如何在 Kotlin 中为 EditText addTextChangeListener 构建 lambda 表达式？下面给出一个错误：
passwordEditText.addTextChangedListener { charSequence ->
try {
password = charSequence.toString()
} catch (error: Throwable) {
raise(error)
}
}
【问题讨论】：
标签： android kotlin textview anko
addTextChangedListener() 采用TextWatcher，这是一个具有 3 个方法的接口。只有TextWatcher 只有一种方法，您写的内容才有效。我猜你得到的错误与你的 lambda 没有实现其他两种方法有关。您有 2 个选择。
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) {
}
})
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) }
【讨论】：
fun foo() = ...）
afterTextChanged.invoke(...)而不是afterTextChanged(...)？
添加这个核心ktx依赖
implementation 'androidx.core:core-ktx:1.0.0'
你只需要这样做
passwordEditText.doAfterTextChanged{ }
【讨论】：
有点老了，但是使用 Kotlin Android 扩展你可以做这样的事情：
editTextRequest.textChangedListener {
afterTextChanged {
// Do something here...
}
}
不需要额外的代码，只需添加：
implementation 'androidx.core:core-ktx:1.0.0'
【讨论】：
KAndroid 解决方案完美运行。
implementation "androidx.core:core-ktx:1.2.0" -> edt.addTextChangedListener(afterTextChanged = { /*dosomething*/ })
希望这个Kotlin 示例有助于说明清楚：
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
}
}
有了这个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>
还有这个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
【讨论】：
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) { }
})
【讨论】：
抱歉迟到了！
如果将implementation 'androidx.core:core-ktx:1.1.0' 添加到模块的 build.gradle 文件中，则可以使用
etPlayer1.doOnTextChanged { text, start, count, after -> // Do stuff }
【讨论】：
如果你使用implementation 'androidx.core:core-ktx:1.1.0-alpha05'，你可以使用
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)
【讨论】：
添加核心ktx依赖
implementation 'androidx.core:core-ktx:1.3.0'
你可以像这样简单地实现
edit_text.addTextChangedListener { it: Editable? ->
// Do your stuff here
}
【讨论】：
如果您使用材料 Filled text field 或 Outlined text field，请尝试分别响应文档中提到的输入文本更改：
filledTextField.editText?.doOnTextChanged { inputText, _, _, _ ->
// Respond to input text change
}
和
outlinedTextField.editText?.doOnTextChanged { inputText, _, _, _ ->
// Respond to input text change
}
【讨论】：
另一种选择是KAndroid 库 -
implementation 'com.pawegio.kandroid:kandroid:0.8.7@aar'
那么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，但它还附带了一系列其他有用的扩展，可以消除 Android SDK 中的样板代码。
【讨论】：
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)
}
})
【讨论】：
这看起来很整洁：
passwordEditText.setOnEditorActionListener {
textView, keyCode, keyEvent ->
val DONE = 6
if (keyCode == DONE) {
// your code here
}
false
}
【讨论】：