HelpAttribute.cs

// --------------------------------------------------------------------------------------------------------------------
/// <copyright file="HelpAttribute.cs">
///   <See cref="https://github.com/johnearnshaw/unity-inspector-help"></See>
///   Copyright (c) 2017, John Earnshaw, reblGreen Software Limited
///   <See cref="https://github.com/johnearnshaw/"></See>
///   <See cref="https://bitbucket.com/juanshaf/"></See>
///   <See cref="https://reblgreen.com/"></See>
///   All rights reserved.
///   Redistribution and use in source and binary forms, with or without modification, are
///   permitted provided that the following conditions are met:
///      1. Redistributions of source code must retain the above copyright notice, this list of
///         conditions and the following disclaimer.
///      2. Redistributions in binary form must reproduce the above copyright notice, this list
///         of conditions and the following disclaimer in the documentation and/or other materials
///         provided with the distribution.
///   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
///   EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
///   MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.IN NO EVENT SHALL THE
///   COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
///   EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
///   SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
///   HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
///   TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
///   SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
/// </copyright>
// --------------------------------------------------------------------------------------------------------------------
using System;
using UnityEngine;
#if UNITY_EDITOR
using UnityEditor;
#endif

[AttributeUsage(AttributeTargets.Field, Inherited = true)]
public class HelpAttribute : PropertyAttribute
{
    public readonly string text;

    // MessageType exists in UnityEditor namespace and can throw an exception when used outside the editor.
    // We spoof MessageType at the bottom of this script to ensure that errors are not thrown when
    // MessageType is unavailable.
    public readonly MessageType type;


    /// <summary>
    /// Adds a HelpBox to the Unity property inspector above this field.
    /// </summary>
    /// <param name="text">The help text to be displayed in the HelpBox.</param>
    /// <param name="type">The icon to be displayed in the HelpBox.</param>
    public HelpAttribute(string text, MessageType type = MessageType.Info)
    {
        this.text = text;
        this.type = type;
    }
}

#if UNITY_EDITOR
[CustomPropertyDrawer(typeof(HelpAttribute))]
public class HelpDrawer : PropertyDrawer
{
    // Used for top and bottom padding between the text and the HelpBox border.
    const int paddingHeight = 8;

    // Used to add some margin between the the HelpBox and the property.
    const int marginHeight = 2;

    //  Global field to store the original (base) property height.
    float baseHeight = 0;

    // Custom added height for drawing text area which has the MultilineAttribute.
    float addedHeight = 0;

    /// <summary>
    /// A wrapper which returns the PropertyDrawer.attribute field as a HelpAttribute.
    /// </summary>
    HelpAttribute helpAttribute { get { return (HelpAttribute)attribute; } }

    /// <summary>
    /// A helper property to check for RangeAttribute.
    /// </summary>
    RangeAttribute rangeAttribute
    {
        get
        {
            var attributes = fieldInfo.GetCustomAttributes(typeof(RangeAttribute), true);
            return attributes != null && attributes.Length > 0 ? (RangeAttribute)attributes[0] : null;
        }
    }

    /// <summary>
    /// A helper property to check for MultiLineAttribute.
    /// </summary>
    MultilineAttribute multilineAttribute
    {
        get
        {
            var attributes = fieldInfo.GetCustomAttributes(typeof(MultilineAttribute), true);
            return attributes != null && attributes.Length > 0 ? (MultilineAttribute)attributes[0] : null;
        }
    }


    public override float GetPropertyHeight(SerializedProperty prop, GUIContent label)
    {
        // We store the original property height for later use...
        baseHeight = base.GetPropertyHeight(prop, label);

        // This stops icon shrinking if text content doesn't fill out the container enough.
        float minHeight = paddingHeight * 5;

        // Calculate the height of the HelpBox using the GUIStyle on the current skin and the inspector
        // window's currentViewWidth.
        var content = new GUIContent(helpAttribute.text);
        var style = GUI.skin.GetStyle("helpbox");

        var height = style.CalcHeight(content, EditorGUIUtility.currentViewWidth);

        // We add tiny padding here to make sure the text is not overflowing the HelpBox from the top
        // and bottom.
        height += marginHeight * 2;

        // Since we draw a custom text area with the label above if our property contains the
        // MultilineAttribute, we need to add some extra height to compensate. This is stored in a
        // seperate global field so we can use it again later.
        if (multilineAttribute != null && prop.propertyType == SerializedPropertyType.String)
        {
            addedHeight = 48f;
        }

        // If the calculated HelpBox is less than our minimum height we use this to calculate the returned
        // height instead.
        return height > minHeight ? height + baseHeight + addedHeight : minHeight + baseHeight + addedHeight;
    }


    public override void OnGUI(Rect position, SerializedProperty prop, GUIContent label)
    {
        // We get a local reference to the MultilineAttribute as we use it twice in this method and it
        // saves calling the logic twice for minimal optimization, etc...
        var multiline = multilineAttribute;

        EditorGUI.BeginProperty(position, label, prop);

        // Copy the position out so we can calculate the position of our HelpBox without affecting the
        // original position.
        var helpPos = position;

        helpPos.height -= baseHeight + marginHeight;


        if (multiline != null)
        {
            helpPos.height -= addedHeight;
        }

        // Renders the HelpBox in the Unity inspector UI.
        EditorGUI.HelpBox(helpPos, helpAttribute.text, helpAttribute.type);

        position.y += helpPos.height + marginHeight;
        position.height = baseHeight;


        // If we have a RangeAttribute on our field, we need to handle the PropertyDrawer differently to
        // keep the same style as Unity's default.
        var range = rangeAttribute;

        if (range != null)
        {
            if (prop.propertyType == SerializedPropertyType.Float)
            {
                EditorGUI.Slider(position, prop, range.min, range.max, label);
            }
            else if (prop.propertyType == SerializedPropertyType.Integer)
            {
                EditorGUI.IntSlider(position, prop, (int)range.min, (int)range.max, label);
            }
            else
            {
                // Not numeric so draw standard property field as punishment for adding RangeAttribute to
                // a property which can not have a range :P
                EditorGUI.PropertyField(position, prop, label);
            }
        }
        else if (multiline != null)
        {
            // Here's where we handle the PropertyDrawer differently if we have a MultiLineAttribute, to try
            // and keep some kind of multiline text area. This is not identical to Unity's default but is
            // better than nothing...
            if (prop.propertyType == SerializedPropertyType.String)
            {
                var style = GUI.skin.label;
                var size = style.CalcHeight(label, EditorGUIUtility.currentViewWidth);

                EditorGUI.LabelField(position, label);

                position.y += size;
                position.height += addedHeight - size;

                // Fixed text dissappearing thanks to: http://answers.unity3d.com/questions/244043/textarea-does-not-work-text-dissapears-solution-is.html
                prop.stringValue = EditorGUI.TextArea(position, prop.stringValue);
            }
            else
            {
                // Again with a MultilineAttribute on a non-text field deserves for the standard property field
                // to be drawn as punishment :P
                EditorGUI.PropertyField(position, prop, label);
            }
        }
        else
        {
            // If we get to here it means we're drawing the default property field below the HelpBox. More custom
            // and built in PropertyDrawers could be implemented to enable HelpBox but it could easily make for
            // hefty else/if block which would need refactoring!
            EditorGUI.PropertyField(position, prop, label);
        }

        EditorGUI.EndProperty();
    }
}
#else
    // Replicate MessageType Enum if we are not in editor as this enum exists in UnityEditor namespace.
    // This should stop errors being logged the same as Shawn Featherly's commit in the Github repo but I
    // feel is cleaner than having the conditional directive in the middle of the HelpAttribute constructor.
    public enum MessageType
    {
        None,
        Info,
        Warning,
        Error,
    }
#endif