feat: Address CA1820 Rule

src/Avalonia.Controls.DataGrid/DataGridValueConverter.cs

@@ -28,8 +28,8 @@ namespace Avalonia.Controls
         {
             if (targetType != null && targetType.IsNullableType())
             {
-                String strValue = value as String;
-                if (strValue == String.Empty)
+                var strValue = value as string;
+                if (string.IsNullOrEmpty(strValue))
                 {
                     return null;
                 }

src/Avalonia.Controls/AppBuilderBase.cs

@@ -210,9 +210,9 @@ namespace Avalonia.Controls
         {
             var moduleInitializers = from assembly in AppDomain.CurrentDomain.GetAssemblies()
                                      from attribute in assembly.GetCustomAttributes<ExportAvaloniaModuleAttribute>()
-                                     where attribute.ForWindowingSubsystem == ""
+                                     where string.IsNullOrEmpty(attribute.ForWindowingSubsystem)
                                       || attribute.ForWindowingSubsystem == WindowingSubsystemName
-                                     where attribute.ForRenderingSubsystem == ""
+                                     where string.IsNullOrEmpty(attribute.ForRenderingSubsystem)
                                       || attribute.ForRenderingSubsystem == RenderingSubsystemName
                                      group attribute by attribute.Name into exports
                                      select (from export in exports

src/Avalonia.Controls/DateTimePickers/TimePicker.cs

@@ -129,7 +129,7 @@ namespace Avalonia.Controls
             get => _clockIdentifier;
             set
             {
-                if (!(string.IsNullOrEmpty(value) || value == "" || value == "12HourClock" || value == "24HourClock"))
+                if (!(string.IsNullOrEmpty(value) || value == "12HourClock" || value == "24HourClock"))
                     throw new ArgumentException("Invalid ClockIdentifier");
                 SetAndRaise(ClockIdentifierProperty, ref _clockIdentifier, value);
                 SetGrid();

src/Avalonia.Controls/DefinitionBase.cs

@@ -366,7 +366,7 @@ namespace Avalonia.Controls
 
             string id = (string)value;
 
-            if (id != string.Empty)
+            if (!string.IsNullOrEmpty(id))
             {
                 int i = -1;
                 while (++i < id.Length)

src/Avalonia.DesignerSupport/Remote/HtmlTransport/SimpleWebSocketHttpServer.cs

@@ -72,7 +72,7 @@ namespace Avalonia.DesignerSupport.Remote.HtmlTransport
                 while (true)
                 {
                     line = await ReadLineAsync();
-                    if (line == "")
+                    if (string.IsNullOrEmpty(line))
                         break;
                     sp = line.Split(new[] {':'}, 2);
                     headers[sp[0]] = sp[1].TrimStart();

src/Avalonia.X11/X11Structs.cs

@@ -661,7 +661,7 @@ namespace Avalonia.X11 {
 			Type type = ev.GetType ();
 			FieldInfo [] fields = type.GetFields (System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Static | System.Reflection.BindingFlags.Instance);
 			for (int i = 0; i < fields.Length; i++) {
-				if (result != string.Empty) {
+				if (!string.IsNullOrEmpty(result)) {
 					result += ", ";
 				}
 				object value = fields [i].GetValue (ev);

tests/Avalonia.Base.UnitTests/Media/TextFormatting/GraphemeBreakTestDataGenerator.cs

@@ -68,7 +68,7 @@ namespace Avalonia.Visuals.UnitTests.Media.TextFormatting
 
                         var graphemeChars = elements[0].Replace(" × ", " ").Split(' ');
 
-                        var codepoints = graphemeChars.Where(x => x != "" && x != "×")
+                        var codepoints = graphemeChars.Where(x => !string.IsNullOrEmpty(x) && x != "×")
                             .Select(x => Convert.ToInt32(x, 16)).ToList();
 
                         var grapheme = codepoints.ToArray();
@@ -77,10 +77,10 @@ namespace Avalonia.Visuals.UnitTests.Media.TextFormatting
                         {
                             var remainingChars = elements[1].Replace(" × ", " ").Split(' ');
 
-                            var remaining = remainingChars.Where(x => x != "" && x != "×").Select(x => Convert.ToInt32(x, 16)).ToArray();
+                            var remaining = remainingChars.Where(x => !string.IsNullOrEmpty(x) && x != "×").Select(x => Convert.ToInt32(x, 16)).ToArray();
 
                             codepoints.AddRange(remaining);
-                        }                     
+                        }
 
                         var data = new GraphemeBreakData
                         {

tests/Avalonia.Controls.UnitTests/AutoCompleteBoxTests.cs

@@ -99,7 +99,7 @@ namespace Avalonia.Controls.UnitTests
 
                 textbox.Text = String.Empty;
                 Dispatcher.UIThread.RunJobs();
-                Assert.True(control.SearchText == String.Empty);
+                Assert.True(string.IsNullOrEmpty(control.SearchText));
                 Assert.False(control.IsDropDownOpen);
                 Assert.True(closeEvent);
             });

tests/Avalonia.Controls.UnitTests/MaskedTextBoxTests.cs

@@ -559,7 +559,7 @@ namespace Avalonia.Controls.UnitTests
                     Text = "0123456789"
                 };
 
-                Assert.True(target.SelectedText == "");
+                Assert.True(string.IsNullOrEmpty(target.SelectedText));
 
                 target.SelectionStart = 2;
                 target.SelectionEnd = 4;

tests/Avalonia.Controls.UnitTests/TextBoxTests.cs

@@ -473,7 +473,7 @@ namespace Avalonia.Controls.UnitTests
                 
                 target.ApplyTemplate();
 
-                Assert.True(target.SelectedText == "");
+                Assert.True(string.IsNullOrEmpty(target.SelectedText));
 
                 target.SelectionStart = 2;
                 target.SelectionEnd = 4;