android 多个viewmodel之间通信

多个viewmodel之间的通信有多种方法，比如通过resposity将sharedviewmodel作为参数传递，进而完成数据通信，也可以通过一个公共的全局变量进行数据传递。本文中提供一个以singleton单例的方式进行。

1.创建单例的resposity类。

Kotlin 复制代码

class testResposity private constructor(){

    //创建单例
    companion object{
        private var INSTANCE:testResposity?=null
        @Synchronized
        fun getInstance():testResposity{
            if(INSTANCE==null)
                INSTANCE = testResposity()
            return INSTANCE!!
        }
    }

    //以下为业务逻辑
    val data = MutableStateFlow<String>("")
    val _counter1 = MutableStateFlow<Int>(0)
    val counter1 = _counter1.asStateFlow()
    fun updateCounter1()
    {
        _counter1.value++
        if(_counter1.value==2)
        {
            data.value = "second"
        }
        else if(_counter1.value == 3)
        {
            data.value = "third"
        }
    }
}

2.创建测试的viewmodel1

Kotlin 复制代码

class TestViewModel1:ViewModel() {
    //获取resposity单例
    private val resposity = testResposity.getInstance()
    val data = resposity.data

    //调用测试逻辑
    public fun updateCounter1(){
        resposity.updateCounter1()
    }
}

3.按照相同的方式，创建测试的viewmodel2

Kotlin 复制代码

class TestViewModel2:ViewModel() {
    private val resposity = testResposity.getInstance()
    val counter = resposity.counter1
    public fun updateCounter(){
        resposity.updateCounter1()
    }
}

4.测试的compose

Kotlin 复制代码

@Composable
fun TestViewModelScreen(modifier: Modifier = Modifier,
                        viewModel:TestViewModel1,
                        viewModel2:TestViewModel2,
                        onClicked:()->Unit,
                        onClicked2:()->Unit
                        ) {

    val counter1 = viewModel.data.collectAsState()
    val counter2 = viewModel2.counter.collectAsState();
    Column {

        Text(text = counter1.value.toString())
        Text(text = counter2.value.toString())

        Button(modifier = Modifier,
            onClick = onClicked
            ) {
            Text(text = "更新")
        }
        Button(
            modifier=Modifier,
            onClick = onClicked2
        ) {
            Text(text="更新2")
        }

    }

}

5.Activity中调用代码

Kotlin 复制代码

var viewModel1=ViewModelProvider(this).get(TestViewModel1::class.java)
            var viewModel2 = ViewModelProvider(this).get(TestViewModel2::class.java)


            TestViewModelTheme {
                Surface(
                    modifier = Modifier.fillMaxSize(),
                )
                {
                    Row (
                        modifier = Modifier.fillMaxSize(),
                        verticalAlignment = Alignment.CenterVertically,
                        horizontalArrangement = Arrangement.Center
                    ){
                        TestViewModelScreen(
                            viewModel = viewModel1,
                            viewModel2=viewModel2,
                            onClicked = {
                                viewModel1.updateCounter1()
                            },
                            onClicked2 = {
                                viewModel2.updateCounter()
                            }
                        )
                    }

                }
            }

6.结果

通过两个不同的viewModel，可以对仓库类中的一个变量进行操作，并同步可显示双方操作结果。