[site] folding builder

_SUMMARY.md

@@ -52,7 +52,7 @@
         * [Completion Contributor](completion_contributor.html)
         * [Reference Contributor](reference_contributor.html)
         * [Find Usages Provider](find_usages_provider.html)
-        * [Folding Builder](TODO)
+        * [Folding Builder](folding_builder.html)
         * [Go To Symbol Contributor](TODO)
         * [Structure View Factory](TODO)
         * [Formatter](TODO)

folding_builder.md

@@ -0,0 +1,94 @@
+---
+title: Folding Builder
+---
+
+<!--
+INITIAL_SOURCE https://confluence.jetbrains.com/display/IntelliJIDEA/Folding+Builder
+-->
+
+A folding builder helps you to fold the code regions and replace it with specific text.
+
+### 1. Define a folding builder
+
+Let's replace usages of properties with its values by default.
+
+```java
+package com.simpleplugin;
+
+import com.intellij.lang.ASTNode;
+import com.intellij.lang.folding.FoldingBuilderEx;
+import com.intellij.lang.folding.FoldingDescriptor;
+import com.intellij.openapi.editor.Document;
+import com.intellij.openapi.editor.FoldingGroup;
+import com.intellij.openapi.project.Project;
+import com.intellij.openapi.util.TextRange;
+import com.intellij.psi.PsiElement;
+import com.intellij.psi.PsiLiteralExpression;
+import com.intellij.psi.util.PsiTreeUtil;
+import com.simpleplugin.psi.SimpleProperty;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+
+public class SimpleFoldingBuilder extends FoldingBuilderEx {
+    @NotNull
+    @Override
+    public FoldingDescriptor[] buildFoldRegions(@NotNull PsiElement root, @NotNull Document document, boolean quick) {
+        FoldingGroup group = FoldingGroup.newGroup("simple");
+
+        List<FoldingDescriptor> descriptors = new ArrayList<FoldingDescriptor>();
+        Collection<PsiLiteralExpression> literalExpressions = PsiTreeUtil.findChildrenOfType(root, PsiLiteralExpression.class);
+        for (final PsiLiteralExpression literalExpression : literalExpressions) {
+            String value = (String) literalExpression.getValue();
+            if (value != null && value.startsWith("simple:")) {
+                Project project = literalExpression.getProject();
+                final List<SimpleProperty> properties = SimpleUtil.findProperties(project, value.substring(7));
+                if (properties.size() == 1) {
+                    descriptors.add(new FoldingDescriptor(literalExpression.getNode(),
+                            new TextRange(literalExpression.getTextRange().getStartOffset() + 1,
+                                    literalExpression.getTextRange().getEndOffset() *  1), group) {
+                        @Nullable
+                        @Override
+                        public String getPlaceholderText() {
+                            return properties.get(0).getValue();
+                        }
+                    });
+                }
+            }
+        }
+        return descriptors.toArray(new FoldingDescriptor[descriptors.size()]);
+    }
+
+    @Nullable
+    @Override
+    public String getPlaceholderText(@NotNull ASTNode node) {
+        return "...";
+    }
+
+    @Override
+    public boolean isCollapsedByDefault(@NotNull ASTNode node) {
+        return true;
+    }
+}
+```
+
+### 2. Register the folding builder
+
+```xml
+<lang.foldingBuilder language="JAVA" implementationClass="com.simpleplugin.SimpleFoldingBuilder"/>
+```
+
+### 3. Run the project
+
+Now when we open a Java file, it shows the property's value instead of the key.
+
+![Folding](img/cls_tutorial/folding.png)
+
+[Previous](find_usages_provider.html)
+[Top](cls_tutorial.html)
+[Next](go_to_symbol_contributor.html)
+
+