Self-update QAbstractItemDelegate when item changes

[ChrisW67]

Here are the main points:

• The view will not update itself unless the model tells it the data has changed or the user triggers a view change that forces it to refetch the data.
• The model cannot tell the view that underlying data has changed unless it knows itself
• You are changing the underlying data from outside the model and not informing the model.

The usual approach would be, as wysota points out, to put the actual data inside the model and maintain the state of the data through the model instance. You can use the setData() interface to the model, or your own methods, but whenever the model changes the data it must emit the relevant dataChanged() or related signals. When your network reply comes in you insert the new image into the model causing the model to emit dataChanged().

[jiveaxe]

The usual approach would be, as wysota points out, to put the actual data inside the model and maintain the state of the data through the model instance. You can use the setData() interface to the model, or your own methods, but whenever the model changes the data it must emit the relevant dataChanged() or related signals. When your network reply comes in you insert the new image into the model causing the model to emit dataChanged().

I've followed your and wysota way. I subclassed QNetworkAccessManager and now the model calls it with url and index; this new class downloads the image and emits a signal intercepted by the model that in turn emits dataChanged(), as you recommend. Now images are self-updated, as expected. I only encountered a small bug: seems that the model calls the download class 4 times per item and when items are a lot the program crashes with this message:

GLib-ERROR **: Creating pipes for GWakeup: Too many open files

Is there a way to limit model's calls? Or is it best to implement a download manager with queue support?

Thank you both for the valuable help.

[ChrisW67]

The model's data() method will be called multiple times for each model index in the view: for the DisplayRole, DecorationRole, SizeHintRole etc... If you fetch the image once for each call you will indeed be performing efficiency crimes. Make sure you are only fetching a remote image once and storing it in the model for later use.