Jetpack Compose是什么?

Jetpack Compose 是安卓用于构建UI的一种新方式,采用代码而非xml文件方式，写法与Flutter非常相似。
官方主页：https://developer.android.google.cn/jetpack/compose
官方Demo：https://github.com/android/compose-samples/tree/master/JetNews
官方入门指导: https://developer.android.google.cn/jetpack/compose/tutorial

约束条件

1. Android Studio: 4.0及以上
2. 支持安卓版本:Android API 21(即5.0)及以上
3. 必须使用kotlin语言

优点

1. 代码更少

   少了xml,少了activity和xml之间的关联.

2. 双向绑定

   数据变化了,UI就自动变化.

缺点

1. 含有参数的Composable函数不能直接预览.
2. Composable函数必须添加@Preview注解才能预览.
3. 代码修改后,需要重新编译才能预览.
4. 目前还不完善,相比于Flutter,还处于幼儿园水平.
5. 相比于xml画页面布局,效率会有降低.

常见控件使用样例

1. 文本显示

Text(text = "众鸟高飞尽，孤云独去闲。相看两不厌，只有敬亭山。") 

2. 文本输入框

val state = +state { "Text Field to input" } TextField( value = state.value, onValueChange = { state.value = it } ) 

3. 按钮

Button(text = "咬我啊", onClick = { Log.v("test", "被咬了") }) 

4.弹出框

MaterialTheme { Column { val openDialog = +state { false } Button("Click me", onClick = { openDialog.value = true }) if (openDialog.value) { AlertDialog( onCloseRequest = { openDialog.value = false }, title = { Text(text = "Alert Dialog Title") }, text = { Text("Alert Dialog content") }, confirmButton = { Button( "Confirm", onClick = { openDialog.value = false }) }, dismissButton = { Button( "Cancel", onClick = { openDialog.value = false }) }, buttonLayout = AlertDialogButtonLayout.Stacked ) } } } 

5. 开关

MaterialTheme { val checkedState = +state { true } Switch( checked = checkedState.value, onCheckedChange = { checkedState.value = it } ) } 

6. 单选框

MaterialTheme { RadioButton(selected = true, onSelect = { } ) } 

7. 复选框

MaterialTheme { val checkedState = +state { true } Checkbox( checked = checkedState.value, onCheckedChange = { checkedState.value = it } ) } 

8. 单选框组

MaterialTheme { val radioOptions = listOf("A", "B", "C") val (selectedOption, onOptionSelected) = +state { radioOptions[0] } RadioGroup( options = radioOptions, selectedOption = selectedOption, onSelectedChange = onOptionSelected ) } 

9.图片

Container(modifier = Height(300.dp) wraps Expanded) { Clip(shape = RoundedCornerShape(4.dp)) { DrawImage(+imageResource(R.drawable.img_0)) }}

源代码

https://github.com/cxyzy1/Jetpack-Compose-Demos
推荐阅读：37岁老码农现身说法：那些年，我走过的弯路

作者：程序园中猿
链接：https://www.jianshu.com/p/4289c2271c95