1# HID DDK Development
2
3## When to Use
4
5The HID driver development kit (DDK) is a toolset that helps you develop HID device drivers at the application layer based on the user mode. It provides interfaces for accessing devices from a host, including creating a device, sending events to a device, and destroying a device.
6
7## Available APIs
8
9| Name| Description|
10| -------- | -------- |
11| OH_Hid_CreateDevice(Hid_Device *hidDevice, Hid_EventProperties *hidEventProperties) | Creates a HID device. When the device is no longer needed, use **OH_Hid_DestroyDevice** to destroy it.|
12| OH_Hid_EmitEvent(int32_t deviceId, const Hid_EmitItem items[], uint16_t length) | Sends events to a HID device.|
13| OH_Hid_DestroyDevice(int32_t deviceId) | Destroys a HID device.|
14
15For details about the APIs, see [HID DDK](../reference/apis-driverdevelopment-kit/_hid_ddk.md).
16
17## How to Develop
18
19The following steps you through the development of a HID device driver with the HID DDK.
20
21**Adding the Dynamic Link Library**
22
23Add the following library to **CMakeLists.txt**.
24```txt
25libhid.z.so
26```
27
28**Including Header Files**
29```c++
30#include <hid/hid_ddk_api.h>
31#include <hid/hid_ddk_types.h>
32```
33
341. Create a device.<br>Use **OH_Hid_CreateDevice** in **hid_ddk_api.h** to create a HID device. If the operation is successful, **deviceId** (a non-negative number) is returned. If the operation fails, an error code (a negative number) is returned.
35
36    ```c++
37   // Construct HID device properties.
38   std::vector<Hid_DeviceProp> deviceProp = {HID_PROP_DIRECT};
39   std::string deviceName = "keyboard"
40   Hid_Device hidDevice = {
41       .deviceName = deviceName.c_str(), 
42       .vendorId = 0x6006, 
43       .productId = 0x6006, 
44       .version = 1, 
45       .bustype = 3,
46       .properties = deviceProp.data(),
47       .propLength = (uint16_t)deviceProp.size()
48   };
49   // Construct the event properties related to the HID device.
50   std::vector<Hid_EventType> eventType = {HID_EV_ABS, HID_EV_KEY, HID_EV_SYN, HID_EV_MSC};
51   Hid_EventTypeArray eventTypeArray = {.hidEventType = eventType.data(), .length = (uint16_t)eventType.size()};
52   std::vector<Hid_KeyCode> keyCode = {HID_BTN_TOOL_PEN, HID_BTN_TOOL_RUBBER, HID_BTN_TOUCH, HID_BTN_STYLUS, HID_BTN_RIGHT};
53   Hid_KeyCodeArray keyCodeArray = {.hidKeyCode = keyCode.data(), .length = (uint16_t)keyCode.size()};
54   std::vector<Hid_MscEvent> mscEvent = {HID_MSC_SCAN};
55   Hid_MscEventArray mscEventArray = {.hidMscEvent = mscEvent.data(), .length = (uint16_t)mscEvent.size()};
56   std::vector<Hid_AbsAxes> absAxes = {HID_ABS_X, HID_ABS_Y, HID_ABS_PRESSURE};
57   Hid_AbsAxesArray absAxesArray = {.hidAbsAxes = absAxes.data(), .length = (uint16_t)absAxes.size()};
58   Hid_EventProperties hidEventProp = {
59       .hidEventTypes = eventTypeArray,
60       .hidKeys = keyCodeArray,
61       .hidAbs = absAxesArray,
62       .hidMiscellaneous = mscEventArray
63    };
64    // Create a device. The device ID of the device created is returned.
65    int32_t deviceId = OH_Hid_CreateDevice(&hidDevice, &hidEventProp);
66    ```
67
682. Send an event to a HID device.<br>Use **OH_Hid_EmitEvent** of **hid_ddk_api.h** to send an event to the device with the specified **deviceId**.
69
70    ```c++
71    // Construct the event to be sent.
72    Hid_EmitItem event = {.type = HID_EV_MSC, .code = HID_MSC_SCAN, .value = 0x000d0042};
73    std::vector<Hid_EmitItem> itemVec;
74    itemVec.push_back(event);
75    // Send the event to a HID device.
76    int32_t ret = OH_Hid_EmitEvent(deviceId, itemVec.data(), (uint16_t)itemVec.size());
77    ```
78
793. Release resources.<br>Use **OH_Hid_DestroyDevice** of **hid_ddk_api.h** to destroy the device after all requests are processed and before the application exits.
80
81    ```c++
82    // Destroy a HID device.
83    int32_t ret = OH_Hid_DestroyDevice(deviceId);
84    ```
85