Question

我有一个内存缓存，我想写在viewWillDisappear上的文件中，并在viewDidLoad上读回内存。我的代码：

- (void)viewDidLoad
{
    [super viewDidLoad];

    NSFileManager *fileManager = [[NSFileManager alloc] init];
    NSArray *fileArray = [fileManager URLsForDirectory:NSCachesDirectory inDomains:NSUserDomainMask];
    NSString *filePath = [NSString stringWithFormat:@"%@cache_%d", [fileArray lastObject], self.index];
    NSURL *fileUrl = [NSURL URLWithString:filePath];
    if ([fileManager fileExistsAtPath:filePath]) {
        self.thumbnailsCache = [NSDictionary dictionaryWithContentsOfURL:fileUrl];
    }
}

- (void)viewWillDisappear:(BOOL)animated
{
    NSFileManager *fileManager = [[NSFileManager alloc] init];
    NSArray *fileArray = [fileManager URLsForDirectory:NSCachesDirectory inDomains:NSUserDomainMask];
    NSString *filePath = [NSString stringWithFormat:@"%@cache_%d", [fileArray lastObject], self.index];
    NSURL *fileUrl = [NSURL URLWithString:filePath];
    [self.thumbnailsCache writeToURL:fileUrl atomically:YES];
}

基于一些NSLog和调试，它似乎成功写入文件，但在尝试阅读它时只是说找不到文件。我究竟做错了什么？感谢。

修改：self.thumbnailsCache是NSDictionary个NSData个对象。

Answer 1

您错误地创建了filePath。

fileArray是一个URL数组，而不是NSStrings（这是您的代码所假设的）。

因此，如果您将最后一个URL作为要使用的缓存目录，则可以通过以下方式创建缓存文件：

NSURL * cacheURL = (NSURL *)[fileArray lastObject];
if(cacheURL)
{
    NSURL * fileToWrite = [cacheURL URLByAppendingPathComponent: [NSString stringWithFormat:@"%@cache_%d", self.index]];
}

或者，在您的代码的上下文中：

- (void)viewDidLoad
{
    [super viewDidLoad];

    NSFileManager *fileManager = [[NSFileManager alloc] init];
    NSArray *fileArray = [fileManager URLsForDirectory:NSCachesDirectory inDomains:NSUserDomainMask];
    NSString *filePath = [NSString stringWithFormat:@"%@cache_%d", [fileArray lastObject], self.index];

    NSURL * cacheURL = (NSURL *)[fileArray lastObject];
    if(cacheURL)
    {
        NSURL * fileToRead = [cacheURL URLByAppendingPathComponent: [NSString stringWithFormat:@"%@cache_%d", self.index]];
        if(fileToRead && ([fileManager fileExistsAtPath:fileToRead]) {
                self.thumbnailsCache = [NSDictionary dictionaryWithContentsOfURL:fileToRead];
        }
    }
}

- (void)viewWillDisappear:(BOOL)animated
{
    NSFileManager *fileManager = [[NSFileManager alloc] init];
    NSArray *fileArray = [fileManager URLsForDirectory:NSCachesDirectory inDomains:NSUserDomainMask];
    NSString *filePath = [NSString stringWithFormat:@"%@cache_%d", [fileArray lastObject], self.index];

    NSURL * cacheURL = (NSURL *)[fileArray lastObject];
    if(cacheURL)
    {
        NSURL * fileToWrite = [cacheURL URLByAppendingPathComponent: [NSString stringWithFormat: @"%@cache_%d", self.index]];
        if(fileToWrite)
        {
            [self.thumbnailsCache writeToURL:fileToWrite atomically:YES];
        }
    }
}

写入/读取NSData文件失败

1 个答案: