在UITableView中显示可下载内容的正确方式(使用ProgressBar等)
在UITableView中显示可下载内容的正确方式(使用ProgressBar等)
提问于 2012-08-31 08:04:58
我认为这是一个相当复杂的问题。我有一个TableView，可以显示许多可下载的内容。当你点击单元格中的一个按钮，下载就开始了。
但我遇到了几个问题:1.如何确保progressBar始终显示(即使用户滚动滚动，单元格将被重新加载)2.如何确保用户可以同时下载2个文件。我担心这会导致问题，因为我使用了一些实例变量。在某种程度上，它的工作方式应该有点像在音乐应用程序中从iCloud下载
以下是我的代码
- (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];
}如果有人有线索或很好的代码示例就更好了
回答 2
Stack Overflow用户
回答已采纳
发布于 2012-08-31 13:17:43
重要的是要认识到，进度条不会一直显示(例如，用户可以滚动表格，一旦离开屏幕，相同的单元格就可以在不同内容的另一个索引位置重用)。因此，您需要做的是在某个地方存储有关任何活动下载的数据，包括表中的索引位置、总文件大小和到目前为止下载的字节数。然后，无论何时绘制单元格，都需要检查当前是否正在下载该单元格的项目，如果是，则显示带有适当百分比进度的条形图。
要做到这一点，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NSMutableDictionary对象集合的NSMutablerray，每个字典都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];
}无论何时按下按钮，都会向数组中添加一个包含所需信息的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，我们还将创建两个实用程序方法，以便使用connection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，使用预期长度更新您的字典。
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
// ...
NSDictionary *dict = [self getConnectionInfo:connection];
[dict setObject:[NSNumber numberWithInt:response.expectedContentLength] forKey:@"totalFileSize"];
}在接收数据时，您将更新接收到的字节数，并告诉tableView重新绘制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];
}当您的连接下载完成后，您应该从activeConnections数组中删除该连接，并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];
}
}Stack Overflow用户
发布于 2012-08-31 08:47:47
你的问题是你混淆了你的数据和UI。您依赖于每个表视图单元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，该对象可以存储单元格所需的数据(例如，指示是否正在下载、当前下载进度、下载的数据等的布尔值)。然后，您应该拥有这些对象的可变数组，这样objectAtIndex:0就是表中第一个单元格的数据，依此类推。
当下载开始时，更新数组中的相关对象。理想情况下，当您创建表格视图单元格时，您应该使用NSKeyValueObserving protocol，以便在底层数据发生更改时自动通知它们，并可以适当地更新它们的数据。当一个单元格被重用时，这是很好的，因为存储它的数据的对象仍然在那里，如果因为它即将回到屏幕上而需要再次创建它，那么它将能够使用这些数据来正确地显示。
如果你需要进一步的解释，请告诉我。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/12207288
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