how to pick a random image from the DCIM directory to set it as wallpaper?

I have a problem with picking randomly an image from the DCIM directory.

Here is my code (in MainActivity.java):

public class MainActivity extends AppCompatActivity {

    Random ran;

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

                String secStore = System.getenv("SECONDARY_STORAGE");
                File imagedir = new File(secStore + "/DCIM");
                int totalNumFiles = imagedir.listFiles().length;   //nb of files in DCIM
                //we pick up one randomly
                ran = new Random();
                int indice = ran.nextInt(totalNumFiles) + 1;

                Bitmap bitmap = imagedir[indice];
                WallpaperManager manager = WallpaperManager.getInstance(getApplicationContext());
                manager.setBitmap(bitmap);
//              Toast.makeText(context, "WP set!", Toast.LENGTH_SHORT).show();
    }

}

and in the manifest, I have declared:

<uses-permission android:name="android.permission.SET_WALLPAPER"/>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

The activity_main.xml has nothing on it.

My problem:

Bitmap bitmap = imagedir[indice];

I can't succeed to make the bridge between the random and the bitmap.

Anybody has an idea?

So, it works now and I have found a solution to my two problems:

• minSDK API23 to API22:
  the simplest was to recreate a totally new project with the right minSDK API22 from scratch to get rid of that point. Java indicates then that getExternalStoragePublicDirectory is deprecated but the code below fully works.

• right code:
  Here it is:

package com.example.randomwallpaper;

import androidx.appcompat.app.AppCompatActivity;
import android.app.WallpaperManager;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.os.Environment;
import android.widget.Toast;
import java.io.File;
import java.io.IOException;
import java.util.Random;

import static android.os.Environment.getExternalStoragePublicDirectory;

public class MainActivity extends AppCompatActivity {

    Random ran;

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

        String secStore = System.getenv("SECONDARY_STORAGE");
        File imagedir = getExternalStoragePublicDirectory(Environment.DIRECTORY_DCIM);
        int totalNumFiles = imagedir.listFiles().length;   //nb of files in DCIM
        //we pick up one randomly
        ran = new Random();
        int indice = ran.nextInt(totalNumFiles) + 1;

        Bitmap bitmap = BitmapFactory.decodeFile(String.valueOf(imagedir.listFiles()[indice]));
        WallpaperManager manager = WallpaperManager.getInstance(getApplicationContext());
        try {
            manager.setBitmap(bitmap);
            Toast.makeText(getApplicationContext(), "WP set!", Toast.LENGTH_SHORT).show();
        } catch (IOException e) {
            Toast.makeText(getApplicationContext(), "Error!", Toast.LENGTH_SHORT).show();
        }
    }
}

Each time you launch the app, the wallpaper is randomly changed. The images are stored in the DCIM directory. There are only images and no subdirectory in the DCIM directory. Don't forget to declare the user's permissions in the manifest.