Android ViewPager Example Tutorial

Android ViewPager widget is found in the support library and it allows the user to swipe left or right to see an entirely new screen. Today we’re implementing a ViewPager by using Views and PagerAdapter. Though we can implement the same using Fragments too, but we’ll discuss that in a later tutorial. The ViewPager uses a PagerAdapter whose job is to supply views to the MainActivity similar to what a ListAdapter does for a ListView.

Android ViewPager Example

Android ViewPager Example Code

The activity_main.xml consists solely of the ViewPager as shown below. activity_main.xml

<RelativeLayout xmlns:android="https://schemas.android.com/apk/res/android"
    xmlns:tools="https://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</RelativeLayout>

The MainActivity.java is given below. MainActivity.java

package com.journaldev.viewpager;

import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;

public class MainActivity extends AppCompatActivity {

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

        ViewPager viewPager = (ViewPager) findViewById(R.id.viewpager);
        viewPager.setAdapter(new CustomPagerAdapter(this));
    }
}

The role of the MainActivity in the above code is to just reference the ViewPager and set the CustomPagerAdapter that extends the PagerAdapter. Before we discuss the CustomPagerAdapter class, let’s look into the ModelObject class. ModelObject.java

package com.journaldev.viewpager;

public enum ModelObject {

    RED(R.string.red, R.layout.view_red),
    BLUE(R.string.blue, R.layout.view_blue),
    GREEN(R.string.green, R.layout.view_green);

    private int mTitleResId;
    private int mLayoutResId;

    ModelObject(int titleResId, int layoutResId) {
        mTitleResId = titleResId;
        mLayoutResId = layoutResId;
    }

    public int getTitleResId() {
        return mTitleResId;
    }

    public int getLayoutResId() {
        return mLayoutResId;
    }

}

The enum above lists all the pages of the ViewPagers. There are three pages with their respective layouts. The layout of a single page is given below. view_blue.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="https://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:background="@android:color/holo_blue_dark"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Second View"
        android:layout_gravity="center_horizontal"
        android:textSize="28sp"
        android:textColor="@android:color/black"
        android:textStyle="bold"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true"
        android:id="@+id/textView" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Swipe left to\nFirst View"
        android:layout_gravity="center_horizontal"
        android:textSize="20sp"
        android:textColor="@android:color/black"
        android:textStyle="bold"
        android:minLines="2"
        android:id="@+id/textView2"
        android:padding="@dimen/activity_horizontal_margin"
        android:layout_alignParentBottom="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Swipe right to\nThird View"
        android:layout_gravity="center_horizontal"
        android:textSize="20sp"
        android:textColor="@android:color/black"
        android:textStyle="bold"
        android:padding="@dimen/activity_horizontal_margin"
        android:minLines="2"
        android:id="@+id/textView3"
        android:layout_alignTop="@+id/textView2"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true" />

</RelativeLayout>

The remaining two pages have similar layouts and are given in the source code of this project. CustomPagerAdapter.java

package com.journaldev.viewpager;

import android.content.Context;
import android.support.v4.view.PagerAdapter;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class CustomPagerAdapter extends PagerAdapter {

    private Context mContext;

    public CustomPagerAdapter(Context context) {
        mContext = context;
    }

    @Override
    public Object instantiateItem(ViewGroup collection, int position) {
        ModelObject modelObject = ModelObject.values()[position];
        LayoutInflater inflater = LayoutInflater.from(mContext);
        ViewGroup layout = (ViewGroup) inflater.inflate(modelObject.getLayoutResId(), collection, false);
        collection.addView(layout);
        return layout;
    }

    @Override
    public void destroyItem(ViewGroup collection, int position, Object view) {
        collection.removeView((View) view);
    }

    @Override
    public int getCount() {
        return ModelObject.values().length;
    }

    @Override
    public boolean isViewFromObject(View view, Object object) {
        return view == object;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        ModelObject customPagerEnum = ModelObject.values()[position];
        return mContext.getString(customPagerEnum.getTitleResId());
    }

}

1. CustomPagerAdapter(Context context) : The constructor needs a Context reference. The context is saved as a member variable of the class since it’s used later to access the individual page layouts from the enum class
2. instantiateItem : In this case, we use the enum and inflate the particular enum value’s associated layout. Then, we add the newly inflated layout to the ViewGroup(collection of Views) maintained by the PagerAdapter, and then we return that layout. The object being returned by this method is also used later on, as the second parameter in the isViewFromObject method
3. destroyItem : This method removes a particular view from the ViewGroup maintained by the PagerAdapter
4. getCount : It simply returns the number of views that will be maintained by the ViewPager. For this example, the count is the number of enum values in the model object
5. isViewFromObject : This method checks whether a particular object belongs to a given position, which is made simple. As noted earlier, the second parameter is of type Object and is the same as the return value from the instantiateItem method
6. getPageTitle : At a given position, we need to supply the PagerAdapter with a title. This usually manifests itself in the ActionBar as the Activity’s title, or sometimes tabs will hook into this method for labelling each tab. In this case we’ve kept it for labelling only

The image below shows the app in action. This brings an end to ViewPager in android example tutorial. You can download the Android ViewPager Project from the below link.

Download Android ViewPager Example Project