Fix attach file action from contextmenu (#3084)

* Fix attach file action from contextmenu
Return new ArrayList instead of unmodiefable emptyList()

* Add unit test

* always return ArrayList

* Add javadoc comment

* change to early return

* fix checkstyle

Author: Siedlerchr

CHANGELOG.md

@@ -25,6 +25,7 @@ We refer to [GitHub issues](https://github.com/JabRef/jabref/issues) by using `#
 - We fixed an issue where the preferences could not be imported without a restart of JabRef [#3064](https://github.com/JabRef/jabref/issues/3064)
 - We fixed an issue where <kbd>DEL</kbd>, <kbd>Ctrl</kbd>+<kbd>C</kbd>, <kbd>Ctrl</kbd>+<kbd>V</kbd> and <kbd>Ctrl</kbd>+<kbd>A</kbd> in the search field triggered corresponding actions in the main table [#3067](https://github.com/JabRef/jabref/issues/3067)
 - We fixed an issue where JabRef freezed when editing an assigned file in the `General`-Tab [#2930, comment](https://github.com/JabRef/jabref/issues/2930#issuecomment-311050976)
+- We fixed an issue where a file could not be assigned to an existing entry via the entry context menu action `Attach file` [#3080](https://github.com/JabRef/jabref/issues/3080)
 ### Removed
 
 

src/main/java/org/jabref/gui/filelist/AttachFileAction.java

@@ -15,7 +15,6 @@ public class AttachFileAction implements BaseAction {
 
     private final BasePanel panel;
 
-
     public AttachFileAction(BasePanel panel) {
         this.panel = panel;
     }

src/main/java/org/jabref/gui/filelist/FileListEntryEditor.java

@@ -123,14 +123,12 @@ public class FileListEntryEditor {
 
     private boolean dontOpenBrowseUntilDisposed;
 
-    public FileListEntryEditor(LinkedFile entry, boolean showProgressBar, boolean showOpenButton,
-                               BibDatabaseContext databaseContext, boolean showSaveDialog) {
+    public FileListEntryEditor(LinkedFile entry, boolean showProgressBar, boolean showOpenButton, BibDatabaseContext databaseContext, boolean showSaveDialog) {
         this(entry, showProgressBar, showOpenButton, databaseContext);
         this.showSaveDialog = showSaveDialog;
     }
 
-    public FileListEntryEditor(LinkedFile entry, boolean showProgressBar, boolean showOpenButton,
-                               BibDatabaseContext databaseContext) {
+    public FileListEntryEditor(LinkedFile entry, boolean showProgressBar, boolean showOpenButton, BibDatabaseContext databaseContext) {
         this.entry = entry;
         this.databaseContext = databaseContext;
 

src/main/java/org/jabref/model/entry/BibEntry.java

@@ -1,5 +1,6 @@
 package org.jabref.model.entry;
 
+import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
@@ -802,13 +803,14 @@ public Optional<FieldChange> setFiles(List<LinkedFile> files) {
     /**
      * Gets a list of linked files.
      *
-     * @return the list of linked files, is never null but can be empty
+     * @return the list of linked files, is never null but can be empty.
+     * Changes to the underlying list will have no effect on the entry itself. Use {@link #addFile(LinkedFile)}
      */
     public List<LinkedFile> getFiles() {
         //Extract the path
         Optional<String> oldValue = getField(FieldName.FILE);
         if (!oldValue.isPresent()) {
-            return Collections.emptyList();
+            return new ArrayList<>(); //Return new ArrayList because emptyList is immutable
         }
 
         return FileFieldParser.parse(oldValue.get());

src/main/java/org/jabref/model/entry/FileFieldParser.java

@@ -1,16 +1,17 @@
 package org.jabref.model.entry;
 
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.List;
 
 public class FileFieldParser {
+
     public static List<LinkedFile> parse(String value) {
+        List<LinkedFile> files = new ArrayList<>();
+
         if ((value == null) || value.trim().isEmpty()) {
-            return Collections.emptyList();
+            return files;
         }
 
-        List<LinkedFile> files = new ArrayList<>();
         List<String> entry = new ArrayList<>();
         StringBuilder sb = new StringBuilder();
         boolean inXmlChar = false;

src/test/java/org/jabref/model/entry/BibEntryTest.java

@@ -1,13 +1,18 @@
 package org.jabref.model.entry;
 
+import java.util.Arrays;
+import java.util.List;
 import java.util.Optional;
 
 import org.junit.After;
-import org.junit.Assert;
 import org.junit.Before;
 import org.junit.Test;
 
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+
 public class BibEntryTest {
+
     private BibEntry entry;
 
     @Before
@@ -34,14 +39,22 @@ public void notClearReservedFields() {
     public void getFieldIsCaseInsensitive() throws Exception {
         entry.setField("TeSt", "value");
 
-        Assert.assertEquals(Optional.of("value"), entry.getField("tEsT"));
+        assertEquals(Optional.of("value"), entry.getField("tEsT"));
     }
 
     @Test
     public void clonedBibentryHasUniqueID() throws Exception {
         BibEntry entry = new BibEntry();
         BibEntry entryClone = (BibEntry) entry.clone();
 
-        Assert.assertNotEquals(entry.getId(), entryClone.getId());
+        assertNotEquals(entry.getId(), entryClone.getId());
+    }
+
+    @Test
+    public void testGetAndAddToLinkedFileList() {
+        List<LinkedFile> files = entry.getFiles();
+        files.add(new LinkedFile("", "", ""));
+        entry.setFiles(files);
+        assertEquals(Arrays.asList(new LinkedFile("", "", "")), entry.getFiles());
     }
 }