Breadcrumb bar tweaks

* Fix comments on content provider
* Wire command icons to content provider
* Handle null content of FileSystemView results in the demo

For #8

component/src/desktopMain/kotlin/org/pushingpixels/aurora/component/model/BreadcrumbBarModels.kt

@@ -24,30 +24,27 @@ import java.io.InputStream
  * Content provider for a breadcrumb bar.
  */
 interface BreadcrumbBarContentProvider<T> {
-    /** Returns the display text for the item, or for the root is null is passed. */
+    /** Returns the display text for the item, or for the root is `null` is passed. */
     fun getDisplayText(item: T?): String
 
-    /** Returns the icon for the item, or for the root is null is passed. */
+    /** Returns the icon for the item, or for the root is `null` is passed. */
     fun getIcon(item: T?): Painter? = null
 
     /**
      * Returns the choice elements that correspond to the specified path. If the
-     * path is empty, `null` should be returned. If path is
-     * `null`, the "root" elements should be returned
+     * item is `null`, the list of root elements should be returned.
      *
-     * @param path Breadcrumb bar path.
-     * @return The choice elements that correspond to the specified path
+     * @param item Breadcrumb bar item.
+     * @return The choice elements that correspond to the specified item.
      */
     suspend fun getPathChoices(item: T?): List<T>
 
     /**
-     * Returns the leaf elements that correspond to the specified path. If the
-     * path is empty, `null` should be returned. If path is
-     * `null`, leaf content of the "root" elements should be returned. Most probably, if
-     * your root is more than one element, you should be returning null in here.
+     * Returns the leaf elements that correspond to the specified item. If the specified
+     * item has no leaf elements, empty list should be returned.
      *
-     * @param path Breadcrumb bar path.
-     * @return The leaf elements that correspond to the specified path
+     * @param item Breadcrumb bar item.
+     * @return The leaf elements that correspond to the specified item.
      */
     suspend fun getLeaves(item: T): List<T>
 
@@ -59,9 +56,7 @@ interface BreadcrumbBarContentProvider<T> {
      * @return Input stream with the leaf content. May be `null` if
      * this is not applicable.
      */
-    suspend fun getLeafContent(leaf: T): InputStream? {
-        return null
-    }
+    suspend fun getLeafContent(leaf: T): InputStream? = null
 }
 
 data class BreadcrumbBarPresentationModel(

demo/src/desktopMain/kotlin/org/pushingpixels/aurora/demo/AuroraBreadcrumbBarDemo.kt

@@ -38,7 +38,6 @@ import org.pushingpixels.aurora.window.AuroraWindow
 import org.pushingpixels.aurora.window.AuroraWindowScope
 import org.pushingpixels.aurora.window.auroraApplication
 import java.io.File
-import java.io.InputStream
 import javax.swing.JFileChooser
 import javax.swing.filechooser.FileSystemView
 
@@ -79,10 +78,11 @@ fun AuroraWindowScope.BreadcrumbContent(auroraSkinDefinition: MutableState<Auror
             }
 
             override suspend fun getPathChoices(item: File?): List<File> {
-                // If our path is empty, get the file system roots. Otherwise, get all files under
-                // the last file in the path.
+                // If our item is null, get the file system roots. Otherwise, get all files under
+                // this file item.
                 val candidates =
-                    if (item == null) fileSystemView.roots else item.listFiles()
+                    (if (item == null) fileSystemView.roots else item.listFiles())
+                        ?: return emptyList()
 
                 // Now filter out hidden ones and non-directories, map the rest to
                 // what the content provider needs to return, and sort them by display name
@@ -92,18 +92,15 @@ fun AuroraWindowScope.BreadcrumbContent(auroraSkinDefinition: MutableState<Auror
             }
 
             override suspend fun getLeaves(item: File): List<File> {
-                // Get all files under the last file in the path, filter out hidden ones and
+                // Get all files under the file item, filter out hidden ones and
                 // directory ones, map the rest to what the content provider needs to
                 // return, and sort them by display name
-                return item.listFiles()
+                val candidates = item.listFiles() ?: return emptyList()
+                return candidates
                     .filterNot { it.isDirectory || fileSystemView.isHiddenFile(it) }
                     .map { it }
                     .sortedBy { getDisplayText(it).lowercase() }
             }
-
-            override suspend fun getLeafContent(leaf: File): InputStream? {
-                return null
-            }
         }
 
     val contentModel = remember { mutableStateListOf<Command>() }
@@ -118,7 +115,7 @@ fun AuroraWindowScope.BreadcrumbContent(auroraSkinDefinition: MutableState<Auror
 
         return Command(
             text = this.getDisplayText(item),
-            icon = null,
+            icon = this.getIcon(item),
             action = {
                 // This is called when the path item is clicked
                 while (contentModel.size > level) {
@@ -130,7 +127,7 @@ fun AuroraWindowScope.BreadcrumbContent(auroraSkinDefinition: MutableState<Auror
                 group = CommandGroup(title = null,
                     commands = pathChoices.map { pathChoice ->
                         Command(text = this.getDisplayText(pathChoice),
-                            icon = null,
+                            icon = this.getIcon(pathChoice),
                             action = {
                                 // This is called when a dropdown item is clicked
                                 while (contentModel.size > level) {