Add DateTime.Parse, TryParse and Convert.ToDateTime (#169)

Author: josesimoes

Tests/NFUnitTestSystemLib/UnitTestDateTime.cs

@@ -2287,6 +2287,68 @@ public void DateTime_AboveMaxDatTime_ArgumentOutOfRangeExceptionTest59()
             Assert.Throws(typeof(ArgumentOutOfRangeException), () => { DateTime dt2 = new DateTime(10000, 1, 1, 0, 0, 0, 0); });
         }
 
+        [TestMethod]
+        public void DateTime_ParseTest00()
+        {
+            // perform 10 random conversions
+            for (int i = 0; i < 10; i++)
+            {
+                DateTime dt = GetRandomDateTime();
+
+                // UniversalSortableDateTimePattern
+                var specifier1 = "u";
+
+                string dtOutput1 = dt.ToString(specifier1);
+
+                Assert.Equal(DateTime.Parse(dtOutput1).ToString(specifier1), dt.ToString(specifier1), $"DateTime.Parse '{dt}' failed");
+
+                Assert.True(DateTime.TryParse(dtOutput1, out DateTime result), $"DateTime.TryParse '{dt}' failed");
+                Assert.Equal(result.ToString(specifier1), dt.ToString(specifier1), $"DateTime.TryParse '{dt}' returning wrong value: '{result}'");
+            }
+        }
+
+        [TestMethod]
+        public void DateTime_ParseTest01()
+        {
+            // perform 10 random conversions
+            for (int i = 0; i < 10; i++)
+            {
+                DateTime dt = GetRandomDateTime();
+
+                // Round Trip ISO 8601 compatible
+                var specifier1 = "o";
+
+                string dtOutput1 = dt.ToString(specifier1);
+
+                // expected format is yyyy-MM-ddTHH:mm:ss.fffffffK
+                Assert.Equal(DateTime.Parse(dtOutput1).ToString(specifier1), dt.ToString(specifier1), $"Parsing DateTime '{dt}' failed");
+
+                Assert.True(DateTime.TryParse(dtOutput1, out DateTime result), $"DateTime.TryParse '{dt}' failed");
+                Assert.Equal(result.ToString(specifier1), dt.ToString(specifier1), $"DateTime.TryParse '{dt}' returning wrong value: '{result}'");
+            }
+        }
+
+        [TestMethod]
+        public void DateTime_ParseTest02()
+        {
+            // perform 10 random conversions
+            for (int i = 0; i < 10; i++)
+            {
+                DateTime dt = GetRandomDateTime();
+
+                // RFC 1123 date
+                var specifier1 = "r";
+
+                string dtOutput1 = dt.ToString(specifier1);
+
+                // expected format is ddd, dd MMM yyyy HH':'mm':'ss 'GMT'
+                Assert.Equal(DateTime.Parse(dtOutput1).ToString(specifier1), dt.ToString(specifier1), $"Parsing DateTime '{dt}' failed");
+
+                Assert.True(DateTime.TryParse(dtOutput1, out DateTime result), $"DateTime.TryParse '{dt}' failed");
+                Assert.Equal(result.ToString(specifier1), dt.ToString(specifier1), $"DateTime.TryParse '{dt}' returning wrong value: '{result}'");
+            }
+        }
+
         static double[] rdmFraction = new double[] { 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 };
 
         static int year, month, day, hour, minute, second, millisec;

nanoFramework.CoreLibrary/System/Convert.cs

@@ -37,6 +37,9 @@ public static class Convert
         [MethodImpl(MethodImplOptions.InternalCall)]
         internal static extern double NativeToDouble(string value, bool throwException, out bool success);
 
+        [MethodImpl(MethodImplOptions.InternalCall)]
+        internal static extern DateTime NativeToDateTime(string value, bool throwException, out bool success);
+
         /// <summary>
         /// Converts the value of the specified 8-bit unsigned integer to an equivalent Boolean value.
         /// </summary>
@@ -121,6 +124,31 @@ public static byte ToByte(bool value)
             return value ? (byte)1 : (byte)0;
         }
 
+        /// <summary>
+        /// Converts the specified string representation of a date and time to an equivalent date and time value.
+        /// </summary>
+        /// <param name="value">The string representation of a date and time.</param>
+        /// <returns>The date and time equivalent of the value of <paramref name="value"/>, or the date and time equivalent of <see cref="DateTime.MinValue"/> if value is null.</returns>
+        /// <exception cref="FormatException"><paramref name="value"/> is not a properly formatted date and time string.</exception>
+        /// <remarks>
+        /// <para>
+        /// If <paramref name="value"/> is not null, the return value is the result of invoking the <see cref="DateTime.Parse"/> method on value using the formatting information of the Invariant Culture. The <paramref name="value"/> argument must contain the representation of a date and time in one of the formats described in the DateTimeFormatInfo topic. If <paramref name="value"/> is <see langword="null"/>, the method returns <see cref="DateTime.MinValue"/>.
+        /// </para>
+        /// <para>
+        /// This method tries to parse <paramref name="value"/> completely and avoid throwing a <see cref="FormatException"/>. It completes missing month, day, and year information with the current date. If value contains only a date and no time, this method assumes a time of midnight. Any leading, inner, or trailing white-space characters in value are ignored.
+        /// </para>
+        /// <para>
+        /// If you prefer not to handle an exception if the conversion fails, you can call the <see cref="DateTime.TryParse"/> method instead. It returns a <see cref="bool"/> value that indicates whether the conversion succeeded or failed.
+        /// </para>
+        /// </remarks>
+        public static DateTime ToDateTime(string value)
+        {
+            return NativeToDateTime(
+                value,
+                true,
+                out _);
+        }
+
         /// <summary>
         /// Converts the specified string representation of a number to an equivalent 16-bit signed integer.
         /// </summary>

nanoFramework.CoreLibrary/System/DateTime.cs

@@ -787,6 +787,53 @@ public override int GetHashCode()
 
         }
 
+        /// <summary>
+        /// Converts the string representation of a date and time to its <see cref="DateTime"/> equivalent by using the conventions of the current culture.
+        /// </summary>
+        /// <param name="s">A string that contains a date and time to convert. See The string to parse for more information.</param>
+        /// <returns>An object that is equivalent to the date and time contained in <paramref name="s"/>.</returns>
+        /// <exception cref="ArgumentNullException"><paramref name="s"/> is <see langword="null"/>.</exception>
+        /// <exception cref="FormatException">Failed to parse <paramref name="s"/>.</exception>
+        /// <remarks>
+        /// <para>
+        /// .NET nanoFramework doesn't support local times so converted values will always have <see cref="Kind"/> set to <see cref="DateTimeKind.Utc"/>.
+        /// </para>
+        /// <para>
+        /// This attempts to parse <paramref name="s"/> by using the formatting conventions of Invariant Culture.
+        /// </para>
+        /// </remarks>
+        public static DateTime Parse(string s)
+        {
+            // check for null string is carried out in native code
+            return Convert.ToDateTime(s);
+        }
+
+        /// <summary>
+        /// Converts the specified string representation of a date and time to its <see cref="DateTime"/> equivalent and returns a value that indicates whether the conversion succeeded.
+        /// </summary>
+        /// <param name="s">A string containing a date and time to convert.</param>
+        /// <param name="result">When this method returns, contains the <see cref="DateTime"/> value equivalent to the date and time contained in <paramref name="s"/>, if the conversion succeeded, or <see cref="MinValue"/> if the conversion failed. The conversion fails if the <paramref name="s"/> parameter is <see langword="null"/>, is an <see cref="string.Empty"/>, or does not contain a valid string representation of a date and time. This parameter is passed uninitialized.</param>
+        /// <returns><see langword="true"/> if the <paramref name="s"/> parameter was converted successfully; otherwise, <see langword="false"/>.</returns>
+        /// <remarks>
+        /// <para>
+        /// The <see cref="TryParse"/> method is similar to the <see cref="Parse"/> method, except that the <see cref="TryParse"/> method does not throw an exception if the conversion fails.
+        /// </para>
+        /// <para>
+        /// The string <paramref name="s"/> is parsed using formatting information of the Invariant Culture.
+        /// </para>
+        /// </remarks>
+        public static bool TryParse(
+            string s,
+            out DateTime result)
+        {
+            result = Convert.NativeToDateTime(
+                s,
+                false,
+                out bool success);
+
+            return success;
+        }
+
         [DebuggerBrowsable(DebuggerBrowsableState.Never)]
         private string DateTimeDisplay => $"{{{new DateTime(Ticks).ToString()}}}";
 

nanoFramework.CoreLibrary/System/Double.cs

@@ -181,7 +181,7 @@ public static bool TryParse(
         {
             result = Convert.NativeToDouble(
               s,
-              true,
+              false,
               out bool success);
 
             return success;