Unity编辑器扩展——PropertyDrawer

一：前言

PropertyDrawer允许我们自定义一个属性在Inspector面板的如何绘制

二：注意事项

——PropertyDrawer只对可序列化的字段有效
——OnGUI方法里只能使用GUI相关方法（使用EditorGUI绘制），不能使用Layout相关方法

三：代码实现

需要两个类
——定义一个类，继承自PropertyAttribute，为了添加Header时才调用此特性（如果不需要Header则不用定义）
——定义一个类，继承自PropertyDrawer，添加CustomPropertyDrawer标签（不能添加继承MonoBehaviour的类），为了绘制此属性

OnGUI：重写此方法可以自定义此字段在面板上如果绘制。position坐标是从左上角开始
GetPropertyHeight：重写此方法可以指定此字段的GUI像素高度（默认是18）

四：案例——模拟内置的Range特性

using UnityEngine;
using UnityEditor;
using System;
 
public sealed class TestRangeAttribute : PropertyAttribute
{
    public readonly float min;
    public readonly float max;
 
    public TestRangeAttribute(float min, float max)
    {
        this.min = min;
        this.max = max;
    }
}
 
[CustomPropertyDrawer(typeof(TestRangeAttribute))]
public class TestRangeDrawer : PropertyDrawer
{
    public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
    {
        TestRangeAttribute range = attribute as TestRangeAttribute;
 
        if (property.propertyType == SerializedPropertyType.Float)
        {
            EditorGUI.Slider(position, property, range.min, range.max, label);
        }
        else if (property.propertyType == SerializedPropertyType.Integer)
        {
            EditorGUI.IntSlider(position, property, Convert.ToInt32(range.min), Convert.ToInt32(range.max), label);
        }
        else
        {
            EditorGUI.LabelField(position, label.text, "error");
        }
    }
}

五：案例——自定义特性

创建一个自定义的Time特性，可以显示转换成的天、时、分、秒

using UnityEngine;
using UnityEditor;
 
public sealed class TimeAttribute : HeaderAttribute
{
    public bool showDay;
    public bool showHour;
    public bool showMin;
    public bool showSec;
 
    public TimeAttribute(bool showDay = false, bool showHour = false, bool showMin = false, bool showSec = false)
    {
        this.showDay = showDay;
        this.showHour = showHour;
        this.showMin = showMin;
        this.showSec = showSec;
    }
}
 
[CustomPropertyDrawer(typeof(TimeAttribute))]
public class TimeAttributeDrawer : PropertyDrawer
{
    public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
    {
        EditorGUI.PropertyField(new Rect(position.x, position.y, position.width * 0.6f, position.height), property);
        EditorGUI.LabelField(new Rect(position.x + position.width * 0.6f, position.y, position.width * 0.4f, position.height), GetTimeString(property.floatValue));
    }
 
    string GetTimeString(float sec)
    {
        TimeAttribute target = attribute as TimeAttribute;
        if (target.showDay)
        {
            int day = (int)(sec / (60 * 60 * 60));
            return $"{day}天";
        }
        else if (target.showHour)
        {
            int hour = (int)(sec / (60 * 60));
            return $"{hour}小时";
        }
        else if (target.showMin)
        {
            int min = (int)(sec / 60);
            return $"{min}分钟";
        }
        else if (target.showSec)
        {
            return $"{sec}秒";
        }
        else
        {
            return "";
        }
    }
}