问在Android编辑文本中自动添加美元符号($)

EN

private EditText yourEditText;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.main);
    yourEditText = (EditText) findViewById(R.id.yourEditTextId);

    yourEditText.addTextChangedListener(new TextWatcher() {
      @Override
      public void afterTextChanged(Editable s) {
        yourEditText.setText("$" + yourEditText.getText().toString());
      }
      @Override
      public void beforeTextChanged(CharSequence s, int start, int count, int after) {}
      @Override
      public void onTextChanged(CharSequence s, int start, int before, int count) {}
   });
}

 <EditText
        ...
        android:addTextChangedListener="@{viewModel.currencyTextWatcher}"
        android:inputType="number"
        android:digits="$1234567890"
        />

val currencyTextWatcher = object : TextWatcher {
    override fun afterTextChanged(editable: Editable?) {
        when {
            editable.isNullOrEmpty() -> return
            Regex("\\$\\d+").matches(editable.toString()) -> return
            editable.toString() == "$" -> editable.clear()
            editable.startsWith("$").not() -> editable.insert(0, "$")
        }
    }

    override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) = Unit

    override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) = Unit 
}

import android.text.Editable;
import android.text.TextWatcher;
import android.widget.EditText;

import java.text.DecimalFormat;
import java.text.ParseException;

//This class is for entering currency amount while keeping the right format as the user enters values
public class NumberTextWatcher implements TextWatcher {
    private final DecimalFormat dfnd;
    private final EditText et;

    public NumberTextWatcher(EditText editText) {
        dfnd = new DecimalFormat("#,##0.00");
        this.et = editText;
    }

    @Override
    public void afterTextChanged(Editable s) {
        et.removeTextChangedListener(this);
        //After all the text editing, if there is a string to validate - format it
        if (s != null && !s.toString().isEmpty()) {
            try {
                //Take the input string and remove all formatting characters
                String v = s.toString().replace(String.valueOf(df.getDecimalFormatSymbols().getGroupingSeparator()), "").replace("$","").replace(String.valueOf(df.getDecimalFormatSymbols().getDecimalSeparator()), "");
                //Pass the altered string to a number
                Number n = df.parse(v);
                //Get the decimal point correct again
                n = n.doubleValue() / 100.0;
                //Reformat the text with currency symbols, grouping places etc.
                et.setText(dfnd.format(n));
                //Add the Dollar symbol ($)
                et.setText("$".concat(et.getText().toString()));
                //Move the editing cursor back to the right place
                et.setSelection(et.getText().length());

            } catch (NumberFormatException | ParseException e) {
                e.printStackTrace();
            }
        } else //if the input field is empty
        {
            et.setText("$0.00");
        }

        et.addTextChangedListener(this);
    }

    @Override
    public void beforeTextChanged(CharSequence s, int start, int count, int after) {
    }

    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count)
    {
    }
}

TextInputEditText mCashAmount = mView.findViewById(R.id.txtInput_CashAmount);
mCashAmount.addTextChangedListener(new NumberTextWatcher(mCashAmount));