g_dbus_proxy_new_for_bus_sync：断言“g_variant_is_object_path（object_path）”失败

Posted 2023-04-14

【中文标题】g_dbus_proxy_new_for_bus_sync：断言“g_variant_is_object_path（object_path）”失败

【英文标题】：g_dbus_proxy_new_for_bus_sync: assertion 'g_variant_is_object_path (object_path)' failed

【发布时间】：2019-10-08 01:18:16

【问题描述】：

下面的代码应该检索在 DBus 上暴露的 systemd-logind IdleSinceHint 属性

/*
 * Compile with:
 *   gcc -Wall print_user_idle_time.c -o print_user_idle_time `pkg-config --libs gio-2.0 --cflags`
 */

#include <gio/gio.h>

static void
print_user_idle_time (GDBusProxy *proxy)

    gchar *property = "IdleSinceHint";
    GError *error = NULL;
    GVariant *ret;
    guint64 user_idle_time;

    ret = g_dbus_proxy_get_cached_property(proxy, property);
    if (!ret) 
        g_dbus_error_strip_remote_error (error);
        g_print ("IdleSinceHint failed: %s\n", error->message);
        g_error_free (error);
        return;
    

    g_variant_get (ret, "(^ao)", &user_idle_time);
    g_print("%lu\n", user_idle_time);
    g_variant_unref (ret);


int
main (int argc, char *argv[])

    GDBusProxy *proxy;
    gchar *name = "org.freedesktop.login1";
    gchar *object_path = "org/freedesktop/login1";
    gchar *interface_name = "org.freedesktop.login1.Manager";
    /* Create a D-Bus proxy */
    proxy = g_dbus_proxy_new_for_bus_sync (G_BUS_TYPE_SYSTEM,
                                           G_DBUS_PROXY_FLAGS_NONE,
                                           NULL,
                                           name,
                                           object_path,
                                           interface_name,
                                           NULL, NULL);
    g_assert (proxy != NULL);

    print_user_idle_time (proxy);

    g_object_unref (proxy);

    return 0;

但是当它运行时，它在断言 g_assert (proxy != NULL); 上失败并出现错误

(process:9059): GLib-GIO-CRITICAL **: 17:29:07.245: g_dbus_proxy_new_for_bus_sync: assertion 'g_variant_is_object_path (object_path)' failed
**
ERROR:print_user_idle_time.c:44:main: assertion failed: (proxy != NULL)

可能是什么问题？谢谢

【参考方案1】：

您看到的问题是对象路径必须以“/”开头，所以它是/org/freedesktop/login1。

除此之外，属性 GVariant 处理行看起来不合适。这应该足够了：

user_idle_time = g_variant_get_uint64 (ret);

【讨论】：

您的意思是，将g_variant_get (ret, "(^ao)", &user_idle_time); 替换为user_idle_time = g_variant_get_uint64 (ret);？谢谢