class MyViewModel(application: Application) : AndroidViewModel(application) {
    var number = 0 //
}

class TestActivity : AppCompatActivity() {
    private var textView: TextView? = null
    private var viewModel: MyViewModel? = null
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        textView = findViewById(R.id.textView)
        //實例化viewModel
        viewModel =ViewModelProvider(this, 
            AndroidViewModelFactory(application))[MyViewModel::class.java]
        //顯示數(shù)據(jù)
        textView!!.text = String.valueOf(viewModel!!.number)
    }
       //點擊事件
    fun plusNumber(view: View) {
        textView!!.text = String.valueOf(++viewModel!!.number)
    }
}

class MyViewModel : ViewModel() {
	//定義LiveData集合
    private var linkNumber: MutableLiveData<Int>? = null
	//得到LiveData集合
    fun getLinkNumber(): MutableLiveData<Int>? {
        if (linkNumber == null) {
        	//初始化
            linkNumber = MutableLiveData()
            linkNumber!!.value = 0
        }
        return linkNumber
    }
	//給外部提供修改集合內(nèi)部屬性的方法
    fun addLinkedNumber(n: Int) {
        linkNumber!!.value = linkNumber!!.value!! + n
    }
}

class MainActivity : AppCompatActivity() {
    private var viewModel: MyViewModel? = null
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val textView: TextView = findViewById(R.id.textView)
        viewModel =ViewModelProvider(this, 
            AndroidViewModelFactory(application))[MyViewModel::class.java]
        //觀察
        viewModel!!.getLinkNumber()!!.observe(this, Observer {
            textView.text = String.valueOf(it)
        })
    }
    fun reduce(view: View) {
        viewModel!!.addLinkedNumber(-1)
    }
    fun add(view: View) {
        viewModel!!.addLinkedNumber(1)
    }
}