直接用addSubView添加的,
UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
[button setImage:[UIImage imageNamed:@"security-fenceLocation"] forState:UIControlStateNormal];
button.frame = CGRectMake(10.0, CGRectGetMaxY(_mapView.frame) - 90, 35.0, 35.0);
[self addSubview:button];