一、用KMM写Flutter插件
Google官方有一个写Flutter例子How to write a Flutter plugin，这里把Google plugin_codelab 例子改成用KMM写Flutter插件。
二、如何运行
Github项目地址：kmm-flutter-plugin
Android: run shared/plugin_codelab/example/android
iOS:
1、build shared.framework
use ./gradlew releaseIOSFramework
or use new version Android Studio sync
2、run shared/plugin_codelab/example/ios
Tips: before run，shared/build/cocoapods/framework/shared.framework should be generated. The shared.h header file shared/build/cocoapods/framework/shared.framework/Headers/shared.h is generated.
三、设计思路
Android/iOS插件PluginCodelabPlugin只需要实现KMM Module的接口，不写任何逻辑，把逻辑通过接口放在KMM Module中。
1、定义接口中间层用于转发数据
如参考Flutter插件的MethodCall、MethodChannel，定义CommonMethodCall数据类、CommonMethodChannel.Result接口。
data class CommonMethodCall(
val method: String,
val arguments: Any?,
)
class CommonMethodChannel {
interface Result {
fun success(result: Any?)
fun error(errorCode: String?, errorMessage: String?, errorDetails: Any?)
fun notImplemented()
}
}
2、在KMM中的commonMain实现CommonCodelabPlugin插件的公共逻辑
CommonCodelabPlugin需要初始化并启动synth?.start()，处理getPlatformVersion、onKeyDown、onKeyUp逻辑。
class CommonCodelabPlugin {
private val synth = Synth()
init {
synth?.start()
}
fun onMethodCall(call: CommonMethodCall, result: CommonMethodChannel.Result) {
when (call.method) {
"getPlatformVersion" -> {
result.success(Platform().platform)
}
"onKeyDown" -> {
try {
val arguments = call.arguments as List<*>
val numKeysDown = synth?.keyDown((arguments[0] as Int))
result.success(numKeysDown)
} catch (ex: Exception) {
result.error("1", ex.message, ex.cause)
}
}
"onKeyUp" -> {
try {
val arguments = call.arguments as List<*>
val numKeysDown = synth?.keyUp((arguments[0] as Int))
result.success(numKeysDown)
} catch (ex: Exception) {
result.error("1", ex.message, ex.cause)
}
}
else -> {
result.notImplemented()
}
}
}
}
还有包括插件名称也属于公共逻辑
// 插件Channel名称
const val PLUGIN_CODE_LAB_CHANNEL = "plugin_codelab"
3、实现平台差异特性
这里只列出expect接口，具体实现平台差异特性类请查看源码
expect class Synth() {
fun start()
fun keyDown(key: Int): Int
fun keyUp(key: Int): Int
}
expect class Platform() {
val platform: String
}
4、Android Flutter实现插件KMM接口
Android Flutter实现插件KMM接口，注意这里只实现接口用于中转Flutter与Android/iOS 数据，不能有任何业务逻辑
class PluginCodelabPlugin : FlutterPlugin, MethodCallHandler {
private var channel: MethodChannel? = null
private var commonCodelabPlugin: CommonCodelabPlugin? = null
override fun onAttachedToEngine(flutterPluginBinding: FlutterPlugin.FlutterPluginBinding) {
setup(this, flutterPluginBinding.binaryMessenger)
}
override fun onMethodCall(call: MethodCall, result: MethodChannel.Result) {
commonCodelabPlugin?.onMethodCall(
call = CommonMethodCall(call.method, call.arguments),
result = object : CommonMethodChannel.Result {
override fun success(successResult: Any?) {
result.success(successResult)
}
override fun error(errorCode: String?, errorMessage: String?, errorDetails: Any?) {
result.error(errorCode, errorMessage, errorDetails)
}
override fun notImplemented() {
result.notImplemented()
}
})
}
override fun onDetachedFromEngine(binding: FlutterPlugin.FlutterPluginBinding) {
channel?.setMethodCallHandler(null)
}
companion object {
private fun setup(plugin: PluginCodelabPlugin, binaryMessenger: BinaryMessenger) {
plugin.channel = MethodChannel(binaryMessenger, PLUGIN_CODE_LAB_CHANNEL)
plugin.channel?.setMethodCallHandler(plugin)
plugin.commonCodelabPlugin = CommonCodelabPlugin()
}
}
}
5、iOS Flutter实现插件KMM接口
Android Flutter实现插件KMM接口，注意这里只实现接口用于中转Flutter与Android/iOS 数据，不能有任何业务逻辑
#import "PluginCodelabPlugin.h"
@implementation PluginCodelabPlugin{
int _numKeysDown;
FlutterResult _flutterResult;
SharedCommonCodelabPlugin* _codelabPlugin;
}
- (instancetype)init {
self = [super init];
if (self) {
// create music
_codelabPlugin = [[SharedCommonCodelabPlugin alloc] init];
}
return self;
}
- (void)dealloc {
// destroy music
}
+ (void)registerWithRegistrar:(NSObject*)registrar {
FlutterMethodChannel* channel = [FlutterMethodChannel
methodChannelWithName: SharedPluginCodeLabKt.PLUGIN_CODE_LAB_CHANNEL
binaryMessenger:[registrar messenger]];
PluginCodelabPlugin* instance = [[PluginCodelabPlugin alloc] init];
[registrar addMethodCallDelegate:instance channel:channel];
}
- (void)handleMethodCall:(FlutterMethodCall *)call
result:(FlutterResult)result {
SharedCommonMethodCall *methodCall = [[SharedCommonMethodCall alloc] initWithMethod:call.method arguments:call.arguments];
_flutterResult = result;
[_codelabPlugin onMethodCallCall:methodCall result:self ];
}
- (void)errorErrorCode:(NSString * _Nullable)errorCode errorMessage:(NSString * _Nullable)errorMessage errorDetails:(id _Nullable)errorDetails {
NSError *error = [NSError errorWithDomain:NSCocoaErrorDomain code:errorCode.intValue userInfo:@{@"errorMessage":errorMessage, @"errorDetails":errorDetails}];
if (_flutterResult) {
_flutterResult(error);
}
}
- (void)notImplemented {
if (_flutterResult) {
_flutterResult(FlutterMethodNotImplemented);
}
}
- (void)successResult:(id _Nullable)result {
if (_flutterResult) {
_flutterResult(result);
}
}
@end
到这里，已经完成了使用KMM开发一个Flutter插件。使用KMM开发插件的好处是公共逻辑都使用kotlin写，一般公共逻辑比较简单适合使用kotlin写，便于维护。而且，实现了KMM写插件，Flutter写UI。
四、参考链接
本文地址：https://www.cnblogs.com/liqw/p/15477079.html
Github项目地址：kmm-flutter-plugin