用 Vala 解析 JSON
Parse JSON with Vala
我正在尝试解析此 JSON 文档:
{
"registration" : "F-FBZH",
"model" : "DR400-120"
}
这是我做的:
public Plane load_airplane (string registration) {
try {
string? res = null;
var file = File.new_for_path (location + registration + ".json");
if (file.query_exists ()) {
var dis = new DataInputStream (file.read ());
string line;
while ((line = dis.read_line (null)) != null) {
res += line;
}
var parser = new Json.Parser ();
parser.load_from_data (res);
var root_object = parser.get_root ().get_object ();
string data_registration = root_object.get_string_member ("registration");
string data_model = root_object.get_string_member ("model");
return new Plane (data_registration, data_model);
}
} catch (Error e) {
stderr.printf ("%s\n", e.message);
}
return new Plane.default ();
}
它编译没有任何问题,但是当我吃这个程序时我得到了这些错误:
(process:25868): Json-CRITICAL **: json_parser_load_from_data: assertion 'data != NULL' failed
(process:25868): Json-CRITICAL **: json_node_get_object: assertion 'JSON_NODE_IS_VALID (node)' failed
(process:25868): Json-CRITICAL **: json_object_get_string_member: assertion 'object != NULL' failed
(process:25868): Json-CRITICAL **: json_object_get_string_member: assertion 'object != NULL' failed
** (process:25868): CRITICAL **: open_plane_plane_construct: assertion 'registration != NULL' failed
** (process:25868): CRITICAL **: open_plane_plane_get_registration: assertion 'self != NULL' failed
(null)
为什么?另一个问题,为什么用中级语言 Vala 阅读 JSON 这么难?应该会容易很多!
问题是您正在将可为 null 的 res 字符串初始化为 null。
如果您随后向该字符串添加内容,它将保持为空。
string? res = null;
res += "something";
// res will still be null here!
您可以将其初始化为 ""
(空字符串,在这种情况下您也可以只使用不可为 null 的字符串)或者您可以跳过 DataInputStream
并使用 file.load_contents ()
.
我正在尝试解析此 JSON 文档:
{
"registration" : "F-FBZH",
"model" : "DR400-120"
}
这是我做的:
public Plane load_airplane (string registration) {
try {
string? res = null;
var file = File.new_for_path (location + registration + ".json");
if (file.query_exists ()) {
var dis = new DataInputStream (file.read ());
string line;
while ((line = dis.read_line (null)) != null) {
res += line;
}
var parser = new Json.Parser ();
parser.load_from_data (res);
var root_object = parser.get_root ().get_object ();
string data_registration = root_object.get_string_member ("registration");
string data_model = root_object.get_string_member ("model");
return new Plane (data_registration, data_model);
}
} catch (Error e) {
stderr.printf ("%s\n", e.message);
}
return new Plane.default ();
}
它编译没有任何问题,但是当我吃这个程序时我得到了这些错误:
(process:25868): Json-CRITICAL **: json_parser_load_from_data: assertion 'data != NULL' failed
(process:25868): Json-CRITICAL **: json_node_get_object: assertion 'JSON_NODE_IS_VALID (node)' failed
(process:25868): Json-CRITICAL **: json_object_get_string_member: assertion 'object != NULL' failed
(process:25868): Json-CRITICAL **: json_object_get_string_member: assertion 'object != NULL' failed
** (process:25868): CRITICAL **: open_plane_plane_construct: assertion 'registration != NULL' failed
** (process:25868): CRITICAL **: open_plane_plane_get_registration: assertion 'self != NULL' failed
(null)
为什么?另一个问题,为什么用中级语言 Vala 阅读 JSON 这么难?应该会容易很多!
问题是您正在将可为 null 的 res 字符串初始化为 null。
如果您随后向该字符串添加内容,它将保持为空。
string? res = null;
res += "something";
// res will still be null here!
您可以将其初始化为 ""
(空字符串,在这种情况下您也可以只使用不可为 null 的字符串)或者您可以跳过 DataInputStream
并使用 file.load_contents ()
.