可拖动分割条在 Unity3D 的编辑器结构中一般都属于最外层结构，因为它是基于 GUI 组件，计算位置的时候必须要很精确，所以跟Layout 流式布局混编会比较乱。这里也推荐作为最外层结构使用。

可拖动的分割条

DEMO

下面是我写的一个演示例子 你可以在Unity中直接运行。

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//
//   		Copyright 2017 KeyleXiao.
//     		Contact : Keyle_xiao@hotmail.com 
//
//     		Licensed under the Apache License, Version 2.0 (the "License");
//     		you may not use this file except in compliance with the License.
//     		You may obtain a copy of the License at
//
//     		http://www.apache.org/licenses/LICENSE-2.0
//
//     		Unless required by applicable law or agreed to in writing, software
//     		distributed under the License is distributed on an "AS IS" BASIS,
//     		WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//     		See the License for the specific language governing permissions and
//     		limitations under the License.
//

using  UnityEditor;
using UnityEngine;

namespace SmartDataViewer.Editor
{
    
    public class ExportWizard:EditorWindow
    {
        [MenuItem("SmartDataViewer/ExportWizard")]
        static public void OpenView()
        {
            var w = CreateInstance<ExportWizard >();
            
            w.minSize = new Vector2(350,250);
            w.maxSize = w.minSize;
            Vector2 pos =new Vector2( Screen.width/2-w.minSize.x,Screen.height/2-w.minSize.y);
            w.position = new Rect(pos,w.minSize);
            
            w.ShowUtility();
        }


        private object rawData { get; set; }

        public void InitRawData(object data)
        {
            rawData = data;
        }
        
        
        
        private Vector2 scrollPos = Vector2.zero;
        float currentScrollViewWidth;
        bool resize = false;
        Rect cursorChangeRect;
        
        void OnEnable(){
            this.position = new Rect(200,200,400,300);
            currentScrollViewWidth = this.position.width/2;
            cursorChangeRect = new Rect(currentScrollViewWidth,0,4f,this.position.height);
        }
     
        void OnGUI(){
            GUILayout.BeginHorizontal();
            
            scrollPos = GUILayout.BeginScrollView(scrollPos,GUILayout.Width(currentScrollViewWidth));
            for(int i=0;i<20;i++)
                GUILayout.Label("test content");
            GUILayout.EndScrollView();
                 
            ResizeScrollView();
            
            GUILayout.Label("right part");
            GUILayout.EndHorizontal();
            Repaint();
        }
     
        private void ResizeScrollView(){
            GUI.DrawTexture(cursorChangeRect,EditorGUIUtility.whiteTexture);
            EditorGUIUtility.AddCursorRect(cursorChangeRect,MouseCursor.ResizeHorizontal);
         
            if( Event.current.type == EventType.MouseDown && cursorChangeRect.Contains(Event.current.mousePosition)){
                resize = true;
            }
            if(resize){
                currentScrollViewWidth = Event.current.mousePosition.x;
                cursorChangeRect.Set(currentScrollViewWidth,cursorChangeRect.y,cursorChangeRect.width,cursorChangeRect.height);
            }
            if(Event.current.type == EventType.MouseUp)
                resize = false;        
        }
        
        
    }
}

解析

这里的GUI仅仅是做了一个表现，最核心的其实是 cursorChangeRect 因为你即使不要这个 GUI 也能在这个 Rect 的位置进行拖动。

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GUI.DrawTexture(cursorChangeRect,EditorGUIUtility.whiteTexture);

在鼠标移动的同时将鼠标当前 x 轴的位置赋前面的一个layout，就会推动后面一个layout. (流式布局)