avoid setting underlying values for ui element callbacks

CHANGELOG.md

@@ -57,6 +57,7 @@ Additions
 - Added ScrollBar.MouseDragScrolling
 - Added Panel.ScrollToElement
 - Added ElementHelper.MakeGrid
+- Added Button.AutoDisableCondition
 
 Improvements
 - Allow elements to auto-adjust their size even when their children are aligned oddly

MLEM.Ui/Elements/Button.cs

@@ -1,3 +1,4 @@
+using System;
 using Microsoft.Xna.Framework;
 using Microsoft.Xna.Framework.Graphics;
 using MLEM.Graphics;
@@ -51,8 +52,12 @@ namespace MLEM.Ui.Elements {
         /// <summary>
         /// Set this property to true to mark the button as disabled.
         /// A disabled button cannot be moused over, selected or pressed.
+        /// If this value changes often, consider using <see cref="AutoDisableCondition"/>.
         /// </summary>
-        public virtual bool IsDisabled { get; set; }
+        public virtual bool IsDisabled {
+            get => this.isDisabled || this.AutoDisableCondition?.Invoke(this) == true;
+            set => this.isDisabled = value;
+        }
         /// <summary>
         /// Whether this button's <see cref="Text"/> should be truncated if it exceeds this button's width.
         /// Defaults to false.
@@ -69,12 +74,19 @@ namespace MLEM.Ui.Elements {
         /// If this is true, <see cref="CanBeSelected"/> will be able to return true even if <see cref="IsDisabled"/> is true.
         /// </summary>
         public bool CanSelectDisabled;
+        /// <summary>
+        /// An optional function that can be used to modify the result of <see cref="IsDisabled"/> automatically based on a user-defined condition. This removes the need to disable a button based on a condition in <see cref="Element.OnUpdated"/> or manually.
+        /// Note that, if <see cref="IsDisabled"/>'s underlying value is set to <see langword="true"/> using <see cref="set_IsDisabled"/>, this function's result will be ignored.
+        /// </summary>
+        public Func<Button, bool> AutoDisableCondition;
 
         /// <inheritdoc />
         public override bool CanBeSelected => base.CanBeSelected && (this.CanSelectDisabled || !this.IsDisabled);
         /// <inheritdoc />
         public override bool CanBePressed => base.CanBePressed && !this.IsDisabled;
 
+        private bool isDisabled;
+
         /// <summary>
         /// Creates a new button with the given settings
         /// </summary>

MLEM.Ui/Elements/Image.cs

@@ -30,17 +30,13 @@ namespace MLEM.Ui.Elements {
         /// </summary>
         public TextureRegion Texture {
             get {
-                if (this.GetTextureCallback != null)
-                    this.Texture = this.GetTextureCallback(this);
-                return this.texture;
+                var ret = this.GetTextureCallback?.Invoke(this) ?? this.texture;
+                this.CheckTextureChange(ret);
+                return ret;
             }
             set {
-                if (this.texture != value) {
                 this.texture = value;
-                    this.IsHidden = this.texture == null;
-                    if (this.scaleToImage)
-                        this.SetAreaDirty();
-                }
+                this.CheckTextureChange(value);
             }
         }
         /// <summary>
@@ -75,8 +71,12 @@ namespace MLEM.Ui.Elements {
         /// </summary>
         public float ImageRotation;
 
+        /// <inheritdoc />
+        public override bool IsHidden => base.IsHidden || this.Texture == null;
+
         private bool scaleToImage;
         private TextureRegion texture;
+        private TextureRegion lastTexture;
 
         /// <summary>
         /// Creates a new image with the given settings
@@ -123,6 +123,15 @@ namespace MLEM.Ui.Elements {
             base.Draw(time, batch, alpha, context);
         }
 
+        private void CheckTextureChange(TextureRegion newTexture) {
+            if (this.lastTexture == newTexture)
+                return;
+            var nullChanged = this.lastTexture == null != (newTexture == null);
+            this.lastTexture = newTexture;
+            if (nullChanged || this.scaleToImage)
+                this.SetAreaDirty();
+        }
+
         /// <summary>
         /// A delegate method used for <see cref="Image.GetTextureCallback"/>
         /// </summary>

MLEM.Ui/Elements/Paragraph.cs

@@ -53,20 +53,13 @@ namespace MLEM.Ui.Elements {
         /// </summary>
         public string Text {
             get {
-                this.QueryTextCallback();
-                return this.text;
+                var ret = this.GetTextCallback?.Invoke(this) ?? this.text;
+                this.CheckTextChange(ret);
+                return ret;
             }
             set {
-                if (this.text != value) {
                 this.text = value;
-                    this.SetTextDirty();
-
-                    var force = string.IsNullOrWhiteSpace(this.text);
-                    if (this.forceHide != force) {
-                        this.forceHide = force;
-                        this.SetAreaDirty();
-                    }
-                }
+                this.CheckTextChange(value);
             }
         }
         /// <summary>
@@ -105,12 +98,12 @@ namespace MLEM.Ui.Elements {
         }
 
         /// <inheritdoc />
-        public override bool IsHidden => base.IsHidden || this.forceHide;
+        public override bool IsHidden => base.IsHidden || string.IsNullOrWhiteSpace(this.Text);
 
         private string text;
+        private string lastText;
         private StyleProp<TextAlignment> alignment;
         private StyleProp<GenericFont> regularFont;
-        private bool forceHide = true;
 
         /// <summary>
         /// Creates a new paragraph with the given settings.
@@ -141,7 +134,6 @@ namespace MLEM.Ui.Elements {
 
         /// <inheritdoc />
         public override void Update(GameTime time) {
-            this.QueryTextCallback();
             base.Update(time);
             if (this.TokenizedText != null)
                 this.TokenizedText.Update(time);
@@ -149,7 +141,6 @@ namespace MLEM.Ui.Elements {
 
         /// <inheritdoc />
         public override void Draw(GameTime time, SpriteBatch batch, float alpha, SpriteBatchContext context) {
-            this.QueryTextCallback();
             var pos = this.DisplayArea.Location + new Vector2(this.GetAlignmentOffset(), 0);
             var sc = this.TextScale * this.TextScaleMultiplier * this.Scale;
             var color = this.TextColor.OrDefault(Color.White) * alpha;
@@ -202,9 +193,14 @@ namespace MLEM.Ui.Elements {
                 this.SetAreaDirty();
         }
 
-        private void QueryTextCallback() {
-            if (this.GetTextCallback != null)
-                this.Text = this.GetTextCallback(this);
+        private void CheckTextChange(string newText) {
+            if (this.lastText == newText)
+                return;
+            var emptyChanged = string.IsNullOrWhiteSpace(this.lastText) != string.IsNullOrWhiteSpace(newText);
+            this.lastText = newText;
+            if (emptyChanged)
+                this.SetAreaDirty();
+            this.SetTextDirty();
         }
 
         private float GetAlignmentOffset() {