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03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/Numeric/SupportDynamicSliderMinValue/SupportDynamicSliderMinValue.md

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+# SupportDynamicSliderMinValue
+
+- **功能描述：** 支持数字输入框上滚动条的最小范围值在Alt按下时被动态改变
+- **使用位置：** UPROPERTY
+- **引擎模块：** Numeric Property
+- **元数据类型：** bool
+- **限制类型：** FVector4
+- **关联项：** [SupportDynamicSliderMaxValue](../SupportDynamicSliderMaxValue.md)
+- **常用程度：** ★
+
+支持数字输入框上滚动条的最小范围值在Alt按下时被动态改变。
+
+- 必须配合UIMin，UIMax使用，因为这样才有滚动条UI
+- 一般情况下滚动条范围是初始设置好的，但该设置支持动态改变。方法是按下Alt拖动鼠标。
+- 普通的float属性等是不支持该meta的，因为普通自动生成的的SPropertyEditorNumeric，没有从property meta中提取SupportDynamicSliderMinValue，因此即使设置了也不会生效。
+- 目前源码中只有继承了FMathStructCustomization的FColorGradingVectorCustomizationBase（对应FVector4）才提取SupportDynamicSliderMinValue，然后自己创建SNumericEntryBox，从而正确的设置SupportDynamicSliderMinValue的值。
+- 因此如果你也想使得自己的结构里的数字属性支持该功能，也需要手动创建Customization，然后在里面手动创建SNumericEntryBox，从而自己设置SupportDynamicSliderMinValue的值。
+
+## 测试代码：
+
+```cpp
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = DynamicSliderTest, meta = (UIMin = "0", UIMax = "1"))
+	FVector4 MyVector4_NoDynamicSlider;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = DynamicSliderTest, meta = (UIMin = "0", UIMax = "1", SupportDynamicSliderMinValue = "true", SupportDynamicSliderMaxValue = "true"))
+	FVector4 MyVector4_SupportDynamicSlider;
+```
+
+## 测试结果：
+
+可以看见MyVector4_NoDynamicSlider并无法更改0-1的滚动条范围。而MyVector4_SupportDynamicSlider在按下Alt同时拖动鼠标后可以改变最小和最大的UI范围。
+
+![DynamicSlider](DynamicSlider.gif)
+
+## 原理：
+
+在SPropertyEditorNumeric里并不会去提取SupportDynamicSliderMinValue该属性，因此默认情况下该值是不生效的。
+
+```cpp
+void SPropertyEditorNumeric<NumericType>::Construct( const FArguments& InArgs, const TSharedRef<FPropertyEditor>& InPropertyEditor )
+{
+	TNumericPropertyParams<NumericType> NumericPropertyParams(Property, MetaDataGetter);
+	ChildSlot
+	[
+		SAssignNew(PrimaryWidget, SNumericEntryBox<NumericType>)
+		// Only allow spinning if we have a single value
+		.AllowSpin(bAllowSpin)
+		.Value(this, &SPropertyEditorNumeric<NumericType>::OnGetValue)
+		.Font(InArgs._Font)
+		.MinValue(NumericPropertyParams.MinValue)
+		.MaxValue(NumericPropertyParams.MaxValue)
+		.MinSliderValue(NumericPropertyParams.MinSliderValue)
+		.MaxSliderValue(NumericPropertyParams.MaxSliderValue)
+		.SliderExponent(NumericPropertyParams.SliderExponent)
+		.Delta(NumericPropertyParams.Delta)
+		// LinearDeltaSensitivity needs to be left unset if not provided, rather than being set to some default
+		.LinearDeltaSensitivity(NumericPropertyParams.GetLinearDeltaSensitivityAttribute())
+		.AllowWheel(bAllowSpin)
+		.WheelStep(NumericPropertyParams.WheelStep)
+		.UndeterminedString(PropertyEditorConstants::DefaultUndeterminedText)
+		.OnValueChanged(this, &SPropertyEditorNumeric<NumericType>::OnValueChanged)
+		.OnValueCommitted(this, &SPropertyEditorNumeric<NumericType>::OnValueCommitted)
+		.OnUndeterminedValueCommitted(this, &SPropertyEditorNumeric<NumericType>::OnUndeterminedValueCommitted)
+		.OnBeginSliderMovement(this, &SPropertyEditorNumeric<NumericType>::OnBeginSliderMovement)
+		.OnEndSliderMovement(this, &SPropertyEditorNumeric<NumericType>::OnEndSliderMovement)
+		.TypeInterface(TypeInterface)
+	];
+	}
+	
+	virtual FReply OnMouseMove(const FGeometry& MyGeometry, const FPointerEvent& MouseEvent) override
+	{
+			if (MouseEvent.IsAltDown())
+			{
+							float DeltaToAdd = (float)MouseEvent.GetCursorDelta().X / SliderWidthInSlateUnits;
+			
+							if (SupportDynamicSliderMaxValue.Get() && (NumericType)InternalValue == GetMaxSliderValue())
+							{
+								ApplySliderMaxValueChanged(DeltaToAdd, false);
+							}
+							else if (SupportDynamicSliderMinValue.Get() && (NumericType)InternalValue == GetMinSliderValue())
+							{
+								ApplySliderMinValueChanged(DeltaToAdd, false);
+							}
+			}
+	}
+```