iOS 设置视图背景的透明度

p.p1 { margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; color: #00afca }
span.s1 { color: #ffffff }
span.s2 { color: #c2349b }
span.s3 { }
span.s4 { color: #8b84cf }

self.backgroundColor = [[UIColor blackColor]colorWithAlphaComponent:0.8f]；