Kotlin addTextChangeListener lambda吗？

如何在Kotlin中为EditText addTextChangeListener构建lambda表达式？下面给出了一个错误：

passwordEditText.addTextChangedListener { charSequence  ->
    try {
        password = charSequence.toString()
    } catch (error: Throwable) {
        raise(error)
    }
}

addTextChangedListener()需要一个TextWatcher带有3个方法的接口。如果TextWatcher只有一种方法，则您编写的内容仅适用。我将猜测您得到的错误与您的lambda不实现其他两种方法有关。您有2种选择。

1. 抛弃lambda，只使用一个匿名内部类

    editText.addTextChangedListener(object : TextWatcher {
      override fun afterTextChanged(s: Editable?) {
      }
    
      override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
      }
    
      override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {
      }
    })

2. 创建一个扩展方法，以便您可以使用lambda表达式：

    fun EditText.afterTextChanged(afterTextChanged: (String) -> Unit) {
        this.addTextChangedListener(object : TextWatcher {
          override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
          }
    
          override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {
          }
    
          override fun afterTextChanged(editable: Editable?) {
            afterTextChanged.invoke(editable.toString())
          }
        })
    }

然后像这样使用扩展名：

editText.afterTextChanged { doSomethingWithText(it) }

有点老了，但是使用Kotlin Android扩展，您可以执行以下操作：

editTextRequest.textChangedListener {
            afterTextChanged {
                // Do something here...
            }
}

无需额外的代码，只需添加：

implementation 'androidx.core:core-ktx:1.0.0'

添加此核心ktx依赖性

implementation 'androidx.core:core-ktx:1.0.0'

您只需要做

passwordEditText.doAfterTextChanged{ }

希望此Kotlin示例有助于清楚说明：

class MainFragment : Fragment() {

    private lateinit var viewModel: MainViewModel

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                          savedInstanceState: Bundle?): View {
    val view = inflater.inflate(R.layout.main_fragment, container, false)

    view.user.addTextChangedListener(object : TextWatcher {
        override fun beforeTextChanged(s: CharSequence, start: Int, count: Int, after: Int) {

        }

        override fun onTextChanged(s: CharSequence, start: Int, before: Int, count: Int) {

        }

        override fun afterTextChanged(s: Editable) {
                userLayout.error =
                        if (s.length > userLayout.counterMaxLength) {
                            "Max character length is: ${userLayout.counterMaxLength}"
                        } else null
        }
    })
    return view
}

override fun onActivityCreated(savedInstanceState: Bundle?) {
    super.onActivityCreated(savedInstanceState)
    viewModel = ViewModelProviders.of(this).get(MainViewModel::class.java)
    // TODO: Use the ViewModel
   }
}

使用此XML布局：

<android.support.design.widget.TextInputLayout
    android:id="@+id/userLayout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:counterMaxLength="5"
    app:counterEnabled="true"
    android:hint="user_name">

    <android.support.design.widget.TextInputEditText
        android:id="@+id/user"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
</android.support.design.widget.TextInputLayout>

这Gradle：

android {
    compileSdkVersion 'android-P'
...
}
    api 'com.android.support:design:28.0.0-alpha1'

    implementation 'com.android.support:appcompat-v7:28.0.0-alpha1' // appcompat library

测试一下：

passwordEditText.addTextChangedListener(object:TextWatcher{override fun afterTextChanged(s: Editable?) {

    }

    override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
    }

    override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {

    }

})

如果您使用implementation 'androidx.core:core-ktx:1.1.0-alpha05'可以使用

For android.widget.TextView
TextWatcher 
TextView.doBeforeTextChanged(crossinline action: (text: CharSequence?, start: Int, count: Int, after: Int) -> Unit)
Add an action which will be invoked before the text changed.

TextWatcher 
TextView.doOnTextChanged(crossinline action: (text: CharSequence?, start: Int, count: Int, after: Int) -> Unit)
Add an action which will be invoked when the text is changing.

TextWatcher 
TextView.doAfterTextChanged(crossinline action: (text: Editable?) -> Unit)

https://developer.android.com/reference/kotlin/androidx/core/widget/package-summary#extension-functions

对不起，来晚了！

如果添加implementation 'androidx.core:core-ktx:1.1.0'到模块的build.gradle文件中，则可以使用

etPlayer1.doOnTextChanged { text, start, count, after -> // Do stuff }

另一种选择是KAndroid图书馆-

implementation 'com.pawegio.kandroid:kandroid:0.8.7@aar'

然后你可以做这样的事情...

editText.textWatcher { afterTextChanged { doSomething() } }

显然，使用整个库来解决您的问题是多余的，但是它还附带了一系列其他有用的扩展，这些扩展消除了Android SDK中的样板代码。

您可以使用kotlin的命名参数：

private val beforeTextChangedStub: (CharSequence, Int, Int, Int) -> Unit = { _, _, _, _ -> }
private val onTextChangedStub: (CharSequence, Int, Int, Int) -> Unit = { _, _, _, _ -> }
private val afterTextChangedStub: (Editable) -> Unit = {}

fun EditText.addChangedListener(
        beforeTextChanged: (CharSequence, Int, Int, Int) -> Unit = beforeTextChangedStub,
        onTextChanged: (CharSequence, Int, Int, Int) -> Unit = onTextChangedStub,
        afterTextChanged: (Editable) -> Unit = afterTextChangedStub
) = addTextChangedListener(object : TextWatcher {
    override fun beforeTextChanged(charSequence: CharSequence, i: Int, i1: Int, i2: Int) {
        beforeTextChanged(charSequence, i, i1, i2)
    }

    override fun onTextChanged(charSequence: CharSequence, i: Int, i1: Int, i2: Int) {
        onTextChanged(charSequence, i, i1, i2)
    }

    override fun afterTextChanged(editable: Editable) {
        afterTextChanged(editable)
    }
})

添加核心ktx依赖项

implementation 'androidx.core:core-ktx:1.3.0'

您可以像这样简单地实现

    edit_text.addTextChangedListener { it: Editable? ->
      // Do your stuff here
    }

这看起来很整洁：

passwordEditText.setOnEditorActionListener { 
    textView, keyCode, keyEvent ->
    val DONE = 6

    if (keyCode == DONE) {                       
         // your code here
    }
    false
}