Plate keyboard layout

KeyboardPlate.java

package com.example.policante.meuapptest;

import android.os.Bundle;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.GridLayout;
import android.widget.TextView;

public class KeyboardPlate extends AppCompatActivity {

    private static final int MAX_CHARACTER = 7;

    private GridLayout gridLetters;
    private GridLayout gridNumbers;

    private TextView plate;
    private String strPlate = "";

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

        gridLetters = (GridLayout) findViewById(R.id.grid_keyboard_letters);
        gridNumbers = (GridLayout) findViewById(R.id.grid_keyboard_numbers);

        plate = (TextView) findViewById(R.id.plate);

        setClickButtons(gridLetters);
        setClickButtons(gridNumbers);

        findViewById(R.id.btn_clear).setOnClickListener(new View.OnClickListener() {
            @Override public void onClick(View v) {
                updateText(null);
            }
        });

        updateText("");
    }

    private void setClickButtons(GridLayout grid) {
        int childCount = grid.getChildCount();

        for (int i = 0; i < childCount; i++) {
            Button bt = (Button) grid.getChildAt(i);
            bt.setOnClickListener(new View.OnClickListener() {
                public void onClick(View view) {
                    if (view instanceof Button) {
                        String chr = ((Button) view).getText().toString();
                        updateText(chr);
                    }
                }
            });
        }
    }

    private void updateText(String value) {
        if (value != null) {

            if (strPlate.length() >= MAX_CHARACTER) {
                return;
            }

            strPlate += value;
        } else {
            if (strPlate.length() > 0) {
                strPlate = strPlate.substring(0, strPlate.length() - 1);
            }
        }
        plate.setText(strPlate);
        updateKeyboard();
    }

    private void updateKeyboard() {
        if (strPlate.length() < 3) {
            gridLetters.setVisibility(View.VISIBLE);
            gridNumbers.setVisibility(View.GONE);
        } else {
            gridLetters.setVisibility(View.GONE);
            gridNumbers.setVisibility(View.VISIBLE);
        }

        if (strPlate.length() == MAX_CHARACTER) {
            new AlertDialog.Builder(this).setMessage("Plate: " + strPlate).setNeutralButton("OK", null).show();
        }
    }

}

layout_keyboard_plate.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.policante.meuapptest.KeyboardPlate">

    <TextView
        android:id="@+id/plate"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        android:gravity="center"
        android:textSize="22sp"
        android:textStyle="bold"/>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:orientation="vertical"
        android:layout_below="@+id/plate"
        android:layout_above="@+id/btn_clear">

        <GridLayout
            android:id="@+id/grid_keyboard_letters"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:columnCount="4"
            android:orientation="horizontal"
            android:visibility="visible">

            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="A"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="B"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="C"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="D"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="E"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="F"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="G"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="H"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="I"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="J"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="K"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="L"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="M"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="N"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="O"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="P"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="Q"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="R"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="S"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="T"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="U"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="V"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="X"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="W"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="Y"
                android:textSize="20sp"/>
            <Button
                android:layout_width="80dp"
                android:layout_height="60dp"
                android:text="Z"
                android:textSize="20sp"/>

        </GridLayout>

        <GridLayout
            android:id="@+id/grid_keyboard_numbers"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:columnCount="3"
            android:orientation="horizontal"
            android:visibility="gone">

            <Button
                android:layout_width="100dp"
                android:layout_height="70dp"
                android:text="1"
                android:textSize="20sp"/>
            <Button
                android:layout_width="100dp"
                android:layout_height="70dp"
                android:text="2"
                android:textSize="20sp"/>
            <Button
                android:layout_width="100dp"
                android:layout_height="70dp"
                android:text="3"
                android:textSize="20sp"/>
            <Button
                android:layout_width="100dp"
                android:layout_height="70dp"
                android:text="4"
                android:textSize="20sp"/>
            <Button
                android:layout_width="100dp"
                android:layout_height="70dp"
                android:text="5"
                android:textSize="20sp"/>
            <Button
                android:layout_width="100dp"
                android:layout_height="70dp"
                android:text="6"
                android:textSize="20sp"/>
            <Button
                android:layout_width="100dp"
                android:layout_height="70dp"
                android:text="7"
                android:textSize="20sp"/>
            <Button
                android:layout_width="100dp"
                android:layout_height="70dp"
                android:text="8"
                android:textSize="20sp"/>
            <Button
                android:layout_width="100dp"
                android:layout_height="70dp"
                android:text="9"
                android:textSize="20sp"/>
            <Button
                android:layout_width="100dp"
                android:layout_height="70dp"
                android:text="0"
                android:textSize="20sp"/>

        </GridLayout>


    </LinearLayout>


    <Button
        android:id="@+id/btn_clear"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:layout_alignParentBottom="true"
        android:text="limpar"/>

</RelativeLayout>