I've an object with the filed "hasDownloaded" who is a int.
I need to modify this field without using /manage_propertiesForm ( by code) when someone load this object view, on other word I need to increment the int "hasDownloaded" each time the trialdownload_view is "loaded".
So you have a custom content type called "TrialDownload"
You could create a custom browser view and associated it with the "TrialDownload" content type. It would write to the hasDownloaded field whenever it is called.
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I'm not sure if this is the ideal solution but it should work.
Are you sure you need to do it that way ?
I am thinking: the 'normal file' download is actually a (browser) view. You could maybe override this for your content type and do the counting in the view, and 'save 'the results' from there
I dont think you need a field, especially if there is just one download you want to track.
Just for information: a 'normal' download link should be something like http://site/path/to/file/@@download
Its a view with 2 buttons, they only download the file if they click into the button and I need to count it.