while he will be doing his homework,i will be playing basket

应该是While he is doing his...
英语中有个语法规则是：时间及条件状语从句用现在时表将来,也就是说在两种从句中不可用将来时.上句while“当...时”,引导时间状语从句.其他例句：
条件状语从句：If it rains tomorrow,we will not go out for a picnic.(不可说成If it will rain...)
时间状语从句：When he finishes his homework,he will be able to play with us.(不可说成When he will...)
希望对你有所帮助：)