每当 Kotlin 中的 arraylist 发生更改时如何更新 textview

Question

我在 activity_main 文件中有 textview 和 arraylist，并且我想在发生更改时更改 TextView 的文本值。

class MainActivity : AppCompatActivity(){

var list = ArrayList<Product>()


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

我知道如何通过单击按钮来实现，但我希望它以一种方式绑定或连接，只要数组列表中发生更改，textview 就应该立即反映更改。

谢谢

Answer 1

LiveData 用于需要根据可观察状态自动更新视图的情况。

class MainActivity : AppCompatActivity(){

    // this live data holds the state of your view
    val productsLiveData = MutableLiveData<List<Product>>()

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

        // initialize state with an empty list
        productsLiveData.value = ArrayList()

        // register an observer to be notified on every state change.
        productsLiveData.observe(this, Observer{
            //here you should bind state to view
            myTextView.text = it.joinToString(", ")
        })
    }

    fun updateList(product: Product){
        val oldProducts = productsLiveData.value
        val newProducts = oldProducts + product
        // update live data value, so observers will automatically be notified
        productsLiveData.value = newProducts 
    }
}

每当 Kotlin 中的 arraylist 发生更改时如何更新 textview

how to update textview whenever changes happen in arraylist in Kotlin

android

arraylist

textview

kotlin