Based on the realization of the android calendar, the effect is good, the code is very simple, you can have a look.

CalendarWidget
..............\.gitignore
..............\.idea
..............\.....\.name
..............\.....\compiler.xml
..............\.....\copyright
..............\.....\.........\profiles_settings.xml
..............\.....\encodings.xml
..............\.....\gradle.xml
..............\.....\misc.xml
..............\.....\modules.xml
..............\.....\runConfigurations.xml
..............\.....\vcs.xml
..............\app
..............\...\.gitignore
..............\...\app.iml
..............\...\build.gradle
..............\...\proguard-rules.pro
..............\...\src
..............\...\...\androidTest
..............\...\...\...........\java
..............\...\...\...........\....\com
..............\...\...\...........\....\...\mrper
..............\...\...\...........\....\...\.....\calendarwidget
..............\...\...\...........\....\...\.....\..............\ApplicationTest.java
..............\...\...\main
..............\...\...\....\AndroidManifest.xml
..............\...\...\....\java
..............\...\...\....\....\com
..............\...\...\....\....\...\mrper
..............\...\...\....\....\...\.....\calendarwidget
..............\...\...\....\....\...\.....\..............\CalendarView.java
..............\...\...\....\....\...\.....\..............\MainActivity.java
..............\...\...\....\res
..............\...\...\....\...\layout
..............\...\...\....\...\......\activity_main.xml
..............\...\...\....\...\......\widget_calendar.xml
..............\...\...\....\...\menu
..............\...\...\....\...\....\menu_main.xml
..............\...\...\....\...\mipmap-hdpi
..............\...\...\....\...\...........\ic_launcher.png
..............\...\...\....\...\mipmap-mdpi
..............\...\...\....\...\...........\ic_launcher.png
..............\...\...\....\...\mipmap-xhdpi
..............\...\...\....\...\............\ic_arrow_left.png
..............\...\...\....\...\............\ic_arrow_right.png
..............\...\...\....\...\............\ic_launcher.png
..............\...\...\....\...\mipmap-xxhdpi
..............\...\...\....\...\.............\ic_launcher.png
..............\...\...\....\...\values
..............\...\...\....\...\values-w820dp
..............\...\...\....\...\.............\dimens.xml
..............\...\...\....\...\......\dimens.xml
..............\...\...\....\...\......\strings.xml
..............\...\...\....\...\......\styles.xml
..............\build.gradle
..............\CalendarWidget.iml
..............\docs
..............\....\img_calendar.png
..............\gradle
..............\gradle.properties
..............\gradlew
..............\gradlew.bat
..............\......\wrapper
..............\......\.......\gradle-wrapper.jar
..............\......\.......\gradle-wrapper.properties
..............\README.md
..............\settings.gradle

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