UIButton 設置圖片顯示contentmode
只設置contentmode是沒有效果的
UIButton *button;
button.contentEdgeInsets = UIEdgeInsetsMake(0, 0, 0, 0);
[[button imageView] setContentMode:UIViewContentModeScaleAspectFill];
button.contentHorizontalAlignment= UIControlContentHorizontalAlignmentFill;
button.contentVerticalAlignment = UIControlContentVerticalAlignmentFill;