My xml

package com.example.i310_54.myapplication08;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.CountDownTimer;
import android.os.Handler;
import android.os.Message;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.ProgressBar;

import java.util.Random;

class Tiger extends View {
    int flag = 0;

    public Tiger(Context context) {
        super(context);
    }

    public Tiger(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }

    public Tiger(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        Paint paint = new Paint();
        paint.setColor(Color.RED);

        canvas.drawRect(10 - flag, 20 - flag, 30 + flag, 40 + flag, paint);

    }
    void inC(){
        flag+=20;
        invalidate();

    }
    void deC(){
        flag-=20;
        invalidate();
    }

}

public class MainActivity extends AppCompatActivity {

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

    public void f1(View view) {
        Tiger tiger = findViewById(R.id.cv);
        tiger.inC();

    }

    public void f2(View view) {
        Tiger tiger = findViewById(R.id.cv);
        tiger.deC();

    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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="com.example.i310_54.myapplication08.MainActivity"
    android:orientation="vertical"
    android:weightSum="1"
    >


    <com.example.i310_54.myapplication08.Tiger
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="0.5"
        android:id="@+id/cv"
         />

    <Button
        android:id="@+id/b"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="UPSIZING"
        android:onClick="f1"
        />
    <Button
        android:id="@+id/b2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="downSizing"
        android:onClick="f2"
        />

</LinearLayout>