iOS ALAssetsLibrary and NSFileHandle reading file

问题:

I want to read the contents of an assets library file in iOS

NSFileHandle fileHandleForReadingFromUrl using the asset defaultRepresentation url seems to always return 0x0...

I'll keep looking for a solution in the mean time.

EDIT:

Looks like the answer from Anomie might be what I want:

NSUInteger length = [representation getBytes:bytes fromOffset:0 length:[representation size] error:&error];

回答1:

For larger files you probably want to copy out via a loop to read X bytes in chunks, otherwise you are liable to exhaust the on-device memory.

NSUInteger chunkSize = 100 * 1024;
uint8_t *buffer = malloc(chunkSize * sizeof(uint8_t));

ALAssetRepresentation *rep = [myasset defaultRepresentation];
NSUInteger length = [rep size];

NSFileHandle *file = [[NSFileHandle fileHandleForWritingAtPath: tempFile] retain];

if(file == nil) {
    [[NSFileManager defaultManager] createFileAtPath:tempFile contents:nil attributes:nil];
    file = [[NSFileHandle fileHandleForWritingAtPath:tempFile] retain];
}

NSUInteger offset = 0;
do {
    NSUInteger bytesCopied = [rep getBytes:buffer fromOffset:offset length:chunkSize error:nil];
    offset += bytesCopied;
    NSData *data = [[NSData alloc] initWithBytes:buffer length:bytesCopied];
    [file writeData:data];
    [data release];
    } while (offset < length);

[file closeFile];
[file release];
free(buffer);
buffer = NULL;