Android APIs
public class

UsbRequest

extends Object
java.lang.Object
   ↳ android.hardware.usb.UsbRequest

Class Overview

A class representing USB request packet. This can be used for both reading and writing data to or from a UsbDeviceConnection. UsbRequests can be used to transfer data on bulk and interrupt endpoints. Requests on bulk endpoints can be sent synchronously via bulkTransfer(UsbEndpoint, byte[], int, int) or asynchronously via queue(ByteBuffer, int) and requestWait(). Requests on interrupt endpoints are only send and received asynchronously.

Requests on endpoint zero are not supported by this class; use controlTransfer(int, int, int, int, byte[], int, int) for endpoint zero requests instead.

Summary

Public Constructors
UsbRequest()
Public Methods
boolean cancel()
Cancels a pending queue operation.
void close()
Releases all resources related to this request.
Object getClientData()
Returns the client data for the request.
UsbEndpoint getEndpoint()
Returns the endpoint for the request, or null if the request is not opened.
boolean initialize(UsbDeviceConnection connection, UsbEndpoint endpoint)
Initializes the request so it can read or write data on the given endpoint.
boolean queue(ByteBuffer buffer, int length)
Queues the request to send or receive data on its endpoint.
void setClientData(Object data)
Sets the client data for the request.
Protected Methods
void finalize()
Invoked when the garbage collector has detected that this instance is no longer reachable.
[Expand]
Inherited Methods
From class java.lang.Object

Public Constructors

public UsbRequest ()

Added in API level 12

Public Methods

public boolean cancel ()

Added in API level 12

Cancels a pending queue operation.

Returns
boolean true if cancelling succeeded

public void close ()

Added in API level 12

Releases all resources related to this request.

public Object getClientData ()

Added in API level 12

Returns the client data for the request. This can be used in conjunction with setClientData(Object) to associate another object with this request, which can be useful for maintaining state between calls to queue(ByteBuffer, int) and requestWait()

Returns
Object the client data for the request

public UsbEndpoint getEndpoint ()

Added in API level 12

Returns the endpoint for the request, or null if the request is not opened.

Returns
UsbEndpoint the request's endpoint

public boolean initialize (UsbDeviceConnection connection, UsbEndpoint endpoint)

Added in API level 12

Initializes the request so it can read or write data on the given endpoint. Whether the request allows reading or writing depends on the direction of the endpoint.

Parameters
connection UsbDeviceConnection
endpoint UsbEndpoint: the endpoint to be used for this request.
Returns
boolean true if the request was successfully opened.

public boolean queue (ByteBuffer buffer, int length)

Added in API level 12

Queues the request to send or receive data on its endpoint. For OUT endpoints, the given buffer data will be sent on the endpoint. For IN endpoints, the endpoint will attempt to read the given number of bytes into the specified buffer. If the queueing operation is successful, we return true and the result will be returned via requestWait()

Parameters
buffer ByteBuffer: the buffer containing the bytes to write, or location to store the results of a read
length int: number of bytes to read or write
Returns
boolean true if the queueing operation succeeded

public void setClientData (Object data)

Added in API level 12

Sets the client data for the request. This can be used in conjunction with getClientData() to associate another object with this request, which can be useful for maintaining state between calls to queue(ByteBuffer, int) and requestWait()

Parameters
data Object: the client data for the request

Protected Methods

protected void finalize ()

Added in API level 12

Invoked when the garbage collector has detected that this instance is no longer reachable. The default implementation does nothing, but this method can be overridden to free resources.

Note that objects that override finalize are significantly more expensive than objects that don't. Finalizers may be run a long time after the object is no longer reachable, depending on memory pressure, so it's a bad idea to rely on them for cleanup. Note also that finalizers are run on a single VM-wide finalizer thread, so doing blocking work in a finalizer is a bad idea. A finalizer is usually only necessary for a class that has a native peer and needs to call a native method to destroy that peer. Even then, it's better to provide an explicit close method (and implement Closeable), and insist that callers manually dispose of instances. This works well for something like files, but less well for something like a BigInteger where typical calling code would have to deal with lots of temporaries. Unfortunately, code that creates lots of temporaries is the worst kind of code from the point of view of the single finalizer thread.

If you must use finalizers, consider at least providing your own ReferenceQueue and having your own thread process that queue.

Unlike constructors, finalizers are not automatically chained. You are responsible for calling super.finalize() yourself.

Uncaught exceptions thrown by finalizers are ignored and do not terminate the finalizer thread. See Effective Java Item 7, "Avoid finalizers" for more.

Throws
Throwable