Kotlin CallBack 如何更具 Kt 风味

在 Kotlin 项目中需要对输入框进行监听时需要写如下监听事件，这不跟 Java 几乎一样嘛，这可一点也不 Kotlin

 binding.etLoginName.addTextChangedListener(object: TextWatcher{
            override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
                TODO("Not yet implemented")
            }

            override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {
                TODO("Not yet implemented")
            }

            override fun afterTextChanged(s: Editable?) {
                TODO("Not yet implemented")
            }

        })

于是乎，我们可以改造一下，用 DSL 的方式来处理，先申明 TextWatcherDSL 类用来处理事件

typealias _beforeTextChanged = (CharSequence?, Int, Int, Int) -> Unit
typealias _onTextChanged = (CharSequence?, Int, Int, Int) -> Unit
typealias _afterTextChanged = (Editable?) -> Unit

class TextWatcherDSL {

    var beforeTextChanged: _beforeTextChanged? = null
    var onTextChanged: _onTextChanged? = null
    var afterTextChanged: _afterTextChanged? = null

    fun beforeTextChanged(beforeTextChanged: _beforeTextChanged){
        this.beforeTextChanged = beforeTextChanged
    }

    fun onTextChanged(onTextChanged: _onTextChanged){
        this.onTextChanged = onTextChanged
    }

    fun afterTextChanged(afterTextChanged: _afterTextChanged){
        this.afterTextChanged = afterTextChanged
    }

}

然后再对 TextView 进行类扩展

inline fun TextView.textChangedListener(block: TextWatcherDSL.() -> Unit){
    val dsl = TextWatcherDSL()
    dsl.block()
    addTextChangedListener(object : TextWatcher{
        override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
            dsl.beforeTextChanged?.invoke(s, start, count, after)
        }

        override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {
            dsl.onTextChanged?.invoke(s, start, before, count)
        }

        override fun afterTextChanged(s: Editable?) {
            dsl.afterTextChanged?.invoke(s)
        }

    })
}

最后我们可以在页面这样调用了

binding.etPassword.textChangedListener {

            onTextChanged { charSequence, i, i2, i3 ->
                logI("onTextChanged："+charSequence.toString())
            }
            
            afterTextChanged {
                logI("afterTextChanged")
            }
            
        }