I assumed that the plants were wild plants as they were growing on a public fence. The fruits must be very useful or even edible for the man to be standing in the hot sun picking them one by one off the vines so a few days later, when I went to visit my friend again, I took some photos of the flower and the fruit. Then I searched the internet for the name of this fruit as my friend did not know what it was and I found the answer.
By looking at the photos below, do you know what fruit this is? It is edible and is sold in supermarkets but its colour is not green when it is ripe and supermarkets usually sell ripe ones only. Please make a guess. Thank you! :)