How to use Handler to schedule tasks? A simple Slide Show Example (Updated with androix package)

In this tutorial we will be using Handler, which is a very useful class in Android that allows to display a cool animation and also perform various operations where tasks scheduling is required. It also has many other capabilities but for now we will just concentrate on the task scheduling in a very creative way.

In this example we will be creating a slide show app where the user can see the slide show of photos in forward as well as backward. For forward and backward slide show we have just set a boolean in onUserInteraction() method.

For understanding onUserInteraction() method, just hit this link.

Please note: The images are taken from Pixabay.

-----------------------The xml file's content --------------------------

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#1c6d8d">

    <ImageView
        android:id="@+id/bbd_imgIV"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:src="@drawable/i1"/>

</LinearLayout>

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----------------The Java file's code as follows------------------

package com.app.yourappname;

import android.os.Bundle;
import android.os.Handler;
import android.widget.ImageView;

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;

public class HandlerSlideShowActivity extends AppCompatActivity {

    private boolean forwardSlideShow = true;
    private Handler imgHandler = new Handler();
    private ImageView imgIV;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.handler_slideshow_activity);
        imgIV = findViewById(R.id.bbd_imgIV);
    }

    private Runnable mUpdateTimeTask = new Runnable() {
        int imgs[] = {R.drawable.i0, R.drawable.i1, R.drawable.i2, R.drawable.i3, R.drawable.i4};

        int no = 0;
        public void run() {
            if(forwardSlideShow)
                no++;
            else
                no--;

            if(no>imgs.length-1)
                no = 0;

            if(no<0)
                no = imgs.length-1;

            if(imgIV!=null)
                imgIV.setImageResource(imgs[no]);
            imgHandler.postDelayed(mUpdateTimeTask, ( 2 * 1000)) ;
        }
    };

    @Override
    public void onUserInteraction() {
        super.onUserInteraction();
        if(forwardSlideShow) forwardSlideShow = false;
        else forwardSlideShow = true;
    }

    @Override
    protected void onResume() {
        super.onResume();
        imgHandler.removeCallbacks(mUpdateTimeTask);
        imgHandler.postDelayed(mUpdateTimeTask, 500);
    }
}

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---------------------------- Just declare the Activity name in your Manifest file --------------------

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.app.yourappname">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".HandlerSlideShowActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>