update

Packages/app.rive.rive-unity/Runtime/DataBinding/Values/ViewModelInstanceStringProperty.cs

@@ -0,0 +1,64 @@
+using System;
+using System.Runtime.InteropServices;
+
+namespace Rive
+{
+    /// <summary>
+    /// A view model instance property that holds a string.
+    /// </summary>
+    public sealed class ViewModelInstanceStringProperty : ViewModelInstancePrimitiveProperty<string>
+    {
+        [StructLayout(LayoutKind.Sequential)]
+        private struct StringHashInfo
+        {
+            public IntPtr str;
+            public uint length;
+            public uint hash;
+        }
+
+        private StringHashInfo m_lastInfo;
+        private string m_stringVal = null;
+
+        internal ViewModelInstanceStringProperty(IntPtr instanceValuePtr, ViewModelInstance parentInstance) : base(instanceValuePtr, parentInstance)
+        {
+        }
+
+        public override string Value
+        {
+            get
+            {
+                ThrowIfOwnerDisposed();
+                StringHashInfo currentInfo = getViewModelInstanceStringInfo(InstancePropertyPtr);
+
+                // We check if either length or hash changed before marshalling the string
+                // This is a performance optimization to avoid marshalling the string every frame if it hasn't changed as it allocates memory every time the value is read
+                // This allocation can be expensive and might cause GC spikes if done frequently 
+
+                // TODO: Since the VM Instance Runtime knows when the string changes, we should switch to using that instead instead of a hash at some point
+                bool stringHasChanged = currentInfo.length != m_lastInfo.length || currentInfo.hash != m_lastInfo.hash;
+                if (m_stringVal == null || stringHasChanged)
+                {
+                    m_lastInfo = currentInfo;
+
+                    m_stringVal = Marshal.PtrToStringAnsi(currentInfo.str);
+                }
+
+                return m_stringVal;
+            }
+            set
+            {
+                ThrowIfOwnerDisposed();
+                setViewModelInstanceStringValue(InstancePropertyPtr, value);
+            }
+        }
+
+        [DllImport(NativeLibrary.name)]
+        private static extern IntPtr getViewModelInstanceStringValue(IntPtr instanceValue);
+
+        [DllImport(NativeLibrary.name)]
+        private static extern void setViewModelInstanceStringValue(IntPtr instanceValue, string value);
+
+        [DllImport(NativeLibrary.name)]
+        private static extern StringHashInfo getViewModelInstanceStringInfo(IntPtr instanceValue);
+    }
+}