Case Study :

Working with an E-Commerce application, I was asked to implement a custom date/time picker for delivery time slot as below.

Being a lazy developer, my first approach was to look for a library that would make my work a lot easier. And after few (actually many) Google searches, I decided to use AigeStudio’s WheelPicker library.

And where things started to go wrong?

• Our UI slightly changed and we were having different formats of time for API response and App UI (they were very different). So I had to use a more complex Object model for Collection.
• Since, There were two WheelPickers in the UI and the data in second one was entirely dependent upon that in first one. There were a lot of issues with changing data.

As Solution to first problem, one can simply override the toString() function and return the required date/time format.

But, In second case there were a lot of issues with changing data. The library provides a single setData() method which in most cases didn’t worked well for us. setSelectedItemPosition() wasn’t working either in few cases.

And then I just get to know of SnapHelper in RecyclerView.

SnapHelper

SnapHelper is the utility class that help to implement snapping in RecyclerView. Support library 24.2.0 introduced two helper classes SnapHelper and LinearSnapHelper for handling snapping in RecyclerView.

Github Project

Making List

activity_main.xml

MainActivity XML Layout

<?xml version="1.0" encoding="utf-8"?>

<android.support.v7.widget.LinearLayoutCompat     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"     android:orientation="vertical"     tools:context="com.github.angads25.androidwheel.MainActivity">

    <android.support.v7.widget.AppCompatTextView         android:id="@+id/tv_date"         android:layout_width="match_parent"         android:layout_height="?android:attr/listPreferredItemHeightSmall"         android:gravity="center"         android:textSize="18sp"         android:textStyle="bold"         tools:text="@string/app_name"/>

    <android.support.v7.widget.RecyclerView         android:id="@+id/date_picker"         android:layout_width="match_parent"         android:layout_height="wrap_content"         android:background="#000000"         android:foreground="@drawable/shape_picker_shade"         tools:listitem="@layout/list_item_date_time"/>

</android.support.v7.widget.LinearLayoutCompat>

DateBean.java

Pojo for Date

package com.github.angads25.androidwheel;

/**

 *

 * Created by Angad Singh on 26/11/17.

 *

 */

public class DateBean {

    private String date;

    private long timeStamp;

    public String getDate() {

        return date;

    }

    public void setDate(String date) {

        this.date = date;

    }

    public long getTimeStamp() {

        return timeStamp;

    }

    public void setTimeStamp(long timeStamp) {

        this.timeStamp = timeStamp;

    }

}

list_item_date_time.xml

RecyclerView list item

<?xml version="1.0" encoding="utf-8"?>

<FrameLayout     xmlns:android="http://schemas.android.com/apk/res/android"     xmlns:tools="http://schemas.android.com/tools"     android:layout_width="match_parent"     android:layout_height="?android:attr/listPreferredItemHeight"     android:background="#333333">

    <android.support.v7.widget.AppCompatTextView         android:id="@+id/tv_data"         android:layout_width="match_parent"         android:layout_height="wrap_content"         android:gravity="center"         android:textSize="16sp"         android:layout_gravity="center_vertical"         android:layout_marginLeft="16dp"         android:layout_marginStart="16dp"         android:layout_marginRight="16dp"         android:layout_marginEnd="16dp"         android:textColor="#FFFFFF"         tools:text="@string/app_name"/>

</FrameLayout>

PickerAdapter.java

Adapter class for RecyclerView

package com.github.angads25.androidwheel;

 

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

import java.util.ArrayList;

 

/**
*
* Created by Angad Singh on 22/11/17.
*
*/

 

public class PickerAdapter extends RecyclerView.Adapter {
private Context context;
private ArrayList strings;

public PickerAdapter(Context context, ArrayList strings) {
this.context = context;
this.strings = strings;
}

@Override
public PickerViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(context).inflate(R.layout.list_item_date_time, parent, false);
return new PickerViewHolder(view);
}

@Override
public void onBindViewHolder(PickerViewHolder holder, int position) {
holder.tvData.setText(strings.get(position).getDate());
}

@Override
public int getItemCount() {
return strings.size();
}

class PickerViewHolder extends RecyclerView.ViewHolder {
private AppCompatTextView tvData;

PickerViewHolder(View itemView) {
super(itemView);
tvData = itemView.findViewById(R.id.tv_data);
}
}
}

Making RecyclerView Snap Center Item

MainActivity.java

package com.github.angads25.androidwheel;

import android.os.Bundle;

import android.support.v7.app.AppCompatActivity;

import android.support.v7.widget.AppCompatTextView;

import android.support.v7.widget.LinearLayoutCompat;

import android.support.v7.widget.LinearLayoutManager;

import android.support.v7.widget.LinearSnapHelper;

import android.support.v7.widget.RecyclerView;

import android.util.TypedValue;

import android.view.View;

import android.widget.AbsListView;

import java.util.ArrayList;

import java.util.Calendar;

public class MainActivity extends AppCompatActivity {

    private String[] months = {

            "Jan", "Feb", "Mar",

            "Apr", "May", "Jun",

            "Jul", "Aug", "Sep",

            "Oct", "Nov", "Dec"

    };

    private AppCompatTextView dateTv;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        // Maximum visible items in WheelPicker as a time.

        int maxItems = 3;

        // We will adjust height of recyclerView to fit

        // exactly maximum visible items.

        int recyclerViewHeight = 0;

        TypedValue tv = new TypedValue();

        if (getTheme().resolveAttribute(android.R.attr.listPreferredItemHeight, tv, true)) {

            // Calculating recyclerView height from listItemHeight

            // we are using in our recyclerView list item.

            recyclerViewHeight = maxItems * TypedValue.complexToDimensionPixelSize(tv.data, getResources().getDisplayMetrics());

        }

        dateTv = findViewById(R.id.tv_date);

        final RecyclerView dateList = findViewById(R.id.date_picker);

        LinearLayoutCompat.LayoutParams dateParams = (LinearLayoutCompat.LayoutParams) dateList.getLayoutParams();

        dateParams.height = recyclerViewHeight;

        dateList.setLayoutParams(dateParams);

        final ArrayList<DateBean> arrayList = new ArrayList<>();

        // Adding blank field in beginning of list so that

        // first date item is selectable.

        DateBean padding = new DateBean();

        padding.setDate("");

        arrayList.add(padding);

        // Adding 7 consecutive days to date picker.

        Calendar calendar = Calendar.getInstance();

        for(int i = 0; i < 7; i++) {

            DateBean date = new DateBean();

            date.setDate(

                    months[calendar.get(Calendar.MONTH)] + " " +

                    calendar.get(Calendar.DAY_OF_MONTH) + ", " +

                    calendar.get(Calendar.YEAR));

            date.setTimeStamp(calendar.getTimeInMillis());

            arrayList.add(date);

            calendar.add(Calendar.DAY_OF_MONTH, 1);

        }

        // Adding blank field in last so that last item is

        // selectable.

        arrayList.add(padding);

        PickerAdapter adapter = new PickerAdapter(MainActivity.this, arrayList);

        final LinearLayoutManager manager = new LinearLayoutManager(

                MainActivity.this,

                LinearLayoutManager.VERTICAL,

                false);

        final LinearSnapHelper snapHelper = new LinearSnapHelper();

        // Attaching SnapHelper to recyclerView.

        snapHelper.attachToRecyclerView(dateList);

        // Setting layout manager to recyclerView.

        dateList.setLayoutManager(manager);

        //

        dateList.setOnFlingListener(snapHelper);

        // Setting adapter to recyclerView.

        dateList.setAdapter(adapter);

        // Listening to scroll events on RecyclerView.

        dateList.addOnScrollListener(new RecyclerView.OnScrollListener() {

            @Override

            public void onScrollStateChanged(RecyclerView recyclerView, int newState) {

                super.onScrollStateChanged(recyclerView, newState);

                if(newState == AbsListView.OnScrollListener.SCROLL_STATE_IDLE) {

                    View centerView = snapHelper.findSnapView(manager);

                    // Getting position of the center/snapped item.

                    int pos = manager.getPosition(centerView);

                    dateTv.setText(arrayList.get(pos).getDate());

                }

            }

        });

    }

}

Wheel Picker In Action:

Remarks:

I personally think that RecyclerView picker is far better than any other pickers. It comes with all the advantages of RecyclerView. We can use customized item types, add animations and even more.