MaterialDatePicker not working on Android

With the Material Components for Android you can use the new MaterialDatePicker.

To work fine, in your app you have to use a Material Components Theme.
In this way you inherit the style and theme for the pickers.

To select a single date just use:

MaterialDatePicker.Builder<Long> builder = MaterialDatePicker.Builder.datePicker();
builder.setTitleText(R.string.your_text);
MaterialDatePicker<Long> picker = builder.build();
picker.show(getSupportFragmentManager(), picker.toString());

To select a range date you can use a DateRange Picker using:

MaterialDatePicker.Builder<Pair<Long, Long>> builder =
                    MaterialDatePicker.Builder.dateRangePicker();
CalendarConstraints.Builder constraintsBuilder = new CalendarConstraints.Builder();
builder.setCalendarConstraints(constraintsBuilder.build());
MaterialDatePicker<?> picker = builder.build();
picker.show(getSupportFragmentManager(), picker.toString());

Check the colors used in your theme.

These attributes define your style. You don't need to add them, they are provided by default with the Material Components theme.

<!-- Picker styles and themes. -->
<item name="materialCalendarStyle">@style/Widget.MaterialComponents.MaterialCalendar</item>
<item name="materialCalendarFullscreenTheme">@style/ThemeOverlay.MaterialComponents.MaterialCalendar.Fullscreen</item>
<item name="materialCalendarTheme">@style/ThemeOverlay.MaterialComponents.MaterialCalendar</item>

Based on these style, the colors used by the picker are:

HeaderLaoyout     -> background:colorPrimary, textColor:colorOnPrimary
HeaderSelection   -> background:colorPrimary, textColor:colorOnPrimary
ConfirmButtons    -> background:colorPrimary, textColor:colorOnPrimary
Buttons           -> background:colorPrimary, textColor:colorOnSurface
HeaderToggleButton->                          textColor:colorOnPrimary
Day               ->                          text:colorOnSurface  stroke:colorOnSurface
SelectedDay       -> background:colorPrimary, textColor:colorOnPrimary
RangeFillColor    -> background:colorPrimary

The problem was in the colorPrimary.

The default color of my project to colorPrimary was "white" and the Material Date Picker style uses that colorPrimary to color the background and the text of the buttons. Since the color of the header text was also white, it appear that there was nothing there when there was everything.

I solved it by importing the styles file to my project and making some adjustments to the styles in my project.

Thank you all for your answers, all of them helped in finding the problem!

I had the same issue with my primary color being white.

The simple solution is to override the primaryColor in the Calendar style:

Base Theme:

<style name="Base.Theme.YV.Bible" parent="Theme.MaterialComponents.DayNight.NoActionBar">
  <item name="materialCalendarStyle">@style/Theme.YV.Bible.DatePicker</item>
  <item name="android:datePickerDialogTheme">@style/Theme.YV.Bible.DatePicker</item>
</style>

Calendar / Datepicker Theme

<style name="Theme.YV.Bible.DatePicker" parent="ThemeOverlay.MaterialComponents.MaterialCalendar">
  <item name="colorPrimary">?colorPrimaryDark</item> // this is the key, we need to use a dark color instead of our theme's primary color
</style>

Usage

val picker = MaterialDatePicker.Builder
    .datePicker()
    .setCalendarConstraints(CalendarConstraints.Builder().setStart(now().time).build())
    .setSelection(c.timeInMillis)
    .setTheme(com.bible.base.R.style.Theme_YV_Bible_DatePicker)
    .build()
picker.show(fragmentManager, null)