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val 就是 value

var number:Int = 0        var l:String = "888"

package com.lyr.myapplicationimport androidx.appcompat.app.AppCompatActivityimport android.os.Bundleimport kotlinx.android.synthetic.main.activity_example.*class ExampleActivity : AppCompatActivity() {
       override fun onCreate(savedInstanceState: Bundle?) {
           super.onCreate(savedInstanceState)        setContentView(R.layout.activity_example)        var number = 0        this.textView.text = ""        btn_add.setOnClickListener{
               textView.text = (number++).toString()        }        btn_decr.setOnClickListener{
               textView.text = (number--).toString()        }    }}

package com.lyr.myapplicationimport androidx.appcompat.app.AppCompatActivityimport android.os.Bundleimport androidx.lifecycle.Observerimport androidx.lifecycle.ViewModelimport androidx.lifecycle.ViewModelProviderimport com.lyr.myapplication.vm.MyViewModelimport kotlinx.android.synthetic.main.activity_example.*class ExampleActivity : AppCompatActivity() {
       override fun onCreate(savedInstanceState: Bundle?) {
           super.onCreate(savedInstanceState)        setContentView(R.layout.activity_example)        val vm :MyViewModel = ViewModelProvider(this).get(MyViewModel::class.java)//        this.textView.text = vm.number.value.toString()        vm.number.observe(this, Observer{
               textView.text = it.toString()        })        btn_add.setOnClickListener{
               vm.modifyNumber(1)        }        btn_decr.setOnClickListener{
   //            textView.text = (number--).toString()            vm.modifyNumber(-1)        }    }}

package com.lyr.myapplication.vmimport androidx.lifecycle.MutableLiveDataimport androidx.lifecycle.ViewModel/** * view model * @Author  lyr * @create 2020/10/11 20:11 */class MyViewModel : ViewModel() {
       val number: MutableLiveData
   
     by lazy {
           MutableLiveData
    
     ().also {
                   it.value = 0            }    }    fun modifyNumber(n:Int) {
           number.value = number.value?.plus(n)//        //强制执行//        number.value = number.value!!.plus(n)    }}
    
   

getter 方式的写法

class MyViewModel : ViewModel() {
       private val _number: MutableLiveData
   
     by lazy {
           MutableLiveData
    
     ().also {
               it.value = 0        }    }    val number: LiveData
     
       get() = _number    fun modifyNumber(n: Int) {
           _number.value = _number.value?.plus(n)//        //强制执行//        number.value = number.value!!.plus(n)    }}
     
    
   

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