如何确定 UsbRequest.queue(..) 方法接收的字节长度？
我在 Android 3.1 中遇到 UsbRequest 类的问题。
这是我的代码：
ByteBuffer buffer = ByteBuffer.allocate(4096);
buffer.order(ByteOrder.LITTLE_ENDIAN);
UsbRequest request = new UsbRequest();
request.initialize(mConnection, mEndpointIn);
request.queue(buffer, 4096);
if (mConnection.requestWait() == request) {
byte[] data = buffer.array();
}
数组data的大小是4096，但真正接收到的字节长度要小得多。
如何确定实际接收到的字节大小？
谢谢。
I have troubles with UsbRequest class in Android 3.1.
This is my code:
ByteBuffer buffer = ByteBuffer.allocate(4096);
buffer.order(ByteOrder.LITTLE_ENDIAN);
UsbRequest request = new UsbRequest();
request.initialize(mConnection, mEndpointIn);
request.queue(buffer, 4096);
if (mConnection.requestWait() == request) {
byte[] data = buffer.array();
}
The size of array data is 4096, but the length of really received bytes is much more smaller.
How can i determine the size of really received bytes?
Thanks.
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这是Android 中的一个错误。在受影响的版本上，没有解决方法，因为实现根本不传递长度。
它已在 JB-MR1（API 级别 17 及以上）中修复。
This was a bug in Android. On afflicted versions, there's no workaround, because the implementation simply doesn't pass the length up.
It was fixed in JB-MR1 (API level 17 onwards).
在我看来，当前的异步USB API没有办法返回读取的大小。 2 个“解决方法”使用同步传输，因为您会收到读/写的字节数，或者您正在实现的协议可能会向您发送您将收到的字节数。例如，我目前正在实现一些功能，其中我收到的每个更高级别的数据包在数据包的前 4 个字节中都有字节数。根据这个数字我知道我是否必须进行多次读取。
It seems to me that the current asynchronous USB API has no way to return the read size. 2 "workarounds" use synchronous transfers as there you receive the number of bytes read/written or maybe the protocol you are implementing sends you the number of bytes you'll receive. E.g. i'm currently implementing something where every higher-level packet i receive has the number of bytes in the first 4 bytes of the packet. Based on this number i know if i have to do multiple reads.
您可以使用 request.queue(buffer, bufferLength); 。这应该可以解决你的问题。现在，您应该参考 android 文档，它有详细的文档并且很有帮助。
You can use
request.queue(buffer, bufferLength);. This should solve your problem. Now, you should refer android documentation, it's well documented and helpful.我相信 buffer.limit() 应该返回接收到的字节数。那有用吗？
I believe
buffer.limit()should return the number of received bytes. Does that work?