Actually the clothing are not uniforms per se, but most people in the West think of it that way. The clothing is the typical everyday wear that are worn by many Chinese (and other Asians - the style caught on in other countries) from about 1644 to near WW2.
You don't see it worn much these days because many Asians have adopted western style clothing. However, Asian culture tend to be very traditionally minded so some kept to the style of clothing for special events. Even in most kung fu and tai chi classes, they are not usually worn except for special events such as competitions or exhibitions.
In Ip Man's time, you would see many people on the streets in China wearing this and not just for martial art. In English, it is referred to simply as "Chinese suit" and "Tangzhuang" in Chinese. Sometimes, Tangzhuang and Hanfu are used interchangeably because "Tang" is often confused to mean the Tang Dynasty although the fashion has nothing to do with that period of Chinese history. Hanfu, refers to the more traditional clothing worn during the Tang Dynasty although they use the word "Han". Confused yet?
Asians have a preference for multi-purpose or multi-use items. When Tangzhuang are worn for martial arts, the ends of the legs are usually tied, and the sleeves are rolled back and sometime tied or held back with a button on the upper sleeve. However, during the warmer/hot season, the outer jacket is not worn and only the shirt.