presentViewController 显示半透明效果

在当前controller  present A Controller，透明显示

A*a = [[A alloc]init];

self.definesPresentationContext=YES;

a.view.backgroundColor= [UIColor colorWithRed:0 green:0 blue:0 alpha:0];

catalogViewController.modalPresentationStyle=UIModalPresentationOverCurrentContext;

[selfpresentViewController:catalogViewControlleranimated:YEScompletion:nil];