Add new formatter to block too many decimals

lib/numeric_formatter.dart

@@ -1,9 +1,9 @@
-import 'package:flutter/services.dart';
+import 'dart:math';
+
 import 'package:flutter/material.dart' show TextField;
+import 'package:flutter/services.dart';
 import 'package:intl/intl.dart';
 
-import 'dart:math';
-
 ///
 /// An implementation of [NumberInputFormatter] automatically inserts thousands
 /// separators to numeric input. For example, a input of `1234` should be
@@ -166,3 +166,81 @@ abstract class NumberInputFormatter extends TextInputFormatter {
   TextEditingValue _formatValue(
       TextEditingValue oldValue, TextEditingValue newValue);
 }
+
+/// Formatter that restricts the number of digits before and after a decimal point
+class DecimalFormatter extends TextInputFormatter {
+  final int decimalCount;
+  final int numberCount;
+  final bool allowNegatives;
+  static final NumberFormat _formatter = NumberFormat.decimalPattern();
+  final NumberFormat formatter;
+
+  DecimalFormatter(
+      {this.decimalCount = 3,
+      this.numberCount = 7,
+      this.formatter,
+      this.allowNegatives = true})
+      : super();
+
+  @override
+  TextEditingValue formatEditUpdate(
+      TextEditingValue oldValue, TextEditingValue newValue) {
+    final _decimalSeparator = (formatter ?? _formatter).symbols.DECIMAL_SEP;
+
+    /// Blank string is allowed
+    if (newValue.text == "") {
+      return newValue;
+    }
+    if (newValue.text.contains("-") && !allowNegatives) {
+      return oldValue;
+    }
+
+    try {
+      /// Check if the number is parseable.  This throws out anything that would make it invalid i.e. alpha characters.
+      final isNotANumber = double.tryParse(newValue.text).isNaN;
+      if (isNotANumber) {
+        return oldValue;
+      }
+    } catch (e) {
+      return oldValue;
+    }
+
+    /// Check how many decimal characters are in the string.  If more than 2, kick it out.
+    final segments = newValue.text.split(_decimalSeparator);
+    final numberOfDecimal = segments.length;
+    if (numberOfDecimal > 2) {
+      return oldValue;
+    } else {
+      /// If we have a decimal
+      if (segments.length == 2) {
+        /// Check that both the number count and decimal pass
+        if (isDecimalPass(segments[1]) && isNumberPass(segments[0])) {
+          return newValue;
+        }
+        return oldValue;
+      } else {
+        /// If we don't have a decimal, just check that the number passes
+        if (isNumberPass(segments[0])) {
+          return newValue;
+        }
+        return oldValue;
+      }
+    }
+  }
+
+  /// checks string against decimal count
+  isDecimalPass(String text) {
+    if (text.length > decimalCount) {
+      return false;
+    }
+    return true;
+  }
+
+  /// checks string against number count
+  isNumberPass(String text) {
+    if (text.length > numberCount) {
+      return false;
+    }
+    return true;
+  }
+}

test/pattern_input_formatter_test.dart

@@ -1,7 +1,6 @@
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:intl/intl.dart';
-
 import 'package:pattern_formatter/pattern_formatter.dart';
 
 void main() {
@@ -17,6 +16,9 @@ _numericFormatterSmokeTest() {
       formatter: NumberFormat.decimalPattern('en_US'), allowFraction: true);
   final CreditCardFormatter creditCardFormatter = CreditCardFormatter();
 
+  final DecimalFormatter decimalFormatterTwoDigits =
+      DecimalFormatter(decimalCount: 2);
+
   test('numeric filter smoke test', () {
     final newValue1 = thousandsFormatter.formatEditUpdate(
         TextEditingValue(
@@ -36,11 +38,36 @@ _numericFormatterSmokeTest() {
         TextEditingValue(
             text: '12a', selection: TextSelection.collapsed(offset: 3)));
 
+    final twoDigitTestCharCheck = decimalFormatterTwoDigits.formatEditUpdate(
+        TextEditingValue(
+            text: '12', selection: TextSelection.collapsed(offset: 2)),
+        TextEditingValue(
+            text: '12a', selection: TextSelection.collapsed(offset: 3)));
+
+    final twoDigitTestCheck = decimalFormatterTwoDigits.formatEditUpdate(
+        TextEditingValue(
+            text: '12', selection: TextSelection.collapsed(offset: 2)),
+        TextEditingValue(
+            text: '12.1', selection: TextSelection.collapsed(offset: 3)));
+
+    final twoDigitTestTooManyDecimalsCheck =
+        decimalFormatterTwoDigits.formatEditUpdate(
+            TextEditingValue(
+                text: '12', selection: TextSelection.collapsed(offset: 2)),
+            TextEditingValue(
+                text: '12.133', selection: TextSelection.collapsed(offset: 3)));
+
     expect(newValue1.text, equals('12'));
 
     expect(newValue2.text, equals('12'));
 
     expect(newValue3.text, equals('12'));
+
+    expect(twoDigitTestCharCheck.text, equals('12'));
+
+    expect(twoDigitTestCheck.text, equals('12.1'));
+
+    expect(twoDigitTestTooManyDecimalsCheck.text, equals('12'));
   });
 
   test('thousands grouping smoke test', () {