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

/**
 * EditText 限制輸入整數和小數 的位數
 * 默認 整數位無限制，小數位 最多2位
 */
public class DecimalInputTextWatcher implements TextWatcher {

  private static final int DEFAULT_DECIMAL_DIGITS = 2;//默認 小數的位數  2 位

  private EditText editText;
  private int decimalDigits;// 小數的位數
  private int integerDigits;// 整數的位數

  public DecimalInputTextWatcher(EditText editText) {
    this.editText = editText;
    this.decimalDigits = DEFAULT_DECIMAL_DIGITS;
  }

  public DecimalInputTextWatcher(EditText editText, int decimalDigits) {
    this.editText = editText;
    if (decimalDigits <= 0)
      throw new RuntimeException("decimalDigits must > 0");
    this.decimalDigits = decimalDigits;
  }

  public DecimalInputTextWatcher(EditText editText, int integerDigits, int decimalDigits) {
    this.editText = editText;
    if (integerDigits <= 0)
      throw new RuntimeException("integerDigits must > 0");
    if (decimalDigits <= 0)
      throw new RuntimeException("decimalDigits must > 0");
    this.decimalDigits = decimalDigits;
    this.integerDigits = integerDigits;
  }

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

  }

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

  }

  @Override
  public void afterTextChanged(Editable editable) {
    String s = editable.toString();
    editText.removeTextChangedListener(this);

    if (s.contains(".")) {
      if (integerDigits > 0) {
        editText.setFilters(new InputFilter[]{new InputFilter.LengthFilter(integerDigits + decimalDigits + 1)});
      }
      if (s.length() - 1 - s.indexOf(".") > decimalDigits) {
        s = s.substring(0,
            s.indexOf(".") + decimalDigits + 1);
        editable.replace(0, editable.length(), s.trim());//不輸入超出位數的數字
      }
    } else {
      if (integerDigits > 0) {
        editText.setFilters(new InputFilter[]{new InputFilter.LengthFilter(integerDigits + 1)});
        if (s.length() > integerDigits) {
          s = s.substring(0, integerDigits);
          editable.replace(0, editable.length(), s.trim());
        }
      }

    }
    if (s.trim().equals(".")) {//小數點開頭，小數點前補0
      s = "0" + s;
      editable.replace(0, editable.length(), s.trim());
    }
    if (s.startsWith("0") && s.trim().length() > 1) {//多個0開頭，只輸入一個0
      if (!s.substring(1, 2).equals(".")) {
        editable.replace(0, editable.length(), "0");
      }
    }
    editText.addTextChangedListener(this);
  }
}

editText.addTextChangedListener(new DecimalInputTextWatcher(weight, 3, 5));
//限制輸入位數：整數3位，小數點后兩位