Android Studio点击按钮更换背景图片(照片固定)

Xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:orientation="vertical"
    tools:context="com.example.mybeijing.MainActivity"
    android:weightSum="1">
    <Button
        android:id="@+id/button"
        android:layout_width="100dp"
        android:layout_height="60dp"
        android:text="Button"
        tools:layout_editor_absoluteX="148dp"
        tools:layout_editor_absoluteY="121dp"
        />
    <TextView
        android:id="@+id/textView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@drawable/aa"/>
</LinearLayout>

java
package com.example.mybeijing;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity { 

    Button btn;
    TextView tv;
    int i=0;
    @Override
    protected void onCreate(Bundle savedInstanceState) { 
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        btn = (Button)findViewById(R.id.button);
        tv = (TextView)findViewById(R.id.textView);
        btn.setOnClickListener(new View.OnClickListener() { 
            @Override
            public void onClick(View view) { 
                switch (i) { 
                    case 0:tv.setBackgroundResource(R.drawable.bb);i++;break;
                    case 1:tv.setBackgroundResource(R.drawable.cc);i++;break;
                    case 2:tv.setBackgroundResource(R.drawable.dd);i++;break;
                    case 3:tv.setBackgroundResource(R.drawable.ee);i++;break;
                    case 4:tv.setBackgroundResource(R.drawable.ff);i++;break;
                }
                if(i>=5)
                    i=0;
            }
        });
    }
}