UIImageView *imageView = [[UIImageView alloc]initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
//設定透明度
[imageView setAlpha:0.5];
//這個設定圖像尺寸不對的時候會都顯示在上面,但是圖像會變形,UIViewContentModeScaleAspectFit這個設定圖像會保持比例不變全部顯示,但是會有一部分空白還有一種方法,填充這個imageview但是隻有一部分顯示出來
imageView.contentMode = UIViewContentModeScaleToFill;
UIImage*image1 = [UIImage imageNamed:@"img.jpg"];
[imageView setImage:image1];
[self.view addSubview:imageView];