背景

我正在开发的应用程序旨在让用户创建多媒体项目。其中一个视图显示了当前可用的所有音频文件的列表，还为用户提供了从多个源（包括其音乐库）导入其他文件的选项。

详细

要处理音乐库的导入，我正在使用Chris Adamson在其博客here中发布的代码的变体。用户可以根据需要排队多少导入，代码将自动按顺序导入它们。读/写部分在后台执行，发送通知以让应用程序的其余部分知道进程的状态。

用户可用的所有音频文件都显示在UITableView中。表格视图使用包含标签（显示文件名称）和进度条的自定义单元格（除非歌曲处于导入中间位置，否则始终隐藏）。

以下是单元格的代码：

@interface AudioTableCell()

@property (nonatomic, strong) NSString *importingFileName;

@end


@implementation AudioTableCell


// ---------------------------------------------------------------------------------------------------------------------
- (void) prepareForReuse
{
    // remove notification listeners to avoid creating duplicates
    [[NSNotificationCenter defaultCenter] removeObserver:self name:kNotifMusicLibMgrUpdateProgress object:nil];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:kNotifMusicLibMgrFinishedImportingSong object:nil];

    // reset cell properties to default values
    self.isClickable = YES;
    self.downloadProgress.hidden = YES;
}


// ---------------------------------------------------------------------------------------------------------------------
// called by view controller prior to deleting a cell
- (void) prepareCellForDeletion
{
    [[NSNotificationCenter defaultCenter] removeObserver:self name:kNotifMusicLibMgrUpdateProgress object:nil];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:kNotifMusicLibMgrFinishedImportingSong object:nil];
}


// ---------------------------------------------------------------------------------------------------------------------
// called by the view controller's cellForRowAtIndexPath method
- (void) configureCell
{
    // by default, cell should be clickable and the progress bar should be hidden
    self.isClickable = YES;
    self.downloadProgress.hidden = YES;

    // listen to the import manager for updates on the import's progress
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(importWasUpdated:)
                                                 name:kNotifMusicLibMgrUpdateProgress
                                               object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(importWasFinished:)
                                                 name:kNotifMusicLibMgrFinishedImportingSong
                                               object:nil];

    // when the cell is scrolled out of view, the progress bar is hidden
    // need to remember if depicted song was in process of being downloaded
    if (self.importingFileName.length > 0) {
        if ([self.trackLabel.text isEqualToString:[self.importingFileName stringByAppendingPathExtension:@"m4a"]]) {
            self.downloadProgress.hidden = NO;
            self.isClickable = NO;
        }
    }
}


// ---------------------------------------------------------------------------------------------------------------------
// triggered when receiving a notification that a song has been imported successfully
- (void) importWasFinished:(NSNotification *)notification
{
    // the notification will pass the name of the song that was imported
    NSString *fileName = [notification.userInfo objectForKey:@"audioFileName"];

    // if the song that was imported matches the song being displayed by the cell, hide the progress bar
    // and make the cell clickable
    if ([self.trackLabel.text isEqualToString:[fileName stringByAppendingPathExtension:@"m4a"]]) {
        self.downloadProgress.hidden = YES;
        self.isClickable = YES;
    }

    // if the song that was imported matches the song that was "saved" by the cell, clear the saved song
    if ([self.importingFileName isEqualToString:fileName]) {
        self.importingFileName = @"";
    }
}


// ---------------------------------------------------------------------------------------------------------------------
// triggered when receiving a an update notification (currently 1/second)
- (void) importWasUpdated:(NSNotification *)notification
{
    // the notification will pass the name of the song being imported, its progress, and the number of songs queued
    NSString *fileName = [notification.userInfo objectForKey:@"audioFileName"];
    double completion = [[notification.userInfo objectForKey:@"progress"] doubleValue];

    // if the cell is displaying the song being imported, disable the cell and show a progress bar
    // also, store the name of the song - this way, if the cell is reused for a different song, it will still remember
    // the song being downloaded and can immediately display the progress bar when brought back into view
    if ([self.trackLabel.text isEqualToString:[fileName stringByAppendingPathExtension:@"m4a"]])
    {
        self.isClickable = NO;
        self.downloadProgress.hidden = NO;
        [self.downloadProgress setProgress:completion];
        self.importingFileName = fileName;
    } else {
        self.downloadProgress.hidden = YES;
        self.isClickable = YES;
    }
}


@end

如您所见，单元格侦听来自导入程序的通知，以确定何时隐藏/显示进度条。如果我只尝试导入一首歌曲，则没有重大问题（尽管歌曲完成时间与进度条隐藏的时间之间似乎有一点延迟）。但是，如果我排队多首歌曲，则进度条在完成所有歌曲之前不会消失。更糟糕的是，当单元格被重用时，将单元格滚出视图将导致进度条显示为不同的歌曲。

我已经使用NSLog语句和调试器测试了通知系统，并且它正常工作（“self.downloadProgressBar.hidden = YES;”部分在正确的时间被调用），但进度条仍然可见。在这一点上，我完全没有想法。任何和所有的帮助将不胜感激。

提前致谢。

Answer 1

请检查您的代码是否在主线程上执行。 NSNotification可以在后台线程上发布，因此您的代码将在后台线程上执行，而后台线程不会更新UI。

UITableViewCell没有隐藏进度条

背景

详细

1 个答案: