Refactor PartAttachmentWidget

- Now displays generic attachments
- Augment the InvenTreeAttachment class to "know" about its model reference

lib/widget/attachment_widget.dart

@@ -0,0 +1,140 @@
+/*
+ * A generic widget for displaying a list of attachments.
+ *
+ * To allow use with different "types" of attachments,
+ * we pass a subclassed instance of the InvenTreeAttachment model.
+ */
+
+import "dart:io";
+
+import "package:flutter/material.dart";
+import "package:font_awesome_flutter/font_awesome_flutter.dart";
+import "package:inventree/inventree/model.dart";
+import "package:inventree/widget/fields.dart";
+import "package:inventree/widget/snacks.dart";
+import "package:inventree/widget/refreshable_state.dart";
+import "package:inventree/l10.dart";
+
+class AttachmentWidget extends StatefulWidget {
+
+  const AttachmentWidget(this.attachment, this.referenceId, this.hasUploadPermission) : super();
+
+  final InvenTreeAttachment attachment;
+  final int referenceId;
+  final bool hasUploadPermission;
+
+  @override
+  _AttachmentWidgetState createState() => _AttachmentWidgetState(attachment, referenceId, hasUploadPermission);
+}
+
+
+class _AttachmentWidgetState extends RefreshableState<AttachmentWidget> {
+
+  _AttachmentWidgetState(this.attachment, this.referenceId, this.hasUploadPermission);
+
+  final InvenTreeAttachment attachment;
+  final int referenceId;
+  final bool hasUploadPermission;
+
+  List<InvenTreeAttachment> attachments = [];
+
+  @override
+  String getAppBarTitle(BuildContext context) => L10().attachments;
+
+  @override
+  List<Widget> getAppBarActions(BuildContext context) {
+
+    List<Widget> actions = [];
+
+    if (hasUploadPermission) {
+      // File upload
+      actions.add(
+          IconButton(
+            icon: FaIcon(FontAwesomeIcons.plusCircle),
+            onPressed: () async {
+              FilePickerDialog.pickFile(
+                  onPicked: (File file) {
+                    upload(file);
+                  }
+              );
+            },
+          )
+      );
+    }
+
+    return actions;
+  }
+
+  Future<void> upload(File file) async {
+
+    final bool result = await attachment.uploadAttachment(file, referenceId);
+
+    if (result) {
+      showSnackIcon(L10().uploadSuccess, success: true);
+    } else {
+      showSnackIcon(L10().uploadFailed, success: false);
+    }
+
+    refresh(context);
+  }
+
+  @override
+  Future<void> request(BuildContext context) async {
+
+    await attachment.list(
+      filters: {
+        attachment.REFERENCE_FIELD: referenceId.toString()
+      }
+    ).then((var results) {
+
+      attachments.clear();
+
+      for (var result in results) {
+        if (result is InvenTreeAttachment) {
+          attachments.add(result);
+        }
+      }
+    });
+  }
+
+  @override
+  Widget getBody(BuildContext context) {
+    return Center(
+        child: ListView(
+          children: ListTile.divideTiles(
+              context: context,
+              tiles: attachmentTiles(context)
+          ).toList(),
+        )
+    );
+  }
+
+
+  List<Widget> attachmentTiles(BuildContext context) {
+
+    List<Widget> tiles = [];
+
+    for (var attachment in attachments) {
+      tiles.add(ListTile(
+        title: Text(attachment.filename),
+        subtitle: Text(attachment.comment),
+        leading: FaIcon(attachment.icon),
+        onTap: () async {
+          await attachment.downloadAttachment();
+        },
+      ));
+    }
+
+    if (tiles.isEmpty) {
+      tiles.add(ListTile(
+        title: Text(L10().attachmentNone),
+        subtitle: Text(
+          L10().attachmentNonePartDetail,
+          style: TextStyle(fontStyle: FontStyle.italic),
+        ),
+      ));
+    }
+
+    return tiles;
+  }
+}