Android RecyclerView Pagination – Next/Previous Pagination

Android RecyclerView Pagination – Next/Previous Pagination

In this class we see how to page/paginate data which is very important especially with RecyclerView which are meant to show large datasets.

The type of pagination we do here is the next/previous pagination. The user can navigate pages via the next/previous buttons.

If we reach the last page the next button gets disabled automatically while if we are at the first page the previous button gets disabled. In between both buttons are enabled.

Why Pagination?

Pagination is vital for not only ease of use by the user but also for smooth perfomance of the device. Users need permission because we human beings are not very good at processing huge data sets. It overwhelms when we have to scroll through a large list of data and identify an item out of it. Instead our brain is good ta getting the gist of things. Just a snapshot so that we have the big picture.

It’s why I always encourage through my tutorials adding of search as well as pagination to lists of data. Pagination allows user to break data into chunks. Users can then view a small amount at a time. Maybe 5 or 10 items.

Pagination also improves the loading time of data. Especially when data is coming from a data source like a database or cloud solutions like firebase. This is important because the android OS is very strict with resource usages in applications. So when your app has a large data set that it’ loading and this takes time, the android OS may shut down you activity due to too much memory usage. This lead to bad reputation and negative reviews in the play store and online review sites.

Paging data enables user move along the workflow quickly and efficiently.

Next/Previous Pagination

There are several pagination types like load more, 1,2,3… and endless pagination. However next/previous is the oldest of these and applies to most systems and frameworks. You basically have two buttons, one is next and the other is previous. Next allows you navigate to the next page while previous allows you navigate to previous page.

Let’s go.

1. Create Basic Activity Project

1. First create a new project in android studio. Go to File –> New Project.

Here’s our project struecture.

2. Build.gradle

Let’s come to our app level(app folder) build.gradle:

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    testImplementation 'junit:junit:4.12'
    implementation 'com.android.support:appcompat-v7:24.2.0'
    implementation 'com.android.support:design:24.2.0'
    implementation 'com.android.support:cardview-v7:24.2.0'

}

You can see from our build.gradle that we aren’t using any third party libraries. Instead we have appcompat, design and cardview support libraries. We are interested in the design support as it has the recyclerview which is the list component we use. The appcompat on the other had will give us the AppCompatActivity which is our MainActivity's super class. Our recyclerview will be showing cardviews.

3. Create User Interface

User interfaces are typically created in android using XML layouts as opposed to direct java coding.

Here are our layouts for this project:

(a). activity_main.xml

• This layout gets inflated to MainActivity user interface.
• It includes the content_main.xml.

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout 
    
    
    android_layout_width="match_parent"
    android_layout_height="match_parent"
    android_fitsSystemWindows="true"
    tools_context="com.tutorials.hp.recyclerpagination.MainActivity">

    <android.support.design.widget.AppBarLayout
        android_layout_width="match_parent"
        android_layout_height="wrap_content"
        android_theme="@style/AppTheme.AppBarOverlay">

        <android.support.v7.widget.Toolbar
            android_id="@+id/toolbar"
            android_layout_width="match_parent"
            android_layout_height="?attr/actionBarSize"
            android_background="?attr/colorPrimary"
            app_popupTheme="@style/AppTheme.PopupOverlay" />

    </android.support.design.widget.AppBarLayout>

    <include layout="@layout/content_main" />

    <android.support.design.widget.FloatingActionButton
        android_id="@+id/fab"
        android_layout_width="wrap_content"
        android_layout_height="wrap_content"
        android_layout_gravity="bottom|end"
        android_layout_margin="@dimen/fab_margin"
        android_src="@android:drawable/ic_dialog_email" />

</android.support.design.widget.CoordinatorLayout>

(b). content_main.xml

This layout gets included in your activity_main.xml.
We define our UI widgets here.

In this case we add a RecyclerView and two buttons(next/previous). At the root we have defined a RelativeLayout.

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 
    
    
    android_layout_width="match_parent"
    android_layout_height="match_parent"
    android_paddingBottom="@dimen/activity_vertical_margin"
    android_paddingLeft="@dimen/activity_horizontal_margin"
    android_paddingRight="@dimen/activity_horizontal_margin"
    android_paddingTop="@dimen/activity_vertical_margin"
    app_layout_behavior="@string/appbar_scrolling_view_behavior"
    tools_context="com.tutorials.hp.recyclerpagination.MainActivity"
    tools_showIn="@layout/activity_main">

    <LinearLayout
        android_orientation="vertical"
        android_layout_width="match_parent"
        android_layout_height="wrap_content">

        <android.support.v7.widget.RecyclerView
            android_id="@+id/rv"
            android_layout_width="match_parent"
            android_layout_height="wrap_content"
            />

        <LinearLayout
            android_orientation="horizontal"
            android_layout_width="wrap_content"
            android_layout_height="wrap_content">
            <Button
                android_text="Previous"
                android_id="@+id/prevBtn"
                android_layout_width="wrap_content"
                android_layout_height="wrap_content" />
            <Button
                android_text="Next"
                android_id="@+id/nextBtn"
                android_layout_width="wrap_content"
                android_layout_height="wrap_content" />
        </LinearLayout>

    </LinearLayout>
</RelativeLayout>

We have two LinearLayouts. The second one will render our next and previous buttons next to each other horizontally. That’s why it’s orientation is horizontal. The first one will place our recyclerview above the two buttons, that’s why we’ve set the orientation to vertical.

(c). model.xml

This is the layout that defines the model of a single CardView in our RecyclerView. So we start by defining the CardView as the root view. We’ve given it several properties like the Card corner radius and card elevation. We have a TextView inside it. That textview will be used to render our data.

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView 
    android_orientation="horizontal" android_layout_width="match_parent"
    
    android_layout_margin="5dp"
    card_view_cardCornerRadius="5dp"
    card_view_cardElevation="2dp"
    android_layout_height="130dp">

    <RelativeLayout
        android_layout_width="match_parent"
        android_layout_height="match_parent">

        <TextView
            android_layout_width="wrap_content"
            android_layout_height="wrap_content"
            android_textAppearance="?android:attr/textAppearanceLarge"
            android_text="Name"
            android_id="@+id/nameTxt"
            android_padding="10dp"
            android_layout_alignParentLeft="true"
             />
    </RelativeLayout>
</android.support.v7.widget.CardView>

Lets now come to classes:

4. MyViewHolder.java

This is our RecyclerView.ViewHolder class:

This class in our RecyclerView.ViewHolder class.

It derives from android.support.v7.widget.RecyclerView.View thus forcing us to create a constructor public MyHolder(View itemView) that takes a View object as a parameter and pass it over the base clas by a call to super(itemView).

Here are the roles of this class

Here’s the ViewHolder code.

package com.tutorials.hp.recyclerpagination.mRecycler;

import android.support.v7.widget.RecyclerView;
import android.view.View;
import android.widget.TextView;

import com.tutorials.hp.recyclerpagination.R;

public class MyViewHolder extends RecyclerView.ViewHolder {

        TextView nametxt;

        public MyViewHolder(View itemView) {
            super(itemView);
            nametxt= (TextView) itemView.findViewById(R.id.nameTxt);
        }
}

4. MyAdapter.java

This is our RecyclerView.Adapter class.

This is our RecyclerView.Adapter class.

It derives from android.support.v7.widget.RecyclerView.Adapter<RecyclerView.ViewHolder myHolder> class.

Deriving from Recylcerview.Adapter will force us to either make our adapter class abstract or go ahead and override a couple of methods. We choose the latter, overriding onCreateViewHolder(ViewGroup parent, int viewType) and onBindViewHolder(MyHolder holder, final int position).

This class will adapt our data set to our RecyclerView which we use an adapterview adapterview.

Here are the main responsibilities of this class:

package com.tutorials.hp.recyclerpagination.mRecycler;

import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Toast;

import com.tutorials.hp.recyclerpagination.R;

import java.util.ArrayList;

public class MyAdapter extends RecyclerView.Adapter<MyViewHolder>  {
    Context c;
    ArrayList<String> spacecrafts;
    public MyAdapter(Context c, ArrayList<String> spacecrafts) {
        this.c = c;
        this.spacecrafts = spacecrafts;
    }

    //INITIALIZE VH
    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View v= LayoutInflater.from(parent.getContext()).inflate(R.layout.model,parent,false);
        return new MyViewHolder(v);
    }
    @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {
        //BIND DATA
        holder.nametxt.setText(spacecrafts.get(position));
    }
    //TOTAL NUM
    @Override
    public int getItemCount() {
        return spacecrafts.size();
    }
}

6. Paginator.java

This is the class that will page/paginate our RecyclerView data.

package com.tutorials.hp.recyclerpagination.mPager;

import java.util.ArrayList;

public class Paginator {
    public static final int TOTAL_NUM_ITEMS=52;
    public static final int ITEMS_PER_PAGE=7;
    public static final int ITEMS_REMAINING=TOTAL_NUM_ITEMS % ITEMS_PER_PAGE;
    public static final int LAST_PAGE=TOTAL_NUM_ITEMS/ITEMS_PER_PAGE;

    public ArrayList<String> generatePage(int currentPage)
    {
        int startItem=currentPage*ITEMS_PER_PAGE+1;
        int numOfData=ITEMS_PER_PAGE;
        ArrayList<String> pageData=new ArrayList<>();

        if (currentPage==LAST_PAGE && ITEMS_REMAINING>0)
        {
            for (int i=startItem;i<startItem+ITEMS_REMAINING;i++)
            {
                pageData.add("Number "+i);
            }
        }else
        {
            for (int i=startItem;i<startItem+numOfData;i++)
            {
                pageData.add("Number "+i);
            }
        }
        return pageData;
    }
}

7. MainActivity.java

So this is our main activity. It derives from AppCompatActivity.

Here are it’s major responsibilities:

package com.tutorials.hp.recyclerpagination;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.widget.Button;

import com.tutorials.hp.recyclerpagination.mPager.Paginator;
import com.tutorials.hp.recyclerpagination.mRecycler.MyAdapter;

public class MainActivity extends AppCompatActivity {

    RecyclerView rv;
    Button nextBtn, prevBtn;
    Paginator p = new Paginator();
    private int totalPages = Paginator.TOTAL_NUM_ITEMS / Paginator.ITEMS_PER_PAGE;
    private int currentPage = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        //RFERENCE VIEWS
        rv = (RecyclerView) findViewById(R.id.rv);
        nextBtn = (Button) findViewById(R.id.nextBtn);
        prevBtn = (Button) findViewById(R.id.prevBtn);
        prevBtn.setEnabled(false);

        //RECYCLER PROPERTIES
        rv.setLayoutManager(new LinearLayoutManager(this));

        //ADAPTER
        rv.setAdapter(new MyAdapter(MainActivity.this, p.generatePage(currentPage)));

        //NAVIGATE
        nextBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                currentPage += 1;
                // enableDisableButtons();
                rv.setAdapter(new MyAdapter(MainActivity.this, p.generatePage(currentPage)));
                toggleButtons();

            }
        });
        prevBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                currentPage -= 1;

                rv.setAdapter(new MyAdapter(MainActivity.this, p.generatePage(currentPage)));

                toggleButtons();
            }
        });
    }

    private void toggleButtons() {
        if (currentPage == totalPages) {
            nextBtn.setEnabled(false);
            prevBtn.setEnabled(true);
        } else if (currentPage == 0) {
            prevBtn.setEnabled(false);
            nextBtn.setEnabled(true);
        } else if (currentPage >= 1 && currentPage <= totalPages) {
            nextBtn.setEnabled(true);
            prevBtn.setEnabled(true);
        }
    }
}

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