Android ListView的事件监听

1、数据项点击事件，针对的是ListView每个数据项的点击事件

listView.setOnItemClickListener { _, _, position, _ ->
    Toast.makeText(this, "position: $position", Toast.LENGTH_LONG).show()
}

2、ListView组件焦点事件（不是指单个item，是整个ListView）

listView.setOnFocusChangeListener { _, hasFocus ->
    if (hasFocus) {
        Log.d("MainActivity", "has focus ... ")
    } else {
        Log.d("MainActivity", "lose focus ...")
    }
}

3、ListView中数据项被选中事件监听

bind.listView.onItemSelectedListener = object: AdapterView.OnItemSelectedListener{
    override fun onItemSelected(parent: AdapterView<*>?,view: View?,position: Int,id: Long) {
        Log.d("MainActivity", "position: $position")
    }

    override fun onNothingSelected(parent: AdapterView<*>?) {
        Log.d("MainActivity", "onNothingSelected ...")
    }
}

AdapterView.OnItemSelectedListener中有两个方法，onItemSelected在数据项被选中时触发，onNothingSelected在LiveView没有任何数据项被选中时触发。

4、监听ListView中item焦点的变化

假设有一个需求，item获取焦点背景颜色为blue，没有焦点的背景颜色为white，则伪代码如下：

Adapter中代码

class FruitAdapter(activity: Activity, private val resourceId: Int, data: List<Fruit>):
    ArrayAdapter<Fruit>(activity, resourceId, data) {

    var position: Int = 0

    override fun getView(position: Int, convertView: View?, parent: ViewGroup): View {
        Log.d("FruitAdapter", "position: $position  convertView: $convertView")
        val view = ... //加载布局伪代码
        if (this.position == position) {
            view.setBackgroundColor(Color.BLUE)
        } else {
            view.setBackgroundColor(Color.WHITE)
        }
        return view
    }
}

Adapter中定义了一个position，用来记录当前哪个item被选中，数值由Activity那边监听更新

MainActivity中代码

override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val bind = ActivityMainBinding.inflate(layoutInflater)
        setContentView(bind.root)
        val fruitAdapter = FruitAdapter(this, R.layout.fruit_item, fruitList)
        bind.listView.adapter = fruitAdapter
        bind.listView.onItemSelectedListener = object: AdapterView.OnItemSelectedListener{
            override fun onItemSelected(parent: AdapterView<*>?,view: View?,position: Int,id: Long) {
                Log.d("MainActivity", "position: $position")
                fruitAdapter.position = position
                fruitAdapter.notifyDataSetChanged()
            }

            override fun onNothingSelected(parent: AdapterView<*>?) {
                Log.d("MainActivity", "onNothingSelected ...")
            }
        }
    }

看红色代码即可，获取ListView对象后，添加onItemSelectedListener 监听，然后把选中的item下标传递给Adapter。这时调用Adapter的方法notifyDataSetChanged()来通知Adapter刷新数据，再次执行Adapter中getView()方法，在getView方法中对下标进行了比较，相等下标的view背景色变为blue，否则变为while，这样就实现了ListView中item焦点变化事件的监听。