Add combo box control

Combo box is a text field with a dropdown that can enter values in the
text field

COM3D2.MeidoPhotoStudio.Plugin/MeidoPhotoStudio/GUI/Controls/ComboBox.cs

@@ -0,0 +1,59 @@
+using System;
+using UnityEngine;
+
+namespace COM3D2.MeidoPhotoStudio.Plugin
+{
+    internal class ComboBox : BaseControl
+    {
+        private TextField textField = new TextField();
+        public Dropdown BaseDropDown { get; private set; }
+        public string Value
+        {
+            get => textField.Value;
+            set => textField.Value = value;
+        }
+
+        public ComboBox(string[] itemList)
+        {
+            this.BaseDropDown = new Dropdown("▾", itemList);
+            this.BaseDropDown.SelectionChange += (s, a) => textField.Value = BaseDropDown.SelectedItem;
+            this.Value = itemList[0];
+        }
+
+        public void SetDropdownItems(string[] itemList)
+        {
+            string oldValue = this.Value;
+            BaseDropDown.SetDropdownItems(itemList);
+            this.Value = oldValue;
+        }
+
+        public void SetDropdownItem(int index, string newItem) => BaseDropDown.SetDropdownItem(index, newItem);
+
+        public void SetDropdownItem(string newItem) => BaseDropDown.SetDropdownItem(newItem);
+
+        public void Draw(float buttonSize, GUIStyle textFieldStyle, params GUILayoutOption[] layoutOptions)
+        {
+            GUILayout.BeginHorizontal();
+            textField.Draw(textFieldStyle, layoutOptions);
+            GUIStyle buttonStyle = new GUIStyle(GUI.skin.button);
+            buttonStyle.alignment = TextAnchor.MiddleCenter;
+            BaseDropDown.Draw(buttonStyle, GUILayout.Width(buttonSize), GUILayout.Height(buttonSize));
+            GUILayout.EndHorizontal();
+        }
+
+        public void Draw(float buttonSize, params GUILayoutOption[] layoutOptions)
+        {
+            Draw(buttonSize, new GUIStyle(GUI.skin.textField), layoutOptions);
+        }
+
+        public override void Draw(params GUILayoutOption[] layoutOptions)
+        {
+            GUILayout.BeginHorizontal();
+            textField.Draw(new GUIStyle(GUI.skin.textField), layoutOptions);
+            GUIStyle buttonStyle = new GUIStyle(GUI.skin.button);
+            buttonStyle.alignment = TextAnchor.MiddleCenter;
+            BaseDropDown.Draw(buttonStyle, GUILayout.ExpandWidth(false));
+            GUILayout.EndHorizontal();
+        }
+    }
+}