LiveData和ViewModel的關(guān)系

• 在ViewModel中的數(shù)據(jù)發(fā)生變化是通知頁(yè)面

  
  
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  當(dāng)ViewModel數(shù)據(jù)發(fā)生變化通過(guò)LiveData通知View數(shù)據(jù)變化進(jìn)行更新

LiveData應(yīng)用：

• 非UI線程使用postValue
• UI線程使用setValue

class MyViewModel :ViewModel() {
    private lateinit var liveData:MutableLiveData<Int>

   fun getCurrentSecond():MutableLiveData<Int>{
        if(!this::liveData.isInitialized){
            liveData = MutableLiveData()
            liveData.value = 0
        }
        return liveData
    }
}

class Test2Activity : AppCompatActivity() {

    private var viewModel: MyViewModel? = null
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_test2)

        viewModel =
            ViewModelProvider(this, ViewModelProvider.AndroidViewModelFactory(application)).get(
                MyViewModel::class.java
            )
        findViewById<TextView>(R.id.textView).text = viewModel?.getCurrentSecond()?.value.toString()
        viewModel?.getCurrentSecond()?.observe(this) {
            findViewById<TextView>(R.id.textView).text = it.toString()
        }
        startTime()
    }

    private fun startTime() {
        Timer().schedule(
            object : TimerTask() {
                override fun run() {
                    viewModel?.getCurrentSecond()
                        ?.postValue((viewModel?.getCurrentSecond()?.value?.plus(1)))
                }

            },
            1000,
            1000
        )
    }
}

LiveData的優(yōu)勢(shì)：

• 確保頁(yè)面符合數(shù)據(jù)狀態(tài)
• 不會(huì)發(fā)生內(nèi)存泄漏
• 不會(huì)因Activity停止而導(dǎo)致崩潰
• 不在需要手動(dòng)處理生命周期
• 數(shù)據(jù)始終保持最新?tīng)顟B(tài)
• 適當(dāng)?shù)呐渲酶?/li>
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