Due to the needs of the project, a signature drawing board was developed. The scheme is to use touchesBegan and touchesMoved to record the finger trajectory used for drawing. This is not complicated, so I don't need to go into details. After the function is completed, there is a problem: fingers sliding from the left edge of the screen cannot trigger touches begun, that is, you can't draw lines from the left edge of the screen to the right, but you can draw lines from right to left. After a Google operation, I finally found the reason. It turned out that the sliding gesture of the navigation bar collided with the drawing gesture (it should be that the recognition of the sliding gesture hindered touchesBegan's reaction). Because my signature interface doesn't need to slide backwards, I turned off the back gesture and successfully solved this problem:

The gesture of mentioning 3D Touch on the Internet will also lead to similar problems. After self-testing, my problem is not caused by this reason.

The reference link "Touch Start: Event:" is delayed at the left edge of the screen.

Although the link mentioned 3D Touch, it gave me an idea. If turning off the back gesture doesn't solve your problem, try turning off the 3D Touch gesture.