboard(Context context) {
        this(context, null, 0);
    }

    public GeekofiaKeyboard(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public GeekofiaKeyboard(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context, attrs);
    }

    private void init(Context context, AttributeSet attrs) {
        LayoutInflater.from(context).inflate(R.layout.keyboard, this, true);
        button1 = findViewById(R.id.button_1);
        button1.setOnClickListener(this);
        button2 = findViewById(R.id.button_2);
        button2.setOnClickListener(this);
        button3 = findViewById(R.id.button_3);
        button3.setOnClickListener(this);
        button4 = findViewById(R.id.button_4);
        button4.setOnClickListener(this);
        button5 = findViewById(R.id.button_5);
        button5.setOnClickListener(this);
        button6 = findViewById(R.id.button_6);
        button6.setOnClickListener(this);
        button7 = findViewById(R.id.button_7);
        button7.setOnClickListener(this);
        button8 = findViewById(R.id.button_8);
        button8.setOnClickListener(this);
        button9 = findViewById(R.id.button_9);
        button9.setOnClickListener(this);
        button0 = findViewById(R.id.button_0);
        button0.setOnClickListener(this);
        buttonDelete = findViewById(R.id.button_delete);
        buttonDelete.setOnClickListener(this);
        buttonEnter = findViewById(R.id.button_enter);
        buttonEnter.setOnClickListener(this);

        keyValues.put(R.id.button_1, "1");
        keyValues.put(R.id.button_2, "2");
        keyValues.put(R.id.button_3, "3");
        keyValues.put(R.id.button_4, "4");
        keyValues.put(R.id.button_5, "5");
        keyValues.put(R.id.button_6, "6");
        keyValues.put(R.id.button_7, "7");
        keyValues.put(R.id.button_8, "8");
        keyValues.put(R.id.button_9, "9");
        keyValues.put(R.id.button_0, "0");
        keyValues.put(R.id.button_enter, "\n");
    }

    @Override
    public void onClick(View view) {
        if (inputConnection == null)
            return;

        if (view.getId() == R.id.button_delete) {
            CharSequence selectedText = inputConnection.getSelectedText(0);

            if (TextUtils.isEmpty(selectedText)) {
                inputConnection.deleteSurroundingText(1, 0);
            } else {
                inputConnection.commitText("", 1);
            }
        } else {
            String value = keyValues.get(view.getId());
            inputConnection.commitText(value, 1);
        }
    }

    public void setInputConnection(InputConnection ic) {
        inputConnection = ic;
    }
}

keyboard.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <com.google.android.material.button.MaterialButton
            android:id="@+id/button_1"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            style="@style/Widget.MaterialComponents.Button.TextButton"
            android:text="1" />

        <com.google.android.material.button.MaterialButton
            android:id="@+id/button_2"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            style="@style/Widget.MaterialComponents.Button.TextButton"
            android:text="2" />

        <com.google.android.material.button.MaterialButton
            android:id="@+id/button_3"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            style="@style/Widget.MaterialComponents.Button.TextButton"
            android:layout_weight="1"
            android:text="3" />

        <com.google.android.material.button.MaterialButton
            android:id="@+id/button_4"
            android:layout_width="0dp"
            style="@style/Widget.MaterialComponents.Button.TextButton"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="4" />

        <com.google.android.material.button.MaterialButton
            android:id="@+id/button_5"
            android:layout_width="0dp"
            style="@style/Widget.MaterialComponents.Button.TextButton"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="5" />

        <com.google.android.material.button.MaterialButton
            android:id="@+id/button_6"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            style="@style/Widget.MaterialComponents.Button.TextButton"
            android:text="6" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <com.google.android.material.button.MaterialButton
            android:id="@+id/button_7"
            android:layout_width="0dp"
            style="@style/Widget.MaterialComponents.Button.TextButton"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="7" />

        <com.google.android.material.button.MaterialButton
            android:id="@+id/button_8"
            android:layout_width="0dp"
            style="@style/Widget.MaterialComponents.Button.TextButton"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="8" />

        <com.google.android.material.button.MaterialButton
            android:id="@+id/button_9"
            android:layout_width="0dp"
            style="@style/Widget.MaterialComponents.Button.TextButton"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="9" />

        <com.google.android.material.button.MaterialButton
            android:id="@+id/button_0"
            android:layout_width="0dp"
            style="@style/Widget.MaterialComponents.Button.TextButton"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="0" />

        <com.google.android.material.button.MaterialButton
            android:id="@+id/button_delete"
            android:layout_width="0dp"
            style="@style/Widget.MaterialComponents.Button.TextButton"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            app:icon="@drawable/ic_backspace"/>

    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <com.google.android.material.button.MaterialButton
            android:id="@+id/button_enter"
            android:layout_width="0dp"
            style="@style/Widget.MaterialComponents.Button.TextButton"
            android:layout_height="wrap_content"
            android:layout_weight="3"
            android:text="Enter" />


    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

    </LinearLayout>
</LinearLayout>