Implement error handling and showing error state

If an error occurs, the error message is stored in the list model, so that it can be shown with the list.

Contributes to issue CURA-8556.

plugins/Marketplace/PackageList.py

@@ -1,10 +1,13 @@
 # Copyright (c) 2021 Ultimaker B.V.
 # Cura is released under the terms of the LGPLv3 or higher.
 
+from PyQt5.QtCore import pyqtProperty, pyqtSignal, pyqtSlot, Qt
+from typing import Optional, TYPE_CHECKING
+
 from cura.CuraApplication import CuraApplication
 from cura.UltimakerCloud.UltimakerCloudScope import UltimakerCloudScope  # To make requests to the Ultimaker API with correct authorization.
-from PyQt5.QtCore import pyqtProperty, pyqtSignal, pyqtSlot, Qt
-from typing import List, Optional, TYPE_CHECKING
+from UM.i18n import i18nCatalog
+from UM.Logger import Logger
 from UM.Qt.ListModel import ListModel
 from UM.TaskManagement.HttpRequestManager import HttpRequestManager  # To request the package list from the API.
 from UM.TaskManagement.HttpRequestScope import JsonDecoratorScope  # To request JSON responses from the API.
@@ -16,6 +19,8 @@ if TYPE_CHECKING:
     from PyQt5.QtCore import QObject
     from PyQt5.QtNetwork import QNetworkReply
 
+catalog = i18nCatalog("cura")
+
 class PackageList(ListModel):
     """
     Represents a list of packages to be displayed in the interface.
@@ -34,6 +39,7 @@ class PackageList(ListModel):
         self._is_loading = True
         self._scope = JsonDecoratorScope(UltimakerCloudScope(CuraApplication.getInstance()))
         self._request_url = f"{Marketplace.PACKAGES_URL}?limit={self.ITEMS_PER_PAGE}"
+        self._error_message = ""
 
         self.addRoleName(self.PackageRole, "package")
 
@@ -47,6 +53,7 @@ class PackageList(ListModel):
         When the request is done, the list will get updated with the new package models.
         """
         self.setIsLoading(True)
+        self.setErrorMessage("")  # Clear any previous errors.
 
         http = HttpRequestManager.getInstance()
         http.get(
@@ -83,6 +90,23 @@ class PackageList(ListModel):
         """
         return self._request_url != ""
 
+    def setErrorMessage(self, error_message: str) -> None:
+        if(self._error_message != error_message):
+            self._error_message = error_message
+            self.errorMessageChanged.emit()
+
+    errorMessageChanged = pyqtSignal()
+
+    @pyqtProperty(str, notify = errorMessageChanged, fset = setErrorMessage)
+    def errorMessage(self) -> str:
+        """
+        If an error occurred getting the list of packages, an error message will be held here.
+
+        If no error occurred (yet), this will be an empty string.
+        :return: An error message, if any, or an empty string if everything went okay.
+        """
+        return self._error_message
+
     def _parseResponse(self, reply: "QNetworkReply") -> None:
         """
         Parse the response from the package list API request.
@@ -92,7 +116,9 @@ class PackageList(ListModel):
         """
         response_data = HttpRequestManager.readJSON(reply)
         if "data" not in response_data or "links" not in response_data:
-            return  # TODO: Handle invalid response.
+            Logger.error(f"Could not interpret the server's response. Missing 'data' or 'links' from response data. Keys in response: {response_data.keys()}")
+            self.setErrorMessage(catalog.i18nc("@info:error", "Could not interpret the server's response."))
+            return
 
         for package_data in response_data["data"]:
             package = PackageModel(package_data, parent = self)
@@ -108,4 +134,5 @@ class PackageList(ListModel):
         :param reply: The reply with packages. This will most likely be incomplete and should be ignored.
         :param error: The error status of the request.
         """
-        pass  # TODO: Handle errors.
+        Logger.error(f"Could not reach Marketplace server.")
+        self.setErrorMessage(catalog.i18nc("@info:error", "Could not reach Marketplace."))