在UITableView中显示可下载内容的正确方法(使用ProgressBar等)

Question

我认为这是一个相当复杂的问题.我有一个显示许多可下载内容的TableView.当您在单元格中的按钮上单击它时,下载开始.

但我有几个问题:1.如何确保progressBar将一直显示(即使用户滚动滚动并重新加载单元格)2.如何确保用户可以下载一次2个文件.我担心它会导致问题,因为我使用了一些实例Variables.在某种程度上它应该有点像在音乐应用程序中从iCloud下载

这是我的代码

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleValue1 reuseIdentifier:nil];   
    }
    //cell.tag = indexPath.row*10;
    Uebungsblaetter *uebungCell = [uebungsblattArray objectAtIndex:indexPath.row];
    cell.tag = indexPath.row*10;
    cell.textLabel.text = [self getFileNameOutOf:uebungCell.url];
    cell.textLabel.textColor = [UIColor grayColor];
    cell.selectionStyle = UITableViewCellSelectionStyleNone;
    UIButton *dl = [UIButton buttonWithType:UIButtonTypeCustom];
    dl.tag = indexPath.row*10;
    [dl setBackgroundImage:[UIImage imageNamed:@"downloadButton.png"] forState:UIControlStateNormal];
    [dl setBackgroundImage:[UIImage imageNamed:@"downloadButtonH.png"] forState:UIControlStateHighlighted];
    [dl setFrame:CGRectMake(230.0, (cell.frame.size.height-28)/2, 28, 28)];
    [dl addTarget:self action:@selector(downloadFileWhenPressedButton:) forControlEvents:UIControlEventTouchUpInside];
    [cell.contentView addSubview:dl];
    UIProgressView *dlProgress = [[UIProgressView alloc] initWithProgressViewStyle:UIProgressViewStyleDefault];
    dlProgress.frame = CGRectMake(cell.frame.size.width-150, 17, 50, 9);
    dlProgress.tag =indexPath.row*10+1;
    dlProgress.progress = 0.0;
    [cell.contentView addSubview:dlProgress];
    [dlProgress setHidden:YES];   

    return cell;
}

//download methods
- (void)downloadFileWhenPressedButton:(UIButton*)sender{
    sender.hidden = YES;
    dlIndex = sender.tag/10;
    Uebungsblaetter *selectedUB = [uebungsblattArray objectAtIndex:dlIndex];
    NSURL *theUrl = [NSURL URLWithString:selectedUB.url];
    NSURLRequest *req=[NSURLRequest requestWithURL:theUrl cachePolicy:NSURLCacheStorageNotAllowed timeoutInterval:120];
    dlCell = (UITableViewCell *)[[sender superview]superview];
    currDlProgress = (UIProgressView* )[dlCell.contentView viewWithTag:dlIndex*10+1];
    currDlProgress.hidden = NO;
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    dlFilePath = [NSString stringWithFormat:@"%@/%@_%@", [paths objectAtIndex:0],self.courseLable.text,[self getFileNameOutOf:selectedUB.url]];
    NSURLConnection *con=[[NSURLConnection alloc] initWithRequest:req delegate:self startImmediately:YES];
    if (con) {
        myWebData = [NSMutableData data];
    }

}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{
    UIApplication* app = [UIApplication sharedApplication];
    app.networkActivityIndicatorVisible = YES;
    currDlProgress.progress = 0;
    _totalFileSize = response.expectedContentLength;
    NSLog(@"%@",@"connection established");
    [myWebData setLength: 0];



}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    _receivedDataBytes += [data length];
    currDlProgress.progress = _receivedDataBytes / (float)_totalFileSize;

    NSLog(@"%@",@"connection receiving data");
    [myWebData appendData:data];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    NSLog(@"%@",@"connection failed");
    //  [AlertViewHandler showAlertWithErrorMessage:@"Sorry, there is no network connection. Please check your network and try again."];
    //  [self parserDidEndDocument:nil];
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    UIApplication* app = [UIApplication sharedApplication];
    app.networkActivityIndicatorVisible = NO;
    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:0.35];
    [currDlProgress setAlpha:0];
    [UIView commitAnimations];
    [myWebData writeToFile:dlFilePath atomically:YES];
    Uebungsblaetter *loadedUB = [uebungsblattArray objectAtIndex:dlIndex];
    loadedUB.downloaded = [NSNumber numberWithBool:YES];
    [courseTable reloadData];
}

如果有人有线索或一个很好的代码示例,那将会很好

Answer 1

重要的是要意识到你的进度条不会一直显示(即用户可以滚动表格,一旦屏幕外,相同的单元格可以在不同内容的另一个索引位置重复使用).因此,您需要做的就是可以存储有关任何活动下载的数据,包括表中的索引位置,总文件大小以及到目前为止下载的字节数.然后,无论何时绘制单元格,您都需要检查当前是否正在下载该单元格的项目,如果是,则显示具有适当百分比进度的条形图.

最简单的方法是向视图控制器添加一个属性来存储此信息.它可以是一个包含对象NSMutablerray集合的NSMutableDictionary对象,每个字典将包含有关活动下载的必要信息.

@property (nonatomic, strong) NSMutableArray *activeConnections;

首先,您将初始化数组viewDidLoad::

- (void)viewDidLoad
{
    [super viewDidLoad];
    //...

    self.activeConnections = [[NSMutableArray alloc] init];
}

每当按下一个按钮时,您将使用您需要的信息向您的阵列添加NSMutableDictionary对象.

- (void)downloadFileWhenPressedButton:(UIButton*)sender
{
    // ...

    //  then create dictionary
    NSMutableDictionary *dict = [[NSMutableDictionary alloc] init];
    [dict setObject:con forKey:@"connection"];  // save connection so we can reference later
    [dict setObject:[NSNumber numberWithInt:[sender.tag]/10] forKey:@"row"];  // this is the row index from your table
    [dict setObject:[NSNumber numberWithInt:999] forKey:@"totalFileSize"];  // dummy size, we will update when we know more
    [dict setObject:[NSNumber numberWithInt:0] forKey:@"receivedBytes"];

    [self.activeConnections addObject:dict];
}

此外,我们将创建两个实用程序方法,以便我们可以使用连接对象本身或表中的行索引位置轻松地从数组中检索连接信息.

- (NSDictionary*)getConnectionInfo:(NSURLConnection*)connection
{
    for (NSDictionary *dict in self.activeConnections) {
        if ([dict objectForKey:@"connection"] == connection) {
            return dict;
        }
    }
    return nil;
}

- (NSDictionary*)getConnectionInfoForRow:(int)row
{
    for (NSDictionary *dict in self.activeConnections) {
        if ([[dict objectForKey:@"row"] intValue] == row) {
            return dict;
        }
    }
    return nil;
}

建立连接后,使用预期长度更新字典 

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    // ...

    NSDictionary *dict = [self getConnectionInfo:connection];
    [dict setObject:[NSNumber numberWithInt:response.expectedContentLength] forKey:@"totalFileSize"];
}

当您收到数据时,您将更新接收的字节数并告诉tableView重绘包含进度条的单元格.

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    // ...

    NSDictionary *dict = [self getConnectionInfo:connection];
    NSNumber bytes = [data length] + [[dict objectForKey:@"receivedBytes"] intValue];

    [dict setObject:[NSNumber numberWithInt:response.expectedContentLength] forKey:@"receivedBytes"];

    int row = [[dict objectForKey:@"row"] intValue];
    NSIndexPath *indexPath = [NSIndexPathindexPathForRow:row inSection:0];
    [self.tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] 
                          withRowAnimation:UITableViewRowAnimationNone];
}

下载完成连接后,应从activeConnections阵列中删除连接,然后重新加载表格单元格.

- (void)connectionDidFinishLoading:(NSURLConnection *)connection 
{
    // ...

    NSDictionary *dict = [self getConnectionInfo:connection];
    [self.activeConnections removeObject:dict];

    int row = [[dict objectForKey:@"row"] intValue];
    NSIndexPath *indexPath = [NSIndexPathindexPathForRow:row inSection:0];
    [self.tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] 
                          withRowAnimation:UITableViewRowAnimationNone];
}

最后,cellForRowAtIndexPath:您需要根据activeConnections数组中的信息绘制单元格的进度条.

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    // ...

    // remove any previous buttons or progress bars from this cell
    for (UIView *view in [cell.contentView subViews]) {

        if ([view isKindOfClass:[UIProgressView class]] || [view isKindOfClass:[UIButton class]]) {
            [view removeFromSuperView];
        }
    }

    // look for active connecton for this cell
    NSDictionary *dict = [self getConnectionInfoForRow:indexPath.row];

    if (dict) {
        // there is an active download for this cell, show a progress bar

        UIProgressView *dlProgress = [[UIProgressView alloc] initWithProgressViewStyle:UIProgressViewStyleDefault];
        dlProgress.frame = CGRectMake(cell.frame.size.width-150, 17, 50, 9);
        dlProgress.tag = indexPath.row*10+1;
        dlProgress.progress = [[dict objectForKey:@"receivedBytes"] intValue] / [[dict objectForKey:@"totalFileSize"] intValue];

        [cell.contentView addSubview:dlProgress];

    } else {
        // no active download, show the download button

        UIButton *dl = [UIButton buttonWithType:UIButtonTypeCustom];
        dl.tag = indexPath.row*10;
        [dl setBackgroundImage:[UIImage imageNamed:@"downloadButton.png"] forState:UIControlStateNormal];
        [dl setBackgroundImage:[UIImage imageNamed:@"downloadButtonH.png"] forState:UIControlStateHighlighted];
        [dl setFrame:CGRectMake(230.0, (cell.frame.size.height-28)/2, 28, 28)];
        [dl addTarget:self action:@selector(downloadFileWhenPressedButton:) forControlEvents:UIControlEventTouchUpInside];
        [cell.contentView addSubview:dl];
    }
}