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。单击单元格内的按钮时，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且单元格将被重新加载） 2.如何确保用户可以一次下载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];
}
如果某人有线索或一个很好的代码示例，那会很好吗
答案 0 :(得分：21)
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。
最简单的方法是在视图控制器中添加一个属性来存储此信息。它可以是NSMutablerray，其中包含NSMutableDictionary个对象的集合，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，您将在viewDidLoad:中初始化数组：
- (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将NSMutableDictionary对象添加到数组中。
- (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，您将更新收到的字节数，并告诉您的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];
}
下载完成后，您应该从activeConnections数组中删除连接，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，在cellForRowAtIndexPath:中，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];
}
}
答案 1 :(得分：3)
您的问题是您正在混淆数据和用户界面。您依靠每个表格视图单元格来存储它的当前下载状态，这将导致问题。相反，您应该创建一个自定义对象，可以存储单元格所需的数据（即bool指示它是否正在下载，当前下载进度，下载的数据等）。然后，您应该拥有这些对象的可变数组，以便objectAtIndex:0是表中第一个单元格的数据，依此类推。
下载开始时，更新阵列中的相关对象。理想情况下，当您创建表格视图单元格时，应使用NSKeyValueObserving protocol，以便在基础数据发生更改时自动通知它们，并可以相应地更新其数据。当一个单元被重用时会很好，因为存储它的数据的对象仍然存在，如果它需要再次制作，因为它即将返回到屏幕上，那么它将能够使用该数据正确显示。
如果您对此任何部分有任何进一步的解释，请与我们联系。