将 UIActivityIndi​​cator 添加到 UITableView

Question

我需要在表格视图中加载一些数据，当这在后台进行时，我想添加一个活动指示器，以显示有一个进程正在进行，并在进程完成后隐藏。实现这样的事情最有效的方法是什么？

Answer 1

取决于您是否要阻止您的用户，以及活动指示的重要性。

如果您不想阻止用户，请使用Application.networkActivityIndicatorVisible，如果您想要更大的活动指示器但仍不阻止用户，请在表格视图下方使用文本和 UIActivityIndi​​cator 为 UIView 设置动画 (tableview.height -= activityview.height)，然后隐藏完成或如果您想阻止用户，请使用阻止活动指示器。

• http://www.dejal.com/developer/?q=developer/dsactivityview
• https://github.com/jdg/MBProgressHUD（我个人用的是MBProgressHUD，好学好用）

Answer 2

您可以添加一个具有 UIIndicatorView 和 UILabel 的视图作为单元格的子视图。您可以使用这种方式显示错误数据加载/错误网络/空数据...

例子：

您的控制器可以定义两种模式：UITableViewModeMessage 和 UITableViewModeData。

在 viewDidLoad 中，您设置 self.tableViewMode = UITableViewModeMessage。返回数据后，设置 self.tableViewMode = UITableViewModeData 并为 tableview 重新加载数据。

一些代码：

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section 
{
    if (self.tableViewMode == UITableViewModeMessage) {
        return 2;
    } else {
        return self.yourEntries ? self.yourEntries.count : 0;
    }
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{    
    if (self.tableViewMode == UITableViewModeMessage) {
        return [self tableView:tableView messageCellForRowAtIndexPath:indexPath];
    } else {
        return [self tableView:tableView dataCellForRowAtIndexPath:indexPath];
    }
}

- (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath
{
// Remove Loading... progress view if exist.
    UIView *progressView = [cell viewWithTag:100];
    [progressView removeFromSuperview];

    if (self.tableViewMode == UITableViewModeMessage) {        
        if (indexPath.row == 1) {
            // remove the current label.
            cell.textLabel.text = nil;

            // We build progress view and attach to cell here but not in cellForRowAtIndexPath is because in this method cell frame is already calculated.
            UIView *progressView = [self progressViewForCell:cell message:@"Loading..." alpha:0.9];
            [cell addSubview:progressView];
        }
    }
}


// cell to display when loading
- (UITableViewCell *)tableView:(UITableView *)tableView messageCellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"MessageCell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
        cell.textLabel.textColor = [UIColor grayColor];
        cell.textLabel.textAlignment = UITextAlignmentCenter;
    }

    if (indexPath.row == 1) {
        cell.textLabel.text = @"Loading...";
    } else {
        cell.textLabel.text = nil;
    }

    return cell;
}

// cell to display when has data
- (UITableViewCell *)tableView:(UITableView *)tableView dataCellForRowAtIndexPath:(NSIndexPath *)indexPath
{    
    static NSString *CellIdentifier = @"DataCell";

    if (cell == nil) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
    }

    cell.textLabel.text = [[self.yourEntries objectAtIndex:indexPath.row] description];

    return cell;
}

// Build a view which has a UIActivityIndicatorView and a UILabel
- (UIView *)progressViewForCell:(UITableViewCell *)cell message:(NSString *)message alpha:(CGFloat)alpha
{
    // NOTE: progressView needs to be removed from cell in cellForRowAtIndexPath:
    CGRect progressViewFrame = CGRectZero;
    progressViewFrame.size.width = CGRectGetMaxX(cell.bounds);
    progressViewFrame.size.height = CGRectGetMaxY(cell.bounds) - 2;

    UIView *progressView = [[UIView alloc] initWithFrame:progressViewFrame];
    progressView.backgroundColor = RGBA(255, 255, 255, 1);
    progressView.alpha = alpha;
    progressView.tag = 100;

    UILabel *loadingLabel = [[UILabel alloc] initWithFrame:progressView.bounds];
    loadingLabel.backgroundColor = [UIColor clearColor];
    loadingLabel.font = [UIFont systemFontOfSize:14];
    loadingLabel.textColor = [UIColor blackColor];
    loadingLabel.textAlignment = UITextAlignmentCenter;
    loadingLabel.text = message;

    CGFloat widthOfText = [loadingLabel.text sizeWithFont:loadingLabel.font].width;
    CGFloat spaceBetweenIndicatorAndLabel = 5;

    // activityIndicatorView has size in which width and height is equal to 20.
    UIActivityIndicatorView *activityIndicatorView = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
    [activityIndicatorView setCenter:CGPointMake(CGRectGetMidX(cell.bounds) - (widthOfText / 2) - (activityIndicatorView.bounds.size.width / 2) - spaceBetweenIndicatorAndLabel, CGRectGetMidY(cell.bounds))]; 
    [activityIndicatorView setColor:[UIColor blackColor]];
    [activityIndicatorView startAnimating];

    [progressView addSubview:activityIndicatorView];
    [progressView addSubview:loadingLabel];

    return progressView;
}