# 14. Structure View Factory

> For the complete documentation index, see [llms.txt](https://plugins.jetbrains.com/docs/intellij/llms.txt).

> **TL;DR**
> Reference: [Structure View](structure-view.html)
>
>
>
> Code: [SimpleStructureViewFactory](https://github.com/JetBrains/intellij-sdk-code-samples/tree/main/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleStructureViewFactory.java), [SimpleStructureViewModel](https://github.com/JetBrains/intellij-sdk-code-samples/tree/main/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleStructureViewModel.java), [SimpleStructureViewElement](https://github.com/JetBrains/intellij-sdk-code-samples/tree/main/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleStructureViewElement.java)

> **Tip:**
> This page is part of multi-step [Custom Language Support Tutorial](custom-language-support-tutorial.html). All previous steps must be executed in sequence for the code to work.

The structure view can be customized for a specific file type. Creating a structure view factory allows showing the structure of any file in the Structure tool window or by invoking `Navigate | File Structure` for easy navigation between items in the current editor.

## Define a Structure View Factory

The [SimpleStructureViewFactory](https://github.com/JetBrains/intellij-sdk-code-samples/tree/main/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleStructureViewFactory.java) implements [PsiStructureViewFactory](https://github.com/JetBrains/intellij-community/tree/idea/263.7307.200/platform/editor-ui-api/src/com/intellij/lang/PsiStructureViewFactory.java). The `getStructureViewBuilder()` implementation reuses the IntelliJ Platform class [TreeBasedStructureViewBuilder](https://github.com/JetBrains/intellij-community/tree/idea/263.7307.200/platform/editor-ui-api/src/com/intellij/ide/structureView/TreeBasedStructureViewBuilder.java). At this point the project will not compile until `SimpleStructureViewModel` is [implemented below](#define-a-structure-view-model).

```JAVA
final class SimpleStructureViewFactory implements PsiStructureViewFactory {

  @Override
  public StructureViewBuilder getStructureViewBuilder(@NotNull final PsiFile psiFile) {
    return new TreeBasedStructureViewBuilder() {
      @NotNull
      @Override
      public StructureViewModel createStructureViewModel(@Nullable Editor editor) {
        return new SimpleStructureViewModel(editor, psiFile);
      }
    };
  }

}
```

## Define a Structure View Model

The [SimpleStructureViewModel](https://github.com/JetBrains/intellij-sdk-code-samples/tree/main/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleStructureViewModel.java) is created by implementing [StructureViewModel](https://github.com/JetBrains/intellij-community/tree/idea/263.7307.200/platform/editor-ui-api/src/com/intellij/ide/structureView/StructureViewModel.java), which defines the model for data displayed in the standard structure view. It also extends [StructureViewModelBase](https://github.com/JetBrains/intellij-community/tree/idea/263.7307.200/platform/editor-ui-api/src/com/intellij/ide/structureView/StructureViewModelBase.java), an implementation that links the model to a text editor.

```JAVA
public class SimpleStructureViewModel extends StructureViewModelBase implements
    StructureViewModel.ElementInfoProvider {

  public SimpleStructureViewModel(@Nullable Editor editor, PsiFile psiFile) {
    super(psiFile, editor, new SimpleStructureViewElement(psiFile));
  }

  @NotNull
  public Sorter @NotNull [] getSorters() {
    return new Sorter[]{Sorter.ALPHA_SORTER};
  }


  @Override
  public boolean isAlwaysShowsPlus(StructureViewTreeElement element) {
    return false;
  }

  @Override
  public boolean isAlwaysLeaf(StructureViewTreeElement element) {
    return element.getValue() instanceof SimpleProperty;
  }

  @Override
  protected Class<?> @NotNull [] getSuitableClasses() {
    return new Class[]{SimpleProperty.class};
  }

}
```

## Define a Structure View Element

The [SimpleStructureViewElement](https://github.com/JetBrains/intellij-sdk-code-samples/tree/main/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleStructureViewElement.java) implements [StructureViewTreeElement](https://github.com/JetBrains/intellij-community/tree/idea/263.7307.200/platform/editor-ui-api/src/com/intellij/ide/structureView/StructureViewTreeElement.java) and [SortableTreeElement](https://github.com/JetBrains/intellij-community/tree/idea/263.7307.200/platform/editor-ui-api/src/com/intellij/ide/util/treeView/smartTree/SortableTreeElement.java). The `StructureViewTreeElement` represents an element in the Structure View tree model. The `SortableTreeElement` represents an item in a smart tree that allows using text other than the presentable text as a key for alphabetic sorting.

```JAVA
public class SimpleStructureViewElement implements StructureViewTreeElement, SortableTreeElement {

  private final NavigatablePsiElement myElement;

  public SimpleStructureViewElement(NavigatablePsiElement element) {
    this.myElement = element;
  }

  @Override
  public Object getValue() {
    return myElement;
  }

  @Override
  public void navigate(boolean requestFocus) {
    myElement.navigate(requestFocus);
  }

  @Override
  public boolean canNavigate() {
    return myElement.canNavigate();
  }

  @Override
  public boolean canNavigateToSource() {
    return myElement.canNavigateToSource();
  }

  @NotNull
  @Override
  public String getAlphaSortKey() {
    String name = myElement.getName();
    return name != null ? name : "";
  }

  @NotNull
  @Override
  public ItemPresentation getPresentation() {
    ItemPresentation presentation = myElement.getPresentation();
    return presentation != null ? presentation : new PresentationData();
  }

  @Override
  public TreeElement @NotNull [] getChildren() {
    if (myElement instanceof SimpleFile) {
      List<SimpleProperty> properties = PsiTreeUtil.getChildrenOfTypeAsList(myElement, SimpleProperty.class);
      List<TreeElement> treeElements = new ArrayList<>(properties.size());
      for (SimpleProperty property : properties) {
        treeElements.add(new SimpleStructureViewElement((SimplePropertyImpl) property));
      }
      return treeElements.toArray(new TreeElement[0]);
    }
    return EMPTY_ARRAY;
  }

}
```

## Register the Structure View Factory

The `SimpleStructureViewFactory` implementation is registered with the IntelliJ Platform in the plugin configuration file using the [com.intellij.lang.structureViewExtension](https://jb.gg/ipe?extensions=com.intellij.lang.structureViewExtension) extension point .

```XML
<extensions defaultExtensionNs="com.intellij">
  <lang.psiStructureViewFactory
      language="Simple"
      implementationClass="org.intellij.sdk.language.SimpleStructureViewFactory"/>
</extensions>
```

## Run the Project

[Run](creating-plugin-project.html#running-the-plugin) the plugin.

Open the `test.simple` file and open `View | Tool Windows | Structure`. The IDE now supports a structure view of the Simple Language:

![Structure View](images/structure_view.png)