display error events to the user

[r10s]

filing this issue so that it is not forgotten. it's not the most urgent thing to do :)

in general, deltachat-core sends errors to the UI as DC_EVENT_ERROR (there are also DC_EVENT_WARNING and DC_EVENT_INFO, which, however, should not be displayed to the user directly).

the most recent version displays DC_EVENT_ERROR during configuration as a dialog.

however, DC_EVENT_ERROR should also be reported to the user in other situations, possibly in a non-disturbing way.

eg, you will get the DC_EVENT_ERROR event when you're offline and try to send a message. the user should be informed by this, but, as eg. in flaky networks this is quite usual, it would be too much to let the user confirm the error.
(to distinguish between the display methods, for android, we i use a simple flag showErrorAsDialog that is set before configuration and cleared afterwards. if it is set, when handling DC_EVENT_ERROR we save if as a string (as ios does now) else we show a non-disturbing message)

maybe we can use sth. as the "toast" on android for this, here is a very compact example about how this can be implemtented: https://stackoverflow.com/questions/18680891/displaying-a-message-in-ios-which-has-the-same-functionality-as-toast-in-android#answer-49454931

don't know ios, maybe there are also better ways.

maybe it is also an option to just do nothing here - messages that have errors should be flagged anyway and dc_msg_get _info() also gets the error for exactly this message.
maybe this is sufficient and there is nothing more to do :) again, it also depend on what ios users typically expect.

[r10s]

closing this for now, a toast is somewhat unusual on ios.

as an alternative, as mentioned, during configure/import/etc, errors are shown directly. sending errors are visible by the pending-icon.

moreover, the core will add info-messages in these cases.

what's left is, if the server cannot send messages to the device and the internet connection is working meanwhile. showing a toast "cannot receive" one time is not really helping here, i think, sooner or later, the core will provide a function to check this situation, then we can think over how to show this to the user, maybe by just showing "not connected" in the title of the chats-tab. but this is another issue for another time.