如何删除已释放的子视图

for (int i = 0; i < 9, i++) {
        UIButton *btn = [indexButtons objectAtIndex:i];
    btn.tag = x;
    [notePage1 addSubview:btn];
    [btn release];

}

UIButton *btn = [indexButtons objectAtIndex:0];
if ([btn isDescendantOfView:notePage1]) { [btn removeFromSuperview]; }
[btn release];

retain

alloc

copy

new

release

for (int i = 0; i < 9, i++) {
        UIButton *btn = [indexButtons objectAtIndex:i];
    btn.tag = x;
    [notePage1 addSubview:btn];
}

UIButton *btn = [indexButtons objectAtIndex:0];
if ([btn isDescendantOfView:notePage1]) { [btn removeFromSuperview]; }