使用约束给tableview添加暂无数据的提示

在tableview没有数据的时候，我们经常需要在tableview的正中间插入一张图片，来提示用户暂无数据

 

/**
 *  添加一个view，提示暂无数据
 */
- (void)addPromptView
{
    UIView* promptView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, [UIScreen mainScreen].bounds.size.width, 150)];
    UIImageView* promptImageView = [[UIImageView alloc] init];
    CGFloat promptImageViewW = 107;
    CGFloat promptImageViewX = (promptView.frame.size.width - promptImageViewW) / 2;
    CGFloat promptImageViewY = 0;
    CGFloat promptImageViewH = 96;
    CGRect promptF = CGRectMake(promptImageViewX, promptImageViewY, promptImageViewW, promptImageViewH);
    promptImageView.frame = promptF;
    promptImageView.image = [UIImage imageNamed:@"暂无数据.png"];
    promptImageView.contentMode = UIViewContentModeScaleAspectFit;
    promptView.center = self.view.center;
    [promptView addSubview:promptImageView];
    self.promptView = promptView;
    self.promptView.hidden = YES;
    [self.tableView addSubview:self.promptView];
    
//添加约束，使promptView保持在tableview的正中间
    [promptView setTranslatesAutoresizingMaskIntoConstraints:NO];
    [self.tableView addConstraint:[NSLayoutConstraint constraintWithItem:promptView attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.tableView attribute:NSLayoutAttributeCenterX multiplier:1.0f constant:0.0f]];
    [self.tableView addConstraint:[NSLayoutConstraint constraintWithItem:promptView attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.tableView attribute:NSLayoutAttributeCenterY multiplier:1.0f constant:0.0f]];
    [self.tableView addConstraint:[NSLayoutConstraint constraintWithItem:promptView attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:0.0f constant:[UIScreen mainScreen].bounds.size.width]];
    [self.tableView addConstraint:[NSLayoutConstraint constraintWithItem:promptView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:0.0f constant:150.0f]];
    
}