add TMP_Dropdown extension

Author: TORISOUP

src/UniTask/Assets/Plugins/UniTask/Runtime/External/TextMeshPro/TextMeshProAsyncExtensions.Dropdown.cs

@@ -0,0 +1,43 @@
+#if UNITASK_TEXTMESHPRO_SUPPORT
+
+using System;
+using System.Threading;
+using TMPro;
+
+namespace Cysharp.Threading.Tasks
+{
+    public static partial class TextMeshProAsyncExtensions
+    {
+        public static IAsyncValueChangedEventHandler<int> GetAsyncValueChangedEventHandler(this TMP_Dropdown dropdown)
+        {
+            return new AsyncUnityEventHandler<int>(dropdown.onValueChanged, dropdown.GetCancellationTokenOnDestroy(), false);
+        }
+
+        public static IAsyncValueChangedEventHandler<int> GetAsyncValueChangedEventHandler(this TMP_Dropdown dropdown, CancellationToken cancellationToken)
+        {
+            return new AsyncUnityEventHandler<int>(dropdown.onValueChanged, cancellationToken, false);
+        }
+
+        public static UniTask<int> OnValueChangedAsync(this TMP_Dropdown dropdown)
+        {
+            return new AsyncUnityEventHandler<int>(dropdown.onValueChanged, dropdown.GetCancellationTokenOnDestroy(), true).OnInvokeAsync();
+        }
+
+        public static UniTask<int> OnValueChangedAsync(this TMP_Dropdown dropdown, CancellationToken cancellationToken)
+        {
+            return new AsyncUnityEventHandler<int>(dropdown.onValueChanged, cancellationToken, true).OnInvokeAsync();
+        }
+
+        public static IUniTaskAsyncEnumerable<int> OnValueChangedAsAsyncEnumerable(this TMP_Dropdown dropdown)
+        {
+            return new UnityEventHandlerAsyncEnumerable<int>(dropdown.onValueChanged, dropdown.GetCancellationTokenOnDestroy());
+        }
+
+        public static IUniTaskAsyncEnumerable<int> OnValueChangedAsAsyncEnumerable(this TMP_Dropdown dropdown, CancellationToken cancellationToken)
+        {
+            return new UnityEventHandlerAsyncEnumerable<int>(dropdown.onValueChanged, cancellationToken);
+        }
+    }
+}
+
+#endif