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我需要知道使用 NSURLConnection (GET) 下载到我的应用程序中的文件的大小（以字节为单位）。如果有帮助，这是我收到的字节代码。我需要知道的是如何以字节为单位获取文件大小，以便我可以使用它来显示 UIProgressView。

- (void)connection:(NSURLConnection *)theConnection didReceiveData:(NSData *)data
// A delegate method called by the NSURLConnection as data arrives.  We just 
// write the data to the file.
{
#pragma unused(theConnection)
    NSInteger       dataLength;
    const uint8_t * dataBytes;
    NSInteger       bytesWritten;
    NSInteger       bytesWrittenSoFar;

    assert(theConnection == self.connection);

    dataLength = [data length];
    dataBytes  = [data bytes];

    bytesWrittenSoFar = 0;
    do {
        bytesWritten = [self.fileStream write:&dataBytes[bytesWrittenSoFar] maxLength:dataLength - bytesWrittenSoFar];
        assert(bytesWritten != 0);
        if (bytesWritten == -1) {
            [self _stopReceiveWithStatus:@"File write error"];
            break;
        } else {
            bytesWrittenSoFar += bytesWritten;

    } while (bytesWrittenSoFar != dataLength);
}
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2 回答 2

2

[数据长度] 确实以字节为单位返回数据的大小，这应该会给你你正在寻找的数字。

但是 NSData 提供了 -writeToFile:atomically: 和 -writeToFile:options:error 方法来将数据写入磁盘，所以我不知道你为什么要编写自己的文件 I/O。

于 2010-02-05T05:18:34.767 回答
1

我相信代码来自 Apple 的 SimpleURLConnections 示例代码。这是来自 Apple 的 NSURLConnection 方法“connection:didReceiveData:”的直接引用

“委托应连接交付的每个数据对象的内容，以构建 URL 加载的完整数据。”

NSData 没有提供增量写入文件的方法，它一次写入所有文件，所以我认为这种增量写入 NSOutputStream 的方法，这里命名为 fileStream，是正确的。在此代码中使用 dataLength 只会返回在一次调用“connection:didReceiveData:”中从 NSURLConnection 发送到委托的数据长度，而不是整个连接的数据总长度。为此，我添加了额外的属性：

@property (nonatomic, assign)   long long dataWrittenForWholeConnection;
@property (nonatomic, assign)   long long dataLengthOfWholeConnection;

在 connection:didReceiveResponse: 我使用了 NSURLResponse 方法 expectedContentLength 来获得对整个连接的接收数据文件大小的正确估计。

self.dataWrittenForWholeConnection = 0;
self.dataLengthOfWholeConnection = [httpResponse expectedContentLength];

在连接中：didReceiveData：我更改了以下内容：

// bytes written for current "connection:didReceiveData:" call
bytesWrittenSoFar += bytesWritten;
// cumulative data written for connection so far
self.dataWrittenForWholeConnection += bytesWritten;

// also update the progress bar
if (self.dataLengthOfWholeConnection != NSURLResponseUnknownLength) {
    self.progressView.progress =
        ((float)self.dataWrittenForWholeConnection / (float)self.dataLengthOfWholeConnection);
}

在连接结束时，这应该是真的：

assert(dataWrittenForWholeConnection == dataLengthOfWholeConnection);

这是来自同一个 SimpleURLConnections 代码的打印输出以及我的修改，以显示实际发生的情况：

connection:didReceiveResponse:
Full size of data is 8789 bytes

connection:didReceiveData:
Data has 1408 bytes
Progress bar is at: 0.160200
1408 bytes of data were written, 1408 bytes so far

connection:didReceiveData:
Data has 1408 bytes
Progress bar is at: 0.320401
1408 bytes of data were written, 2816 bytes so far

connection:didReceiveData:
Data has 1408 bytes
Progress bar is at: 0.480601
1408 bytes of data were written, 4224 bytes so far

connection:didReceiveData:
Data has 1408 bytes
Progress bar is at: 0.640801
1408 bytes of data were written, 5632 bytes so far

connection:didReceiveData:
Data has 1408 bytes
Progress bar is at: 0.801001
1408 bytes of data were written, 7040 bytes so far

connection:didReceiveData:
Data has 1749 bytes
Progress bar is at: 1.000000
1749 bytes of data were written, 8789 bytes so far

connectionDidFinishLoading:
Connection Finished. 8789/8789 bytes of data were written.

此外，NSOutputStream 方法“write:maxLength:”返回“实际写入的字节数”，因此出于某种原因，它可能选择不在一次调用“connection:didReceiveData:”中一次写入所有数据，因此使用 do/while 循环来检查这一点。但在本例中，它在一次 do/while 迭代中写入所有数据。

此外，您可以使用 NSFileHandle 代替，这将始终写入每个连接发送的全部数据：didReceiveData：调用，它也是增量的。但是请注意 writeData: 是同步的。

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    // write data to file handler
    unsigned long long dataLength = [data length];

    NSLog(@"Writing %qu bytes at %qu bytes", dataLength, [self.fileHandle offsetInFile]);
    [self.fileHandle writeData:data];
    NSLog(@"Wrote %qu bytes, now at %qu bytes", dataLength, [self.fileHandle offsetInFile]);
}
于 2011-01-16T01:39:43.573 回答