Question

我需要使用NSURLConnection（GET）知道我正在下载的文件大小（以字节为单位）到我的应用程序中。如果有帮助的话，下面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);
}

Answer 1

[数据长度]会返回以字节为单位的数据大小，它可以为您提供所需的数字。

但NSData提供了-writeToFile：atomically：和-writeToFile：options：将数据写入磁盘的错误方法，所以我不知道你为什么编写自己的文件I / O.

Answer 2

我相信代码来自Apple的SimpleURLConnections示例代码。以下是Apple的NSURLConnection方法“connection：didReceiveData：”

的直接引用

“代表应该连接交付的每个数据对象的内容为a建立完整的数据网址加载。“

NSData没有提供逐步写入文件的方法，它会立即写入所有内容，因此我认为这种以增量方式写入NSOutputStream的方法（此处名为fileStream）是正确的。在此代码中使用dataLength只会在一次调用“connection：didReceiveData：”时返回从NSURLConnection发送到委托的数据的长度，而不是整个连接的数据的总长度。为此，我添加了额外的属性：

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

连接：didReceiveResponse：我使用NSURLResponse方法expectedContentLength来获取整个连接的接收数据文件大小的正确估计值。

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

连接：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);

以下是来自相同SimpleURLConnections代码的打印输出以及我的修改，以显示实际发生的事情：

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，它可能会选择不在“connection：didReceiveData：”的单个调用中一次写入所有数据，因此使用do / while循环来检查这一点。但在此示例中，它将所有数据写入单个do / while迭代中。

此外，您可以使用NSFileHandle，这将始终写入随每个连接发送的整个数据：didReceiveData：call，也是增量。但请注意，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]);
}

如何使用NSURLConnection确定文件下载的大小（以字节为单位）？

2 个答案: