A Calendar View pager

item_day.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center_vertical">
    <TextView
        android:id="@+id/day_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:text="Sun"
        android:textSize="12sp"
        android:layout_marginBottom="4dp"
        />
    <FrameLayout
        android:id="@+id/day_value_container"
        android:layout_gravity="center"
        android:layout_width="28dp"
        android:layout_height="28dp">
        <TextView
            android:id="@+id/day_value"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:textSize="18sp"
            tools:text="1"
            />
    </FrameLayout>

</LinearLayout>

usage.xml

    <android.support.design.widget.AppBarLayout
        android:id="@+id/appbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="?attr/colorPrimary"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">
        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light"/>

        <com.younility.dispatch.WeekPager
            android:id="@+id/week_pager"
            android:layout_width="match_parent"
            android:layout_height="55dp"/>
    </android.support.design.widget.AppBarLayout>

WeekPager.java

import android.content.Context;
import android.graphics.drawable.Drawable;
import android.graphics.drawable.GradientDrawable;
import android.support.annotation.ColorRes;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.util.AttributeSet;
import android.util.TypedValue;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.TextView;

import com.touchfleet.dispatch.R;

import java.util.ArrayList;
import java.util.Calendar;
import java.util.Date;
import java.util.List;
import java.util.Locale;

import static android.support.v4.view.ViewPager.LayoutParams.MATCH_PARENT;
import static android.support.v4.view.ViewPager.LayoutParams.WRAP_CONTENT;
import static java.util.Calendar.DAY_OF_MONTH;
import static java.util.Calendar.HOUR_OF_DAY;
import static java.util.Calendar.MILLISECOND;
import static java.util.Calendar.MINUTE;
import static java.util.Calendar.MONTH;
import static java.util.Calendar.SECOND;
import static java.util.Calendar.WEEK_OF_YEAR;
import static java.util.Calendar.YEAR;

public class WeekPager extends ViewPager implements View.OnClickListener {
    private final WeekAdapter adapter;
    private final List<WeekDescriptor> weeks;
    private final TypedValue mTypedValue = new TypedValue();

    private Locale locale;
    private Calendar minCal;
    private Calendar maxCal;
    private Calendar today;
    private Calendar selected;
    private Callback callback;

    public WeekPager(Context context, AttributeSet attrs) {
        super(context, attrs);
        this.adapter = new WeekAdapter();
        this.weeks = new ArrayList<>();
        this.locale = Locale.getDefault();
        this.today = Calendar.getInstance(this.locale);
        this.minCal = Calendar.getInstance(this.locale);
        this.maxCal = Calendar.getInstance(this.locale);
        this.selected = Calendar.getInstance(this.locale);

        context.getTheme().resolveAttribute(R.attr.selectableItemBackground, mTypedValue, true);

        if (isInEditMode()) {
            Calendar min = Calendar.getInstance(locale);
            min.add(Calendar.MONTH, -1);

            Calendar max = Calendar.getInstance(locale);
            max.add(Calendar.YEAR, 1);

            init(min.getTime(), max.getTime(), locale);
        }
    }

    public FluentInitializer init(Date minDate, Date maxDate) {
        return init(minDate, maxDate, Locale.getDefault());
    }

    public FluentInitializer init(Date minDate, Date maxDate, Locale locale) {
        if (minDate == null || maxDate == null) {
            throw new IllegalArgumentException(
                "minDate and maxDate must be non-null.  " + dbg(minDate, maxDate));
        }
        if (minDate.after(maxDate)) {
            throw new IllegalArgumentException(
                "minDate must be before maxDate.  " + dbg(minDate, maxDate));
        }
        if (locale == null) {
            throw new IllegalArgumentException("Locale is null.");
        }

        this.weeks.clear();

        this.locale = locale;
        this.today = Calendar.getInstance(this.locale);
        this.minCal = Calendar.getInstance(this.locale);
        this.maxCal = Calendar.getInstance(this.locale);

        this.minCal.setTime(minDate);
        this.maxCal.setTime(maxDate);
        setMidnight(minCal);
        setMidnight(maxCal);

        // maxDate is exclusive: bump back to the previous day so if maxDate is the first of a month,
        // we don't accidentally include that month in the view.
        maxCal.add(MINUTE, -1);

        return new FluentInitializer();
    }

    public void setSelected(Date date) {
        selected.setTime(date);
        validateAndUpdate();

        int page = findPage(selected);
        if (page != -1) {
            setCurrentItem(page, true);
        }
    }

    private int findPage(Calendar date) {
        int week = date.get(WEEK_OF_YEAR);
        int year = date.get(YEAR);
        for (int index = 0; index < weeks.size(); index++) {
            WeekDescriptor descriptor = weeks.get(index);
            if (week == descriptor.week && year == descriptor.year)
                return index;
        }

        return -1;
    }

    @Override
    public void onClick(View v) {
        Date date = (Date) v.getTag();
        selected.setTime(date);
        validateAndUpdate();

        if (callback != null) {
            callback.didSelect(date);
        }
    }

    private List<WeekDayDescriptor> getWeekDayDescriptors(Calendar start) {
        ArrayList<WeekDayDescriptor> descriptors = new ArrayList<>(7);
        Calendar cal = Calendar.getInstance(locale);
        cal.setTime(start.getTime());

        cal.set(Calendar.DAY_OF_WEEK, 1);
        for (int c = 0; c < 7; c++) {
            boolean isToday = sameDate(cal, today);
            int day = cal.get(Calendar.DAY_OF_MONTH);
            String displayName = cal.getDisplayName(Calendar.DAY_OF_WEEK, Calendar.SHORT, locale);

            descriptors.add(new WeekDayDescriptor(
                day, displayName, isToday, cal.getTime()
            ));

            cal.add(Calendar.DAY_OF_WEEK, 1);
        }

        return descriptors;
    }

    private void validateAndUpdate() {
        if (getAdapter() == null) {
            setAdapter(adapter);
        }
        adapter.notifyDataSetChanged();
    }

    private static boolean sameDate(Calendar cal, Calendar selectedDate) {
        return cal.get(MONTH) == selectedDate.get(MONTH)
            && cal.get(YEAR) == selectedDate.get(YEAR)
            && cal.get(DAY_OF_MONTH) == selectedDate.get(DAY_OF_MONTH);
    }

    private static void setMidnight(Calendar cal) {
        cal.set(HOUR_OF_DAY, 0);
        cal.set(MINUTE, 0);
        cal.set(SECOND, 0);
        cal.set(MILLISECOND, 0);
    }

    private static Drawable borderlessDrawable(Context context, @ColorRes int primaryColor) {
        int color = context.getResources().getColor(primaryColor);
        int colors[] = {color, color};

        GradientDrawable shape = new GradientDrawable();
        shape.setShape(GradientDrawable.OVAL);
        shape.setColors(colors);
        shape.setSize(24, 24);

        return shape;
    }

    /** Returns a string summarizing what the client sent us for init() params. */
    private static String dbg(Date minDate, Date maxDate) {
        return "minDate: " + minDate + "\nmaxDate: " + maxDate;
    }

    public interface Callback {
        void didSelect(Date date);
    }

    public class FluentInitializer {
        public FluentInitializer withSelectedDate(Date selectedDates) {
            selected.setTime(selectedDates);
            return this;
        }
        public FluentInitializer withListener(Callback listener) {
            callback = listener;
            return this;
        }

        public void build() {
            Calendar weekCounter = Calendar.getInstance(locale);
            weekCounter.setTime(minCal.getTime());
            final int maxWeek = maxCal.get(WEEK_OF_YEAR);
            final int maxYear = maxCal.get(YEAR);

            while ((weekCounter.get(WEEK_OF_YEAR) <= maxWeek // Up to, including the week.
                || weekCounter.get(YEAR) < maxYear) // Up to the year.
                && weekCounter.get(YEAR) < maxYear + 1) { // But not > next yr.

                int year = weekCounter.get(YEAR);
                int week = weekCounter.get(WEEK_OF_YEAR);
                Date date = weekCounter.getTime();

                final List<WeekDayDescriptor> days = getWeekDayDescriptors(weekCounter);
                weeks.add(new WeekDescriptor(
                    year, week, date, days
                ));

                weekCounter.add(Calendar.WEEK_OF_YEAR, 1);
            }

            final int page = findPage(selected);
            if (page != -1) setCurrentItem(page);
            validateAndUpdate();
        }
    }

    private class WeekAdapter extends PagerAdapter {
        @Override
        public Object instantiateItem(ViewGroup container, int position) {
            Context context = getContext();
            LayoutInflater inflater = LayoutInflater.from(context);
            LinearLayout group = new LinearLayout(context);
            group.setOrientation(LinearLayout.HORIZONTAL);
            group.setLayoutParams(new LinearLayout.LayoutParams(
                MATCH_PARENT, WRAP_CONTENT
            ));
            final WeekDescriptor week = weeks.get(position);
            for (WeekDayDescriptor day : week.days) {
                Calendar date = Calendar.getInstance(locale);
                date.setTime(day.date);

                View view = inflater.inflate(R.layout.item_day, group, false);
                TextView title = (TextView) view.findViewById(R.id.day_title);
                title.setText(day.label);

                TextView value = (TextView) view.findViewById(R.id.day_value);
                String display = String.format("%d", day.day);
                value.setText(display);

                View valueContainer = view.findViewById(R.id.day_value_container);
                boolean isToday = sameDate(today, date);
                boolean isSelected = sameDate(selected, date);

                if (isToday && isSelected) {
                    value.setTextColor(getContext().getResources().getColor(R.color.primary));
                    valueContainer.setBackground(borderlessDrawable(getContext(), R.color.textPrimary));
                } else if (isToday) {
                    value.setTextColor(getContext().getResources().getColor(R.color.accent));
                    valueContainer.setBackgroundResource(android.R.color.transparent);
                } else if (isSelected) {
                    value.setTextColor(getContext().getResources().getColor(R.color.primary));
                    valueContainer.setBackground(borderlessDrawable(getContext(), R.color.accent));
                } else {
                    value.setTextColor(getContext().getResources().getColor(R.color.textPrimary));
                    valueContainer.setBackgroundResource(android.R.color.transparent);
                }

                view.setOnClickListener(WeekPager.this);
                view.setTag(day.date);
                view.setBackgroundResource(mTypedValue.resourceId);

                view.setLayoutParams(new LinearLayout.LayoutParams(
                    0, LayoutParams.WRAP_CONTENT, 1f
                ));
                group.addView(view);
            }

            container.addView(group);
            return group;
        }

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

        @Override
        public int getItemPosition(Object object) {
            return PagerAdapter.POSITION_NONE;
        }

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

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

    private static final class WeekDayDescriptor {
        public final int day;
        public final String label;
        public final boolean isToday;
        public final Date date;

        public WeekDayDescriptor(int day, String label, boolean isToday, Date date) {
            this.day = day;
            this.label = label;
            this.isToday = isToday;
            this.date = date;
        }
    }

    private static final class WeekDescriptor {
        public final int year;
        public final int week;
        public final Date date;
        public final List<WeekDayDescriptor> days;

        public WeekDescriptor(int year, int week, Date date, List<WeekDayDescriptor> days) {
            this.year = year;
            this.week = week;
            this.date = date;
            this.days = days;
        }

        @Override
        public String toString() {
            return "WeekDescriptor {" +
                "year=" + year +
                ", week=" + week +
                ", date=" + date +
                '}';
        }
    }
}

This is a reproduction of the iOS8 calendar date picker widget. It uses a similar API to the Square Android TimeSquare API.

        Locale locale = Locale.getDefault();
        Calendar min = Calendar.getInstance(locale);
        min.add(Calendar.MONTH, -3);

        Calendar max = Calendar.getInstance(locale);
        max.add(Calendar.YEAR, 1);
        updateTitle(activeDate);
        weekPager
            .init(min.getTime(), max.getTime(), locale)
            .withSelectedDate(activeDate)
            .withListener(this)
            .build();

I had to hard-code the height of the Pager because when the ViewPager's layout_height is set to wrap_content, it ends up taking up the whole screen.

I find setting the title of the activity useful. I use a method similar to this

    private void updateTitle(Date date) {
        Locale locale = Locale.getDefault();
        Calendar cal = Calendar.getInstance(locale);
        int year = cal.get(Calendar.YEAR);

        cal.setTime(date);
        int titleYear = cal.get(Calendar.YEAR);

        if (titleYear != year) {
            final String shortMonth = cal.getDisplayName(Calendar.MONTH, Calendar.SHORT, locale);
            toolbar.setTitle(shortMonth + " " + titleYear);
        } else {
            final String longMonth = cal.getDisplayName(Calendar.MONTH, Calendar.LONG, locale);
            toolbar.setTitle(longMonth);
        }
    }

TODO: I still need to add support for selecting the first day of the month when you swipe pages.