UIButton* back = [UIButton buttonWithType:UIButtonTypeCustom];
    [back setImage:[UIImage imageNamed:@"Btn1.png"] forState:UIControlStateNormal];
    back.frame = CGRectMake(0, 0, 40, 40);
    [back setImageEdgeInsets:UIEdgeInsetsMake(0, - 15, 0, 0)]; // 向左边拉伸



    UIBarButtonItem* leftItem = [[UIBarButtonItem alloc] initWithCustomView:back];
    self.navigationItem.leftBarButtonItems = @[leftItem];
    UIButton* right = [UIButton buttonWithType:UIButtonTypeCustom];
    [right setBackgroundColor:[UIColor yellowColor]];
    right.frame = CGRectMake(0, 0, 40, 40);
     [right setImage:[UIImage imageNamed:@"Btn1.png"] forState:UIControlStateNormal];
    [right setImageEdgeInsets:UIEdgeInsetsMake(0, 0, 0, -15)]; // 向右边拉伸

    UIBarButtonItem* rightItem = [[UIBarButtonItem alloc] initWithCustomView:right];
    self.navigationItem.rightBarButtonItem = rightItem;