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editText.addTextChangedListener(object : TextWatcher {
    override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
        // 文字改變前呼叫
        Log.d("TextWatcher", "beforeTextChanged: $s")
    }

    override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {建立外部類別
        // 文字改變時呼叫
        Log.d("TextWatcher", "onTextChanged: $s")
    }

    override fun afterTextChanged(s: Editable?) {
        // 文字改變後呼叫
        Log.d("TextWatcher", "afterTextChanged: $s")
        
        // 在這裡處理文字改變後的邏輯
        if (s?.length ?: 0 > 10) {
            editText.error = "文字長度不能超過10個字元"
        } else {
            editText.error = null
        }
    }
})

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import android.os.Bundle
import android.util.Log
import android.widget.EditText
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity
import androidx.core.widget.doAfterTextChanged
import androidx.lifecycle.lifecycleScope
import com.example.coroutine.R
import kotlinx.coroutines.channels.awaitClose
import kotlinx.coroutines.flow.callbackFlow
import kotlinx.coroutines.flow.Flow
import kotlinx.coroutines.launch

class TextWatchActivity : AppCompatActivity() {
  private val TAG = "TextWatcher"
  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_textwatch)
    val text_watcher = findViewById<EditText>(R.id.text_watcher)
    lifecycleScope.launch {
      text_watcher.textWatcherFlow()
        .collect { text ->
          Log.d(TAG, "afetr change $text")
        }
    }
  }
  private fun TextView.textWatcherFlow(): Flow<String> = callbackFlow {
    val textWatcher = doAfterTextChanged { editableText ->
      trySend(editableText?.toString() ?: "")
    }
    awaitClose {
      removeTextChangedListener(textWatcher)
    }
  }
}