Eggplant with no fruit
When an eggplant has flowers but no fruit, generally this is due to one of two reasons. The first thing that can cause eggplant flowers to fall off is a lack of water and the other is a lack of pollination.
Your eggplant needs at least 2 inches of water a week, more in very hot weather. The majority of that water should be provided in one watering so the water goes deeper into the ground and is less likely to evaporate quickly. Deep watering also encourages the eggplant to grow deep roots, which helps it find water deeper in the ground and even out its water needs so it is less likely to drop a single eggplant flower.
Eggplant flowers contain both pollen producing anthers and pollen receiving pistils, which only take a bit of air movement to move the pollen from one to the other. You can plant a garden that attracts pollinators, increase air circulation or hand transfer pollen. Hand pollinating eggplant is very simple and can be done with your hand by lightly tapping the flower daily during the blooming season from mid to late summer. The goal is to move the pollen from the anther to the pistil. Another way to transfer the pollen to the pistil is to use a delicate brush, like those for fine art or even makeup application. You can also use a soft cotton swab. Gently pick up pollen from inside the flower and move it around. Whichever method you use for pollinating eggplants by hand, the ideal time is in the morning between 6 am and 11 am.
Good luck and happy gardening.