使用视图模型向MutableList添加项目

import androidx.lifecycle.LiveData
import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.ViewModel

class MyViewModel : ViewModel() {
    // 使用MutableLiveData来包装MutableList
    private val _items = MutableLiveData<MutableList<String>>()
    val items: LiveData<MutableList<String>> get() = _items

    init {
        // 初始化列表
        _items.value = mutableListOf()
    }

    fun addItem(item: String) {
        // 获取当前的列表并添加新项目
        val currentList = _items.value?.toMutableList() ?: mutableListOf()
        currentList.add(item)
        _items.value = currentList
    }
}

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.lifecycle.Observer
import androidx.lifecycle.ViewModelProvider
import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity() {
    private lateinit var viewModel: MyViewModel

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        viewModel = ViewModelProvider(this).get(MyViewModel::class.java)

        // 观察items的变化并更新UI
        viewModel.items.observe(this, Observer { items ->
            // 更新UI，例如更新ListView或RecyclerView的适配器
            item_list.adapter = ArrayAdapter(this, android.R.layout.simple_list_item_1, items)
        })

        // 添加按钮点击事件
        add_button.setOnClickListener {
            viewModel.addItem("New Item")
        }
    }
}