Activity.java

package pl.selvin.wallpaperchanger;

import android.app.AlarmManager;
import android.app.IntentService;
import android.app.PendingIntent;
import android.app.WallpaperManager;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import java.io.InputStream;
import java.net.URL;


public class Activity extends android.app.Activity {
    final static String TAG = "AllInOne";
    final static int CHANGE_INTERVAL = 30 * 1000; //30 sec for testing
    static boolean loading = false;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        PendingIntent pending = PendingIntent.getBroadcast(this, 666, new Intent("pl.selvin.wallpaperchanger.CHANGE_WALLPAPTER_TIMER"), PendingIntent.FLAG_CANCEL_CURRENT);
        ((AlarmManager) getSystemService(Context.ALARM_SERVICE)).setRepeating(AlarmManager.RTC_WAKEUP, System.currentTimeMillis(), CHANGE_INTERVAL, pending);
    }

    public static class Service extends IntentService {
        public Service() {
            super("wallpaperchanger-download");
        }

        @Override
        protected void onHandleIntent(Intent intent) {
            WallpaperManager wm = WallpaperManager.getInstance(this);
            int height = wm.getDesiredMinimumHeight();
            int width = wm.getDesiredMinimumWidth();
            String url = "https://source.unsplash.com/category/nature/" + width + "x" + height + "/";
            try {
                InputStream input = new URL(url).openStream();
                Log.v(TAG, url);
                wm.setStream(input);
                input.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
            loading = false;
        }
    }

    public static class AlarmReceiver extends BroadcastReceiver {
        @Override
        public void onReceive(final Context context, Intent intent) {
            if (!loading) {
                loading = true;
                context.startService(new Intent(context, Service.class));
            }
        }
    }
}

AndroidManifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="pl.selvin.wallpaperchanger">

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

    <application
        android:allowBackup="true"
        android:label="WallpaperChanger">
        <activity
            android:name=".Activity"
            android:label="WallpaperChanger">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <receiver android:name=".Activity$AlarmReceiver">
            <intent-filter>
                <action android:name="pl.selvin.wallpaperchanger.CHANGE_WALLPAPTER_TIMER" />
            </intent-filter>
        </receiver>
        <service android:name=".Activity$Service" />
    </application>

</manifest>

build.gradle

apply plugin: 'com.android.application'

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.2"

    defaultConfig {
        applicationId "pl.selvin.wallpaperchanger"
        minSdkVersion 5
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt')
        }
    }
}

dependencies {
}

LICENSE

Copyright Selvin

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.