构建点击计数器
将状态连接到按钮，实现实时更新。
构建点击计数器 是 CoddyKit 上的免费 Jetpack Compose Academy 课时。 这是第 3 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 Jetpack Compose Academy 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Jetpack Compose Academy 课程共包含 4 节课。
本课时的部分内容尚未翻译，以英文显示。
Our Goal
Let's build a tiny tap counter: a number on screen and a button that increases it with every tap. 🙂
Start With the State
First declare the state that will change. The counter starts at zero and lives inside the Composable for now.
var count by remember { mutableStateOf(0) }Show the Count
Read the state in a Text so it always displays the current value. Reading it here subscribes the Text to changes.
Text("Count: " + count)Add the Button
A Button needs an onClick action. Inside it we will change the state, which is what makes the UI react.
Button(onClick = { }) {
Text("Tap me")
}Increment on Tap
In onClick, bump the counter. Changing the state tells Compose to recompose anything that reads count.
Button(onClick = { count++ }) {
Text("Tap me")
}Stack Them in a Column
Place the text above the button using a Column, which lays out its children vertically, top to bottom.
Column {
Text("Count: " + count)
Button(onClick = { count++ }) { Text("Tap me") }
}How the Loop Works
Tap fires onClick, count changes, Compose recomposes the Text, and you instantly see the new number. That is the full cycle.
Add a Reset Button
Want a fresh start? Add a second button whose onClick sets count back to zero. Reset is just another state change.
Button(onClick = { count = 0 }) {
Text("Reset")
}React to the Value
Because the UI is a function of state, you can style it from count, like showing a message once it passes ten taps.
if (count > 10) Text("Wow, keep going!")Wrap It in a Function
Put everything in a reusable Composable named TapCounter. Now you can drop your counter anywhere in the app.
@Composable
fun TapCounter() {
var count by remember { mutableStateOf(0) }
}You Built Interactivity
That simple loop of state to UI to event to state is the heart of every interactive Compose screen you will ever write.
Quick Check
What makes the displayed number update after a tap?
Recap
You wired state to a Text and a Button to build a live tap counter, your first truly interactive Compose screen. Great work! 🎉
常见问题解答
「构建点击计数器」课时是免费的吗？
是的 — 「构建点击计数器」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Jetpack Compose Academy 课程的其余内容，请升级到 CoddyKit PRO。 Jetpack Compose Academy 课程共包含 4 节课。
「构建点击计数器」这节课中我会学到什么？
将状态连接到按钮，实现实时更新。 你通过在浏览器中直接运行的动手代码来练习 Jetpack Compose Academy，全天候 AI 导师会在你学习这节课的过程中回答你的问题。
学习 Jetpack Compose Academy 需要有经验吗？
无需任何先前经验。CoddyKit 上的 Jetpack Compose Academy 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 3 节课，共 4 节。
「构建点击计数器」课时需要多长时间？
大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。
我能在这节 Jetpack Compose Academy 课中编写并运行代码吗？
能。每节 Jetpack Compose Academy 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。