mvvm - 使用TextWatcher获取editText的旧值

Question

我想使用beforeTextWatcher函数获取editText的旧值。
问题是，当我尝试获取此旧值时，返回的值始终为null，请有人帮帮我

val nomTextWatcher: TextWatcher
        get() = object : TextWatcher {
            override fun afterTextChanged(s: Editable?) {

            }

            override fun beforeTextChanged(s: CharSequence?, p1: Int, p2: Int, p3: Int) {
                userUpdateSignup.setNom(s.toString())

            }

            override fun onTextChanged(s: CharSequence?, p1: Int, p2: Int, p3: Int) {
               if(!s.toString().isEmpty())                
  userUpdateSignup.setNom(s.toString())

            }
        }

Answer 1

您不仅可以使用TextWatcher，还必须将值存储到类属性中，然后自己检查它。

private var myFieldValue : String = ""

[...]

val nomTextWatcher: TextWatcher
    get() = object : TextWatcher {
        override fun afterTextChanged(s: Editable?) {        
        }

        override fun beforeTextChanged(s: CharSequence?, p1: Int, p2: Int, p3: Int) {
           userUpdateSignup.setNom(s.toString())
        }

        override fun onTextChanged(s: CharSequence?, p1: Int, p2: Int, p3: Int) {
            // Here you can check differences or what you want
            if(!s.toString().isEmpty())                
                userUpdateSignup.setNom(s.toString())

            // After text changed, you have to store it 
            myFieldValue = s.toString()
        }
    }