Java/开发/输入/事件X

Question

目前我有一个 N-Trig Multitouch 面板连接到事件文件/dev/input/event4，我正在尝试 this访问它。我已经在 java.library.path 中包含了所有本地人等，但即使是 super 用户，我也会收到此错误。异常:

java.io.IOException: Invalid argument
    at sun.nio.ch.FileDispatcherImpl.read0(Native Method)
    at sun.nio.ch.FileDispatcherImpl.read(FileDispatcherImpl.java:46)
    at sun.nio.ch.IOUtil.readIntoNativeBuffer(IOUtil.java:223)
    at sun.nio.ch.IOUtil.read(IOUtil.java:197)
    at sun.nio.ch.FileChannelImpl.read(FileChannelImpl.java:149)
    at com.dgis.input.evdev.EventDevice.readEvent(EventDevice.java:269)
    at com.dgis.input.evdev.EventDevice.access$1(EventDevice.java:265)
    at com.dgis.input.evdev.EventDevice$1.run(EventDevice.java:200)
EVENT:  null
Exception in thread "Thread-0" java.lang.NullPointerException
    at com.asdev.t3.Bootstrap$1.event(Bootstrap.java:41)
    at com.dgis.input.evdev.EventDevice.distributeEvent(EventDevice.java:256)
    at com.dgis.input.evdev.EventDevice.access$2(EventDevice.java:253)
    at com.dgis.input.evdev.EventDevice$1.run(EventDevice.java:201)

有人知道为什么会这样吗？谢谢

Answer 1

我在项目的 issues page 上回答了这个问题.

by attilapara
Hi, I tried to use this library on a Raspberry Pi and I got the same exception, but I figured out the source of the problem and managed to get it work. Basically, the problem is that this library is written for 64 bit CPU/OS only. Explanation:

The input_event structure looks like this (source):

struct input_event {
    struct timeval time;
    unsigned short type;
    unsigned short code;
    unsigned int value;
};

Here we have timeval, which has the following members (source):

time_t         tv_sec      seconds
suseconds_t    tv_usec     microseconds

These two types are represented differently on a 32 bit and a 64 bit system.

The solution:

1. Change the size of input_event from 24 to 16 bytes:

change line 34 of the source file evdev-java/src/com/dgis/input/evdev/InputEvent.java from this:

    public static final int STRUCT_SIZE_BYTES = 24; to this:

    public static final int STRUCT_SIZE_BYTES = 16; Change the parse function in the same source file as follows:

public static InputEvent parse(ShortBuffer shortBuffer, String source) throws IOException {
    InputEvent e = new InputEvent();
    short a,b,c,d;

    a=shortBuffer.get();
    b=shortBuffer.get();
    //c=shortBuffer.get();
    //d=shortBuffer.get();
    e.time_sec = (b<<16) | a; //(d<<48) | (c<<32) | (b<<16) | a;
    a=shortBuffer.get();
    b=shortBuffer.get();
    //c=shortBuffer.get();
    //d=shortBuffer.get();
    e.time_usec = (b<<16) | a; //(d<<48) | (c<<32) | (b<<16) | a;
    e.type = shortBuffer.get();
    e.code = shortBuffer.get();
    c=shortBuffer.get();
    d=shortBuffer.get();
    e.value = (d<<16) | c;
    e.source = source;

    return e;
}