使用Lambda创建回调 [英] Create a callback using a lambda

问题描述

我在尝试找出如何使用lambdas在Kotlin中创建回调的过程中遇到了困难.我有一个自定义的TextInputEditText，我想实现一个功能，当文本更改时，活动可以调用该功能.

I'm having a difficult time trying how to figure out how to create a callback in Kotlin using lambdas. I have a custom TextInputEditText and I want to implement a function that the activity can call when text changes.

这是我自定义的EditText:

Here is my custom EditText:

class EditTextEx : TextInputEditText, TextWatcher {
    constructor(context: Context?) : super(context)
    constructor(context: Context?, attrs: AttributeSet?) : super(context, attrs)
    constructor(context: Context?, attrs: AttributeSet?, defStyleAttr: Int) : super(context, attrs, defStyleAttr)


    override fun onTextChanged(s: CharSequence, start: Int, before: Int, count: Int) {
      // Call the callback onTextAvailable with the EditText's text (s.toString)
    }

    override fun afterTextChanged(p0: Editable?) {
    }

    override fun beforeTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {
    }

}

在我的活动中，我希望有一个在调用onTextChanged事件时调用的回调.自定义控件中的回调仅将文本发送回客户端.所以在我的活动中，我想要这样的东西:

In my activity I want to have a callback that gets called when the onTextChanged event gets called. The callback in the custom control sends only the text back to the client. So in my activity, I want something like this:

editText.onTextAvailable(text -> do something )

推荐答案

除了@EpicPandaForce提供的解决方案外，还有其他一些解决方案.如果您要坚持使用示例中所示的类，则可以执行以下操作:

In addition to the solution by @EpicPandaForce, there are a couple other solutions. If you want to stick with using a class as you've shown in your example, then you can do this:

class EditTextEx : TextInputEditText, TextWatcher {
    constructor(context: Context?) : super(context)
    constructor(context: Context?, attrs: AttributeSet?) : super(context, attrs)
    constructor(context: Context?, attrs: AttributeSet?, defStyleAttr: Int) : super(context, attrs, defStyleAttr)

    private var mOnTextWatcherCallback: (m: String) -> Unit = {}

    override fun onTextChanged(s: CharSequence, start: Int, before: Int, count: Int) {
        if (mOnTextWatcherCallback != null)
            mOnTextWatcherCallback(s.toString())
    }

    override fun afterTextChanged(p0: Editable?) {
    }

    override fun beforeTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {
    }

    fun onTextChange(callback: (text: String) -> Unit) {
        mOnTextWatcherCallback = callback
    }
}

然后在您的活动中创建一个函数:

Then in your activity create a function:

fun onTextChange(text: String) {
  // Do something with the text.
}

然后按如下所示设置您的回调:

And then setup your callback as follows:

my_edittext.onTextChange(::onTextChange)

此解决方案使您可以将相同的onTextChange函数重用于其他也要使用它的控件.

This solution allows you to re-use the same onTextChange function for other controls that want to use it as well.

如果您希望使用接口来定义回调，请执行以下操作:

If you prefer to use an interface to define the callback, do this:

class EditTextEx : TextInputEditText, TextWatcher {
    constructor(context: Context?) : super(context)
    constructor(context: Context?, attrs: AttributeSet?) : super(context, attrs)
    constructor(context: Context?, attrs: AttributeSet?, defStyleAttr: Int) : super(context, attrs, defStyleAttr)

    private var mOnTextWatcherCallback: ITextWatcher? = null

    override fun onTextChanged(s: CharSequence, start: Int, before: Int, count: Int) {
        if (mOnTextWatcherCallback != null)
            mOnTextWatcherCallback!!.onTextChanged(s.toString())
    }

    override fun afterTextChanged(p0: Editable?) {
    }

    override fun beforeTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {
    }

    fun onTextChange(callback: ITextWatcher) {
        mOnTextWatcherCallback = callback
    }
}

然后在您的活动中，按如下所示创建回调:

Then in your activity, create the callback as follows:

val textChangeHandler = object: ITextWatcher {
    override fun onTextChanged(text: String) {
        var t = text
    }
}

然后为您的edittext控件设置回调，如下所示:

And then setup your callback for your edittext controls as follows:

my_edittext.onTextChange(textChangeHandler)

这篇关于使用Lambda创建回调的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！