Question

Create an app that stores a set of names. The UI should contain a EditText widget and two Buttons (one for adding a name and one for editing a name).   When the app starts up, the first name of the set is used to initialize the EditText widget. The app uses ViewPager so that the user can swipe left to visit the previous name in the set, or swipe right to visit the next name in the set, similar to how you can swipe left and right through crimes in the Criminal Intent app.

If the user types a new name in the EditText field and clicks the edit button, the name is updated in the app's list of names.

If the user types a new name in the EditText field and clicks the add button, the name is added to the end of the set.

You can store the names in an ArrayList of Strings and use the onCreate() method initialze the list so there is something to display when the app first starts up, if you wish.

Your app will not display a list, and therefore will not use RecyclerView. This is different than CriminalIntent and uses the ViewPager differently.

I am completely stumped and need help creating and finishing program. Spent hours trying to start and got nowhere.

Answer 1

Structure of Project :

MainActivity.java

package com.exmaple.viewpager;


import android.content.Context;
import android.content.SharedPreferences;
import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentPagerAdapter;
import androidx.viewpager.widget.ViewPager;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.Set;

import static com.exmaple.viewpager.MySharedPreference.SHARED_PREF;

public class MainActivity extends AppCompatActivity {

    private ArrayList<String> arrayList = new ArrayList<>();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //Getting set of names stored in shared preference
        SharedPreferences sharedPreferences = getSharedPreferences(SHARED_PREF, Context.MODE_PRIVATE);
        Set<String> set = sharedPreferences.getStringSet("STRING_SET",null);
        if(set==null) { //Shared Preference is empty (First time app open)
            arrayList.add("First Item");
        }
        else { // (Set is not empty)
            arrayList.addAll(set);
        }
        //Initializing viewpager and setting a custom adapter.
        ViewPager viewPager = (ViewPager) findViewById(R.id.viewpager);
        viewPager.setAdapter(new CustomPagerAdapter(this, arrayList));
    }
}

CustomPagerAdapter.java :

package com.exmaple.viewpager;
import android.content.Context;

import android.content.SharedPreferences;
import android.text.TextUtils;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.viewpager.widget.PagerAdapter;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.Set;

import static com.exmaple.viewpager.MySharedPreference.SHARED_PREF;

//Custom Adapter class for Pager
class CustomPagerAdapter extends PagerAdapter {

    private ArrayList<String> arrayList;
    private Context mContext;

    public CustomPagerAdapter(Context context,ArrayList<String> arrayList) {
        this.arrayList = arrayList;
        mContext = context;
    }

    //Initiate Item
    @Override
    public Object instantiateItem(ViewGroup collection, final int position) {
        LayoutInflater inflater = LayoutInflater.from(mContext);
        ViewGroup layout = (ViewGroup) inflater.inflate(R.layout.content_main, collection, false);
        //Getting reference of edit text, add button and remove button from content_main.xml
        final EditText editText = layout.findViewById(R.id.edit_text);
        final Button editBtn = layout.findViewById(R.id.edit_button);
        Button addBtn = layout.findViewById(R.id.add_btn);

        editText.setText(arrayList.get(position).toString()); //Setting first value to edit text

        //Onclick for add button
        addBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if(TextUtils.isEmpty(editText.getText())) { //Edit Text is empty
                    Toast.makeText(mContext, "Please Enter Text.", Toast.LENGTH_SHORT).show();
                    return;
                }
                //Add item to array list and notify that data has been changed.
                    arrayList.add(position,editText.getText().toString());
                    notifyDataSetChanged();
                    saveToSharedPreference(); //Saving to shared preference
                Toast.makeText(mContext, "Item Added.", Toast.LENGTH_SHORT).show();
                }
        });

        //Onclick for edit button
        editBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if(TextUtils.isEmpty(editText.getText())) { //Edit Text is empty
                    Toast.makeText(mContext, "Please Enter Text.", Toast.LENGTH_SHORT).show();
                    return;
                }
                //Removing array list item at this position and adding again at this position (Updating/Editing value)
                arrayList.remove(position);
                arrayList.add(position,editText.getText().toString());
                notifyDataSetChanged();
                saveToSharedPreference(); //Saving to shared preference
                Toast.makeText(mContext, "Item Updated.", Toast.LENGTH_SHORT).show();
            }
        });

        collection.addView(layout);
        return layout;
    }

    // This method save Set of names to SharedPreference so that when app closes added names are remain available
    public void saveToSharedPreference() {
        Set<String> set = new HashSet<String>();
        set.addAll(arrayList);
        SharedPreferences sharedPreferences = mContext.getSharedPreferences(SHARED_PREF,Context.MODE_PRIVATE);
        SharedPreferences.Editor editor = sharedPreferences.edit();
        editor.putStringSet("STRING_SET",set);
        editor.apply();
    }

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

    @Override
    public int getCount() {
        return arrayList.size();
    }

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

    @Override
    public CharSequence getPageTitle(int position) {
        return arrayList.get(position);
    }

    @Override
    public void notifyDataSetChanged() {
        super.notifyDataSetChanged();
    }
}

MySharedPreference.java :

package com.exmaple.viewpager;

public class MySharedPreference {
    public static final String SHARED_PREF = "shared_pref";
}

activity_main.xml :

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <androidx.viewpager.widget.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</RelativeLayout>

content_main.xml :

<?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">

   <EditText
       android:id="@+id/edit_text"
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:textColor="@android:color/black"
       android:layout_margin="10dp"
       android:hint="Enter Text"
       android:padding="6dp"/>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:weightSum="2">
        <Button
            android:id="@+id/edit_button"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:padding="6dp"
            android:background="@color/colorPrimary"
            android:text="Edit Name"
            android:layout_margin="5dp"
            android:textColor="@android:color/white"
            android:layout_weight="1"/>
        <Button
            android:id="@+id/add_btn"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:padding="6dp"
            android:background="@color/colorPrimary"
            android:text="Add Name"
            android:layout_margin="5dp"
            android:textColor="@android:color/white"
            android:layout_weight="1"/>

    </LinearLayout>

</LinearLayout>

build.gradle (Module :app) :

add the following dependency to use viewpager in your project :

implementation 'androidx.viewpager:viewpager:1.0.0'

Sample Output (Screenshots) :

When app launch for the first time the EditText will populate with text "First Item" on onCreate method. if pressed on EDIT NAME Button then item at that position will be change by new name and if click ed on ADD NAME Button then new item will be added at the end of list. more than one item can be added with the same name.