How to Make a Calendar App
How to Vibe Code a Native Calendar & Planner App
Stay in your creative flow. Direct AI models with high-level intent, build an interactive month/week strip and time-blocking agenda in Jetpack Compose, and run your personal planner APK in under 30 minutes.
Core Stack
Kotlin Compose
Date Engine
java.time LocalDate
AI Partner
Claude / Gemini
Target Time
20–30 Mins
The Vibe Coding Mobile Philosophy
Building a calendar app the old-fashioned way meant wrestling legacy java.util.Calendar zero-indexed months, nested RecyclerViews for day cells, and complex alarm broadcasts.
Vibe coding lets you focus on the daily planning experience: you describe the date strip, color-coded time blocks, and task checkboxes while your AI assistant generates clean java.time.LocalDate Compose code in a single file.
Old-School Mobile Stress
- Fighting off-by-one month bugs in legacy
java.util.CalendarandSimpleDateFormat. - Writing three separate RecyclerView adapters for Month, Week, and Day agenda views.
- Manually wiring complex SQLite joins to filter events by selected date.
- Spending hours building a custom time-slot picker dialog in XML.
The Vibe Coder Way
- Modern
java.time.LocalDatemath rendered in a reactive Jetpack Compose date strip and month grid. - Describe the vibe: "Sleek daily time-blocking planner with event indicator dots and quick-add bottom sheet."
- Ask AI to group events by
LocalDatein memory or Room with zero boilerplate. - Deploy directly to your phone over Wi-Fi and plan your real week immediately.
The 4-Step Blueprint
From an empty Compose project to a daily schedule and time-blocking planner on your phone.
Spawning the Empty Compose Canvas
Open Android Studio and select New Project > Empty Activity (with Compose logo). Name it VibeCalendar with minimum SDK 26+ (so java.time works out of the box).
minSdk = 26 gives LLMs native access to LocalDate and LocalTime without needing core library desugaring in Gradle.
The "One-Shot Architect" Prompt
Prompt the AI for a unified screen: a selectable 7-day or month calendar header, event indicator dots on busy dates, and a chronological daily timeline below.
LocalDate state, and event models inside one MainActivity.kt so I can run it immediately."
Time-Blocking & Micro-Interactions
Add color-coded category tags (Deep Work, Meeting, Personal, Fitness), a quick-add modal bottom sheet, and smooth animated transitions when switching days.
Run on Your Real Phone
Pair your Android phone via Wireless Debugging, hit Run (Shift+F10), and test adding and checking off events for today and tomorrow.
Vibe Prompt Configurator
Pick your planner aesthetic, storage layer, and scheduling features to generate a ready-to-paste LLM prompt.
Essential Elements of a Calendar App
To deliver a comprehensive, stress-free scheduling experience, make sure your calendar app includes these core pillars:
-
Effortless Schedule Management
Let users add, edit, and delete events in just a few taps, and switch smoothly between Day, Week, and Month views to plan ahead.
-
Notifications & Recurring Reminders
Trigger timely alerts before appointments with location or contact notes, plus recurring schedules so weekly routines are never missed.
-
Integrated Task Management
Combine calendar appointments with checkable to-do tasks and deadlines in one unified daily view so nothing falls through the cracks.
-
Visual Time Blocking
Allow users to dedicate color-coded blocks of time for deep work, calls, or workouts to maximize daily focus and productivity.
-
Cross-Device Sync & Export
Keep schedules consistent across devices or allow quick ICS/JSON import and export so events are accessible anywhere.
-
Privacy, Security & Clean UI
Protect personal schedule data locally (with optional biometric/PIN lock) inside an uncluttered, high-contrast calendar interface.
The "Golden" Single-File Compose Template
Replace the contents of your MainActivity.kt with this to run a working time-blocking calendar app right now.
package com.example.vibecalendar
import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.foundation.background
import androidx.compose.foundation.clickable
import androidx.compose.foundation.layout.*
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.foundation.lazy.LazyRow
import androidx.compose.foundation.lazy.items
import androidx.compose.foundation.shape.CircleShape
import androidx.compose.foundation.shape.RoundedCornerShape
import androidx.compose.material.icons.Icons
import androidx.compose.material.icons.filled.Add
import androidx.compose.material.icons.filled.Delete
import androidx.compose.material3.*
import androidx.compose.runtime.*
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.clip
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.text.font.FontWeight
import androidx.compose.ui.text.style.TextDecoration
import androidx.compose.ui.unit.dp
import androidx.compose.ui.unit.sp
import java.time.LocalDate
import java.time.format.TextStyle
import java.util.Locale
import java.util.UUID
data class CalendarEvent(
val id: String = UUID.randomUUID().toString(),
val date: LocalDate,
val timeBlock: String,
val title: String,
val category: String = "Work",
val isDone: Boolean = false
)
class MainActivity : ComponentActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContent {
MaterialTheme(
colorScheme = darkColorScheme(
background = Color(0xFF0B111E),
surface = Color(0xFF151F32),
primary = Color(0xFF6366F1)
)
) {
Surface(modifier = Modifier.fillMaxSize(), color = MaterialTheme.colorScheme.background) {
VibeCalendarScreen()
}
}
}
}
}
@Composable
fun VibeCalendarScreen() {
val today = remember { LocalDate.now() }
var selectedDate by remember { mutableStateOf(today) }
var events by remember {
mutableStateOf(
listOf(
CalendarEvent(date = today, timeBlock = "09:00 AM", title = "Deep Work: Architecture Review", category = "Focus"),
CalendarEvent(date = today, timeBlock = "01:30 PM", title = "Product Design Sync", category = "Work"),
CalendarEvent(date = today.plusDays(1), timeBlock = "10:00 AM", title = "Ship Calendar APK to Phone", category = "Launch")
)
)
}
var newTitle by remember { mutableStateOf("") }
var newTime by remember { mutableStateOf("11:00 AM") }
val weekDays = remember(today) { (-2..11).map { today.plusDays(it.toLong()) } }
val dayEvents = events.filter { it.date == selectedDate }
Scaffold(
topBar = {
Row(
modifier = Modifier
.fillMaxWidth()
.statusBarsPadding()
.padding(horizontal = 20.dp, vertical = 16.dp),
horizontalArrangement = Arrangement.SpaceBetween,
verticalAlignment = Alignment.CenterVertically
) {
Column {
Text(
text = "${selectedDate.month.getDisplayName(TextStyle.FULL, Locale.US)} ${selectedDate.year}",
fontSize = 24.sp,
fontWeight = FontWeight.ExtraBold,
color = Color.White
)
Text(
text = "${dayEvents.size} scheduled items • time-block flow",
fontSize = 13.sp,
color = Color(0xFF94A3B8)
)
}
TextButton(onClick = { selectedDate = today }) {
Text("Today", color = Color(0xFF818CF8), fontWeight = FontWeight.Bold)
}
}
},
containerColor = Color.Transparent
) { innerPadding ->
Column(
modifier = Modifier
.padding(innerPadding)
.fillMaxSize()
.padding(horizontal = 20.dp),
verticalArrangement = Arrangement.spacedBy(16.dp)
) {
// Horizontal Date Strip
LazyRow(horizontalArrangement = Arrangement.spacedBy(10.dp)) {
items(weekDays) { date ->
val isSelected = date == selectedDate
val hasEvents = events.any { it.date == date }
Column(
modifier = Modifier
.width(58.dp)
.clip(RoundedCornerShape(16.dp))
.background(if (isSelected) Color(0xFF6366F1) else Color(0xFF151F32))
.clickable { selectedDate = date }
.padding(vertical = 12.dp),
horizontalAlignment = Alignment.CenterHorizontally
) {
Text(
text = date.dayOfWeek.getDisplayName(TextStyle.SHORT, Locale.US),
fontSize = 11.sp,
color = if (isSelected) Color.White else Color(0xFF94A3B8)
)
Spacer(modifier = Modifier.height(4.dp))
Text(
text = date.dayOfMonth.toString(),
fontSize = 18.sp,
fontWeight = FontWeight.ExtraBold,
color = Color.White
)
Spacer(modifier = Modifier.height(6.dp))
Box(
modifier = Modifier
.size(6.dp)
.clip(CircleShape)
.background(
when {
hasEvents && isSelected -> Color.White
hasEvents -> Color(0xFF34D399)
else -> Color.Transparent
}
)
)
}
}
}
// Quick Add Time-Block Row
Row(
modifier = Modifier.fillMaxWidth(),
horizontalArrangement = Arrangement.spacedBy(8.dp),
verticalAlignment = Alignment.CenterVertically
) {
OutlinedTextField(
value = newTime,
onValueChange = { newTime = it },
modifier = Modifier.width(108.dp),
singleLine = true,
label = { Text("Time", fontSize = 11.sp) }
)
OutlinedTextField(
value = newTitle,
onValueChange = { newTitle = it },
modifier = Modifier.weight(1f),
singleLine = true,
label = { Text("Add time block or task...", fontSize = 11.sp) }
)
FloatingActionButton(
onClick = {
if (newTitle.isNotBlank()) {
events = events + CalendarEvent(
date = selectedDate,
timeBlock = newTime.ifBlank { "All Day" },
title = newTitle.trim()
)
newTitle = ""
}
},
containerColor = Color(0xFF6366F1),
contentColor = Color.White,
modifier = Modifier.size(50.dp)
) {
Icon(Icons.Default.Add, contentDescription = "Add Event")
}
}
// Daily Agenda List
LazyColumn(
modifier = Modifier.weight(1f),
verticalArrangement = Arrangement.spacedBy(10.dp)
) {
items(dayEvents, key = { it.id }) { ev ->
Row(
modifier = Modifier
.fillMaxWidth()
.clip(RoundedCornerShape(16.dp))
.background(Color(0xFF151F32))
.clickable {
events = events.map { if (it.id == ev.id) it.copy(isDone = !it.isDone) else it }
}
.padding(16.dp),
verticalAlignment = Alignment.CenterVertically
) {
Column(modifier = Modifier.width(76.dp)) {
Text(ev.timeBlock, color = Color(0xFF818CF8), fontWeight = FontWeight.Bold, fontSize = 12.sp)
Text(ev.category, color = Color(0xFF64748B), fontSize = 11.sp)
}
Column(modifier = Modifier.weight(1f)) {
Text(
text = ev.title,
color = if (ev.isDone) Color(0xFF64748B) else Color.White,
textDecoration = if (ev.isDone) TextDecoration.LineThrough else TextDecoration.None,
fontWeight = FontWeight.SemiBold,
fontSize = 15.sp
)
}
IconButton(onClick = { events = events.filter { it.id != ev.id } }) {
Icon(Icons.Default.Delete, contentDescription = "Delete", tint = Color(0xFFF43F5E))
}
}
}
}
}
}
}How to Debug Without Losing Your Vibe
Keep date math and notifications smooth with these three vibe debugging rules:
The Error Dump Rule
If LocalDate shows an API level warning, paste the warning into your AI chat:
"Set minSdk = 26 in build.gradle.kts or show me coreLibraryDesugaring so java.time compiles cleanly."
Immutable LocalDate Keys
Avoid mutable `Date` objects that fail to trigger Compose recomposition: "Use immutable java.time.LocalDate and YearMonth for all calendar state so Compose updates immediately."
Instant Wireless Run
Connect your Android phone over Wi-Fi once and use Apply Changes to test horizontal week-strip scrolling at 60fps.
The Vibe Prompt Vault
Copy-paste prompts to expand your planner with full month grids, notifications, and Pomodoro time-blocking.
🗓️ Prompt: Add an Expandable 7-Column Full Month Grid View
"Update my Jetpack Compose Calendar app in MainActivity.kt so tapping the Month/Year title smoothly expands and collapses between the 7-day week strip and a full 7-column YearMonth calendar grid with previous/next month arrows and colored event indicator dots."
🔔 Prompt: Schedule Exact Event Reminders with AlarmManager
"Add local push notifications to my Compose Calendar app. When a user creates an event with a reminder toggle, schedule a notification 15 minutes before the event time using WorkManager or AlarmManager, including Android 13+ POST_NOTIFICATIONS permission handling."
⏱️ Prompt: Add a Focus Timer Inside Each Time Block
"Allow tapping any scheduled time block in my Compose Calendar app to launch a 25-minute countdown focus timer sheet tied to that event, automatically marking the time block as completed when the timer finishes."