114 lines
4.8 KiB
Markdown
114 lines
4.8 KiB
Markdown
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# UseComponentPicker
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- **功能描述：** 用在ComponentReference属性上，使得选取器的列表里展示出Actor属下的Component以便选择。
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- **使用位置：** UPROPERTY
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- **引擎模块：** Component Property
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- **元数据类型：** bool
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- **限制类型：** FComponentReference，FSoftComponentReference
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- **关联项：** [AllowAnyActor](../AllowAnyActor.md)
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- **常用程度：** ★★
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用在ComponentReference属性上，使得选取器的列表里展示出Actor属下的Component以便选择。
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- 默认情况下，FComponentReference的Referenced Actor属性展开的选择器列表是让你选择场景里的Actor，因此并不会把该Actor下的组件也都显示出来。而ComponentReference下的ComponentName属性需要玩家手动填写。这种方式比较原始，也容易出错。
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- 因此加上UseComponentPicker后，就可以显示出组件列表来选择。但是又默认限制是当前Actor属下的所有组件，不包括场景里其他Actor里的组件。
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- 如果想要进一步把场景里所有Actor下的所有组件都列出来，则需要进一步加上AllowAnyActor，以扩大筛选范围。
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- ComponentReference的属性类型有两种，FComponentReference和FSoftComponentReference，二者都对应了FComponentReferenceCustomization。测试代码为简洁就没有列出FSoftComponentReference。
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## 测试代码：
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```cpp
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UPROPERTY(EditInstanceOnly, BlueprintReadWrite, Category = "UseComponentPickerTest")
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FComponentReference MyComponentReference_NoUseComponentPicker;
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UPROPERTY(EditInstanceOnly, BlueprintReadWrite, Category = "UseComponentPickerTest", meta = (UseComponentPicker))
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FComponentReference MyComponentReference_UseComponentPicker;
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UPROPERTY(EditInstanceOnly, BlueprintReadWrite, Category = "UseComponentPicker_AllowAnyActor_Test", meta = (UseComponentPicker,AllowAnyActor))
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FComponentReference MyComponentReference_UseComponentPicker_AllowAnyActor;
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```
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## 测试效果：
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- 可见默认的第一个列出了所有Actor，但是ComponentName需要手写。
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- 第二个加上UseComponentPicker后，列出了当前Actor下的所有组件，但是不能选择到其他Actor的组件。
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- 第三个继续加上AllowAnyActor后，列出了所有Actor的所有组件。
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## 原理:
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FComponentReference和FSoftComponentReference，二者都对应了FComponentReferenceCustomization。看源码可发现用上bUseComponentPicker后，会专门创建ClassFilters和ComboBox，就是采用不同的类型过滤器和不同的UI来选择组件。否则else分支就是很朴素的结构属性展开编辑。
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```cpp
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void FComponentReferenceCustomization::CustomizeHeader(TSharedRef<IPropertyHandle> InPropertyHandle, FDetailWidgetRow& HeaderRow, IPropertyTypeCustomizationUtils& CustomizationUtils)
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{
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PropertyHandle = InPropertyHandle;
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CachedComponent.Reset();
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CachedFirstOuterActor.Reset();
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CachedPropertyAccess = FPropertyAccess::Fail;
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bAllowClear = false;
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bAllowAnyActor = false;
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bUseComponentPicker = PropertyHandle->HasMetaData(NAME_UseComponentPicker);
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bIsSoftReference = false;
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if (bUseComponentPicker)
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{
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FProperty* Property = InPropertyHandle->GetProperty();
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check(CastField<FStructProperty>(Property) &&
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(FComponentReference::StaticStruct() == CastFieldChecked<const FStructProperty>(Property)->Struct ||
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FSoftComponentReference::StaticStruct() == CastFieldChecked<const FStructProperty>(Property)->Struct));
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bAllowClear = !(InPropertyHandle->GetMetaDataProperty()->PropertyFlags & CPF_NoClear);
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bAllowAnyActor = InPropertyHandle->HasMetaData(NAME_AllowAnyActor);
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bIsSoftReference = FSoftComponentReference::StaticStruct() == CastFieldChecked<const FStructProperty>(Property)->Struct;
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BuildClassFilters();
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BuildComboBox();
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InPropertyHandle->SetOnPropertyValueChanged(FSimpleDelegate::CreateSP(this, &FComponentReferenceCustomization::OnPropertyValueChanged));
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// set cached values
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{
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CachedComponent.Reset();
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CachedFirstOuterActor = GetFirstOuterActor();
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FComponentReference TmpComponentReference;
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CachedPropertyAccess = GetValue(TmpComponentReference);
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if (CachedPropertyAccess == FPropertyAccess::Success)
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{
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CachedComponent = TmpComponentReference.GetComponent(CachedFirstOuterActor.Get());
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if (!IsComponentReferenceValid(TmpComponentReference))
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{
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CachedComponent.Reset();
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}
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}
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}
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HeaderRow.NameContent()
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[
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InPropertyHandle->CreatePropertyNameWidget()
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]
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.ValueContent()
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[
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ComponentComboButton.ToSharedRef()
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]
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.IsEnabled(MakeAttributeSP(this, &FComponentReferenceCustomization::CanEdit));
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}
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else
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{
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HeaderRow.NameContent()
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[
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InPropertyHandle->CreatePropertyNameWidget()
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]
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.ValueContent()
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[
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InPropertyHandle->CreatePropertyValueWidget()
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]
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.IsEnabled(MakeAttributeSP(this, &FComponentReferenceCustomization::CanEdit));
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}
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}
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```
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