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Mobile/TP1.dart

+import 'package:flutter/material.dart';
+
+void main() {
+  runApp(const MyApp());
+}
+
+const entryStyle = TextStyle(
+  fontSize: 25,
+  color: Colors.indigo,
+);
+const labelStyle = TextStyle(
+  fontSize: 20,
+  color: Colors.black54,
+);
+
+class MyApp extends StatefulWidget {
+  const MyApp({ Key? key }) : super(key: key);
+  @override
+  _MyAppState createState() => _MyAppState();
+}
+
+class _MyAppState extends State<MyApp> {
+  double _enteredNumber = 0.0;
+  String _startingUnit = '';
+  String _arrivalUnit = '';
+  String? _message = '';
+
+  final Map<String, int> _measureMap = {
+    'meters'      : 0,
+    'kilometers'  : 1,
+    'grams'       : 2,
+    'kilograms'   : 3,
+    'feet'        : 4,
+    'miles'       : 5,
+    'pounds'      : 6,
+    'ounces'      : 7
+  };
+
+  final dynamic _formulas = {
+    '0': [1, 0.001, 0, 0, 3.28084, 0.000621371, 0, 0],
+    '1': [1000, 1, 0, 0, 3280.84, 0.621371, 0, 0],
+    '2': [0, 0, 1, 0.0001, 0, 0, 0.00220462, 0.035274],
+    '3': [0, 0, 1000, 1, 0, 0, 2.20462, 35.274],
+    '4': [0.3048, 0.0003048, 0, 0, 1 , 0.000189394, 0, 0],
+    '5': [1609.34, 1.60934, 0, 0, 5280 , 1, 0, 0],
+    '6': [0, 0, 453.592, 0.453592, 0, 0, 1, 16],
+    '7': [0, 0, 28.3495, 0.0283495, 0, 0, 0.0625, 1 ],
+  };
+
+  @override
+  void initState() {
+    _enteredNumber = 0.0;
+    _startingUnit = _measureMap.keys.first;
+    _arrivalUnit = _measureMap.keys.first;
+    super.initState();
+  }
+
+  void convert(double value, String from, String to) {
+    int numFrom = _measureMap[from] ?? 0;
+    int numTo = _measureMap[to] ?? 0;
+    var multiplier = _formulas[numFrom.toString()][numTo];
+    var result = value * multiplier;
+    String message;
+
+    if (result == 0) {
+      message = 'This conversion cannot be released, please try an other value';
+    }
+    else {
+      message = '${value.toString()} $to\n is equal to\n${result.toString()} $to';
+      setState(() {
+        _message = message;
+      });
+    }
+  }
+
+  // Widgets
+  //============================================================================
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      title: 'Measures convertor',
+      home: Scaffold(
+        appBar: AppBar(
+          title: const Text('Measures convertor'),
+          backgroundColor: Colors.indigo,
+        ),
+        body: Container(
+          padding: const EdgeInsets.symmetric(horizontal: 20),
+          child: Column(
+            children: [
+              const Spacer(),
+              const Text(
+                'Enter a measure to convert :',
+                style: entryStyle,
+              ),
+              TextField(
+                onChanged: (text) {
+                  var vr = double.tryParse(text);
+                  if (vr != null) {
+                    setState(() {
+                      _enteredNumber = vr;
+                    });
+                  }
+                },
+              ),
+              const Spacer(),
+              const Text(
+                'From',
+                style: labelStyle,
+              ),
+              DropdownButton(
+                value: _startingUnit,
+                items: _measureMap.keys.map((String unit) {
+                  return DropdownMenuItem<String>(
+                    value: unit,
+                    child: Text(unit),
+                  );
+                }).toList(),
+                onChanged: (String? unit) {
+                  setState(() {
+                    _startingUnit = unit ?? _measureMap.keys.first;
+                  });
+                },
+              ),
+              const Spacer(),
+              const Text(
+                'to',
+                style: labelStyle,
+              ),
+              DropdownButton(
+                value: _arrivalUnit,
+                items: _measureMap.keys.map((String unit) {
+                  return DropdownMenuItem<String>(
+                    value: unit,
+                    child: Text(unit),
+                  );
+                }).toList(),
+                onChanged: (String? unit) {
+                  setState(() {
+                    _arrivalUnit = unit ?? _measureMap.keys.first;
+                  });
+                },
+              ),
+              const Spacer(
+                flex: 2,
+              ),
+              ElevatedButton(
+                onPressed: () {
+                  if (_enteredNumber == 0) {
+                    return;
+                  }
+                  else {
+                    convert(_enteredNumber, _startingUnit, _arrivalUnit);
+                  }
+                },
+                child: const Text(
+                  'Convert',
+                  style: entryStyle,
+                ),
+              ),
+              const Spacer(),
+              Text(
+                _message ?? '',
+                textAlign: TextAlign.center,
+                style: labelStyle,
+              ),
+              const Spacer(
+                flex: 8,
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+}
+
+