[NUI] Fix null exception in Loading and improve code (#2478)

This fixes null pointer exception in Loading when running following sample,

```C#
var loading1 = new Loading(new LoadingStyle
{
    Size = new Size(100, 100),
    Position = new Position(0, 100),
    Images  = imageArray
});
```

Plus, this patch removes redundant behaviors when applying a style to a Loading component.
All components copies a default style to the component properties when it is created.
When copying a style, all bindable properties defined in the style class that is not null value are copied to the component properties,
so it is important to keep null value for the property that is not set by user.
Hence this patch removes code that allocates empty list object in the getter of ImageList bindable property.

Signed-off-by: Jiyun Yang <ji.yang@samsung.com>
Co-authored-by: Seoyeon2Kim <34738918+Seoyeon2Kim@users.noreply.github.com>

diff --git a/src/Tizen.NUI.Components/Controls/Loading.cs b/src/Tizen.NUI.Components/Controls/Loading.cs
index c61528a..2e192f8 100755 (executable)
--- a/src/Tizen.NUI.Components/Controls/Loading.cs
+++ b/src/Tizen.NUI.Components/Controls/Loading.cs
@@ -54,7 +54,7 @@ namespace Tizen.NUI.Components
             {
                 var newValueList = newValue as List<string>;
                 instance.loadingStyle.ImageList = newValueList;
-                instance.imageVisual.URLS = newValueList;
+                if (instance.imageVisual != null) instance.imageVisual.URLS = newValueList;
             }
         },
         defaultValueCreator: (bindable) =>

diff --git a/src/Tizen.NUI.Components/Style/LoadingStyle.cs b/src/Tizen.NUI.Components/Style/LoadingStyle.cs
index a24a54b..49e770c 100755 (executable)
--- a/src/Tizen.NUI.Components/Style/LoadingStyle.cs
+++ b/src/Tizen.NUI.Components/Style/LoadingStyle.cs
@@ -53,16 +53,10 @@ namespace Tizen.NUI.Components
         [EditorBrowsable(EditorBrowsableState.Never)]
         public static readonly BindableProperty ImagesProperty = BindableProperty.Create(nameof(Images), typeof(string[]), typeof(LoadingStyle), null, propertyChanged: (bindable, oldValue, newValue) =>
         {
-            ((LoadingStyle)bindable).images = new List<string>((string[])newValue);
+            ((LoadingStyle)bindable).images = newValue == null ? null : new List<string>((string[])newValue);
         },
-        defaultValueCreator: (bindable) =>
-        {
-            if (((LoadingStyle)bindable).images == null)
-            {
-                ((LoadingStyle)bindable).images = new List<string>();
-            }
-            return ((LoadingStyle)bindable).images?.ToArray();
-        });
+        defaultValueCreator: (bindable) => ((LoadingStyle)bindable).images?.ToArray()
+        );
 
         /// <summary>The Images bindable property.</summary>
         [EditorBrowsable(EditorBrowsableState.Never)]
@@ -70,14 +64,8 @@ namespace Tizen.NUI.Components
         {
             ((LoadingStyle)bindable).images = newValue as List<string>;
         },
-        defaultValueCreator: (bindable) =>
-        {
-            if(((LoadingStyle)bindable).images == null)
-            {
-                ((LoadingStyle)bindable).images = new List<string>();
-            }
-            return ((LoadingStyle)bindable).images;
-        });
+        defaultValueCreator: (bindable) => ((LoadingStyle)bindable).images
+        );
 
         private Selector<int?> frameRate;
         private List<string> images;
@@ -105,7 +93,7 @@ namespace Tizen.NUI.Components
         /// <since_tizen> 8 </since_tizen>
         public string[] Images
         {
-            get => (string[])GetValue(ImagesProperty);
+            get => (ImageList as List<string>)?.ToArray();
             set => SetValue(ImagesProperty, value);
         }
 
@@ -115,7 +103,14 @@ namespace Tizen.NUI.Components
         [EditorBrowsable(EditorBrowsableState.Never)]
         public IList<string> ImageList
         {
-            get => GetValue(ImageListProperty) as List<string>;
+            get
+            {
+                if (images == null)
+                {
+                    images = new List<string>();
+                }
+                return GetValue(ImageListProperty) as List<string>;
+            }
             internal set => SetValue(ImageListProperty, value);
         }