Proximity Sensor Usage

The proximity sensor can measure the distance of an object from the front of the device. Some sensors only report the maximum measurement (far) or 0 (near), and they are called wake-up sensors. Before attempting to measure the distance values, you need to know whether the device supports the proximity sensor.

Determining Whether the Sensor Is Supported

To determine whether the proximity sensor is supported on the device:

  1. Create a new project in the Tizen Studio with the Basic UI template, and specify the project name as SensorProximity.

    For more information on how to create a project, see Creating a Project (in mobile and wearable applications).

  2. In the new project, open the sensorproximity.c source file in the src folder and add the required library header file and variables:
    • The sensor.h file is a header file for various sensor libraries.
    • The purpose of the application is to display whether the proximity sensor is supported, and the current distance value. As a result, a variable is defined for both of these values.
    #include "sensorproximity.h"
    #include <sensor.h>
    
    struct appdata {
        Evas_Object *win;
        Evas_Object *conform;
        Evas_Object *label0; /* Whether the proximity sensor is supported */
        Evas_Object *label1; /* Distance value */
    };
    typedef struct appdata appdata_s;
    
  3. Create 2 new functions on top of the create_base_gui() function:
    • The show_is_supported() function identifies whether the proximity sensor is supported, and displays the result in the first label component.

      The sensor_is_supported() function requests the support information. Passing SENSOR_PROXIMITY as the first parameter makes the second parameter return the proximity support information.

    • The my_box_pack() function adds a UI component to a box container.
    static void
    show_is_supported(appdata_s *ad)
    {
        char buf[PATH_MAX];
        bool is_supported = false;
        sensor_is_supported(SENSOR_PROXIMITY, &is_supported);
        sprintf(buf, "Proximity Sensor is %s", is_supported ? "support" : "not support");
        elm_object_text_set(ad->label0, buf);
    }
    
    static void
    my_box_pack(Evas_Object *box, Evas_Object *child,
                double h_weight, double v_weight, double h_align, double v_align)
    {
        /* Tell the child packed into the box to be able to expand */
        evas_object_size_hint_weight_set(child, h_weight, v_weight);
        /* Fill the expanded area (above) as opposed to centering in it */
        evas_object_size_hint_align_set(child, h_align, v_align);
        /* Set the child as the box content and show it */
        evas_object_show(child);
        elm_object_content_set(box, child);
    
        /* Put the child into the box */
        elm_box_pack_end(box, child);
        /* Show the box */
        evas_object_show(box);
    }
    
  4. To create the box, add the 2 labels to the box, and call the show_is_supported() function to determine the sensor support, you must modify the source code at the bottom of the create_base_gui() function as follows:
    /* Conformant */
    /*
       Create and initialize elm_conformant
       elm_conformant is mandatory for the base GUI to have a proper size
       when the indicator or virtual keypad is visible
    */
    ad->conform = elm_conformant_add(ad->win);
    elm_win_indicator_mode_set(ad->win, ELM_WIN_INDICATOR_SHOW);
    elm_win_indicator_opacity_set(ad->win, ELM_WIN_INDICATOR_OPAQUE);
    evas_object_size_hint_weight_set(ad->conform, EVAS_HINT_EXPAND, EVAS_HINT_EXPAND);
    elm_win_resize_object_add(ad->win, ad->conform);
    evas_object_show(ad->conform);
    
    /* Box can contain other elements in a vertical line (by default) */
    Evas_Object *box = elm_box_add(ad->win);
    evas_object_size_hint_weight_set(box, EVAS_HINT_EXPAND, EVAS_HINT_EXPAND);
    evas_object_size_hint_align_set(box, EVAS_HINT_EXPAND, EVAS_HINT_EXPAND);
    elm_object_content_set(ad->conform, box);
    evas_object_show(box);
    
    /* First label (for the sensor support) */
    ad->label0 = elm_label_add(ad->conform);
    elm_object_text_set(ad->label0, "Msg -");
    my_box_pack(box, ad->label0, 1.0, 0.0, -1.0, -1.0);
    
    /* Second label (for the current distance value) */
    ad->label1 = elm_label_add(ad->conform);
    elm_object_text_set(ad->label1, "Value -");
    my_box_pack(box, ad->label1, 1.0, 1.0, -1.0, -1.0);
    
    /* Show the window after the base GUI is set up */
    evas_object_show(ad->win);
    
    /* Check the sensor support */
    show_is_supported(ad);
    
  5. Build (in mobile and wearable applications) and run (in mobile and wearable applications) the application. If the proximity sensor is supported, the Proximity Sensor is support message is shown on the device screen.

    Not all smartphones support this sensor. In that case, test the application on the emulator.

    Proximity Sensor is supported

Requesting Sensor Events

To implement a feature that requests the corresponding event as the proximity sensor detects an object, and displays the distance value on the screen:

  1. Add a structure for the sensor and a global variable to the top of the sensorproximity.c source file:

    • The sensorinfo_s structure includes a sensor handle and an event listener variable.
    • The sensor_info is a global variable of the sensorinfo_s structure.
    struct appdata {
        Evas_Object *win;
        Evas_Object *conform;
        Evas_Object *label0;
        Evas_Object *label1;
    };
    typedef struct appdata appdata_s;
    
    struct _sensor_info {
        sensor_h sensor; /* Sensor handle */
        sensor_listener_h sensor_listener; /* Sensor listener */
    };
    typedef struct _sensor_info sensorinfo_s;
    
    static sensorinfo_s sensor_info;
    
  2. To request sensor events, you need a sensor handle and an event listener, and must start the listener. Create 2 new functions above the create_base_gui() function:
    • The _new_sensor_value() function is an event callback for the proximity sensor, and it outputs a new sensor value to the screen.

      The sensor data is passed to the second parameter. The distance data is saved in values[0].

    • The start_proximity_sensor() function starts the proximity sensor and specifies the event callback function:
      • The sensor_get_default_sensor() function gets a specific sensor handle. Passing SENSOR_PROXIMITY to the first parameter returns an proximity sensor handle to the second parameter.
      • The sensor_create_listener() function creates an event listener. Passing a sensor handle to the first parameter returns a listener object to the second parameter.
      • The sensor_listener_set_event_cb() function specifies a callback function to the listener. The parameters follow this order: event listener, interval (in milliseconds), callback function name, and user data.
      • The sensor_listener_start() function starts the listener.
    static void
    _new_sensor_value(sensor_h sensor, sensor_event_s *sensor_data, void *user_data)
    {
        if (sensor_data->value_count < 1)
            return;
        char buf[PATH_MAX];
        appdata_s *ad = (appdata_s*)user_data;
    
        sprintf(buf, "Distance: %0.1f", sensor_data->values[0]);
        elm_object_text_set(ad->label1, buf);
    }
    
    static void
    start_proximity_sensor(appdata_s *ad)
    {
        sensor_error_e err = SENSOR_ERROR_NONE;
        sensor_get_default_sensor(SENSOR_PROXIMITY, &sensor_info.sensor);
        err = sensor_create_listener(sensor_info.sensor, &sensor_info.sensor_listener);
        sensor_listener_set_event_cb(sensor_info.sensor_listener, 100, _new_sensor_value, ad);
        sensor_listener_start(sensor_info.sensor_listener);
    }
    
  3. To operate the event listener automatically when the application starts running, invoke the above start_proximity_sensor() function at the end of the create_base_gui() function:
    /* Show the window after the base GUI is set up */
    evas_object_show(ad->win);
    
    show_is_supported(ad);
    start_proximity_sensor(ad);
    
  4. Run the application again. To test it on your smartphone, simply bring the device close to your face.

    To test on the emulator, use the control panel:

    1. Right-click the emulator and select Control Panel.
    2. Click Next in the lower-right corner until you see the Proximity box.
    3. Click the box to toggle between Far and Near values. The Near value in the control panel makes the second label component on the application screen show 0.0. If you change the value to Far, the label component displays 5.0.

      Proximity sensor emulator control panel