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fcl-json/zh CN

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信息

fcl-json 是一个 JSON 的实现.

它包含如下单元:

注: 在 fpjson, 访问形如 SomeJSONObject.Integers['price'] 可能给出一个 SIGSEGV/Access 冲突 如果这个Integer型变量不存在. 这显然是故意的, 看 1. 你必须使用Find方法 (FPC 2.6.2以上可用) 来检查元素 ('price' 在例子中) 是否存在.

流

fcl-json 包含单元“fpjsonrtti”,用于从 JSON 格式加载对象(TObject 实例)或将其保存为 JSON 格式。

简短的示例,请看 Streaming JSON .

例子

入门

pascal
uses
  fpjson, jsonparser;

procedure JSONTest;
var
  jData : TJSONData;
  jObject : TJSONObject;
  jArray : TJSONArray;
  s : String;
begin
  // 这只是使用此 API 可以完成的最小示例

  // 从字符串创建
  jData := GetJSON('{"Fld1" : "Hello", "Fld2" : 42, "Colors" : ["Red", "Green", "Blue"]}');

  // 输出格式化的字符串
  s := jData.AsJSON;

  // 输出格式良好的 JSON
  s := jData.FormatJSON;

  // 转换为 TJSONObject 以使访问更容易
  jObject := jData as TJSONObject;

  // 检索 Fld1 的值
  s := jObject.Get('Fld1');

  // 修改 Fld2 的值
  jObject.Integers['Fld2'] := 123;

  // 检索第二个颜色
  s := jData.FindPath('Colors[1]').AsString;

  // 新增一个元素
  jObject.Add('Happy', True);

  // 新增一个子数组
  jArray := TJSONArray.Create;
  jArray.Add('North');
  jArray.Add('South');
  jArray.Add('East');
  jArray.Add('West');
  jObject.Add('Directions', jArray);

end;

注: 当你使用jData完毕,将它释放时必要的. 否则一个内存泄漏会被制造.

遍历项目

pascal
uses
  Classes, TypInfo, fpjson, jsonparser;

procedure JSONItems(Info: TStrings);
var
  jData : TJSONData;
  jItem : TJSONData;
  i, j: Integer;
  object_name, field_name, field_value, object_type, object_items: String;
begin
  jData := GetJSON('{"A":{"field1":0, "field2": false},"B":{"field1":0, "field2": false}}');

  for i := 0 to jData.Count - 1 do
  begin
    jItem := jData.Items[i];
 
    object_type := GetEnumName(TypeInfo(TJSONtype), Ord(jItem.JSONType));
    object_name := TJSONObject(jData).Names[i];
    WriteStr(object_items, jItem.Count);
 
    Info.Append('object type: ' + object_type + '|object name: ' + object_name + '|number of fields: ' + object_items);
 
    for j := 0 to jItem.Count - 1 do
    begin
      field_name := TJSONObject(jItem).Names[j];
      field_value := jItem.FindPath(TJSONObject(jItem).Names[j]).AsString;
 
      Info.Append(field_name + '|' + field_value);
    end;
  end;
 
  jData.Free;
end;

保存/加载对话框位置/大小

pascal
uses
  jsonConf;

procedure TfmMain.SaveOptionsPos;
var
  c: TJSONConfig;
begin
  c:= TJSONConfig.Create(Nil);
  try
    c.Filename:= GetAppPath(cFileHistory);
    c.SetValue('/dialog/max', WindowState=wsMaximized);
    if WindowState<>wsMaximized then
    begin
      c.SetValue('/dialog/posx', Left);
      c.SetValue('/dialog/posy', Top);
      c.SetValue('/dialog/sizex', Width);
      c.SetValue('/dialog/sizey', Height);
    end;
  finally
    c.Free;
  end;
end;

procedure TfmMain.LoadOptionsPos;
var
  nLeft, nTop, nW, nH: Integer;
  c: TJSONConfig;
begin
  c:= TJSONConfig.Create(Nil);
  try
    c.Filename:= GetAppPath(cFileHistory);

    nLeft:= c.GetValue('/dialog/posx', Left);
    nTop:= c.GetValue('/dialog/posy', Top);
    nW:= c.GetValue('/dialog/sizex', Width);
    nH:= c.GetValue('/dialog/sizey', Height);
    SetBounds(nLeft, nTop, nW, nH);

    if c.GetValue('/dialog/max', false) then
      WindowState:= wsMaximized;
  finally
    c.Free;
  end;
end;

保存/载入 TStringList

pascal
//Example of path: '/list_find'

procedure SLoadStringsFromFile(cfg: TJsonConfig; const path: String; List: TStrings);
var
  i: Integer;
  s: UnicodeString;
begin
  List.Clear;
  for i:= 0 to OptMaxHistoryItems-1 do
  begin
    s:= cfg.GetValue(path+'/'+inttostr(i), '');
    if s='' then
      Break;
    List.Add(Utf8Encode(s));
  end;
end;

procedure SSaveStringsToFile(cfg: TJsonConfig; const path: String; List: TStrings);
var
  i: Integer;
  s: String;
begin
  for i:= 0 to OptMaxHistoryItems-1 do
  begin
    if i<List.Count then
      s:= List[i]
    else
      s:= '';
    cfg.SetDeleteValue(path+'/'+inttostr(i), Utf8Decode(s), '');
  end;
end;

从 JsonViewer

Example usage can be found in the Lazarus jsonviewer tool (located in lazarus/tools/jsonviewer). In particular, this part of the tool shows how to use json:

pascal
procedure TMainForm.OpenFile(Const AFileName : String);
var
  S : TFileStream;
  P : TJSONParser;
  D : TJSONData;
begin
  S:=TFileStream.Create(AFileName,fmOpenRead);
  try
    P:=TJSONParser.Create(S);
    try
      P.Strict:=FStrict;
      D:=P.Parse;
    finally
      P.Free;
    end;
  finally
    S.Free;
  end;
  FFileName:=AFileName;
  SetCaption;
  FreeAndNil(FRoot);
  FRoot:=D;
  ShowJSONDocument;
end;

procedure TMainForm.ShowJSONDocument;
begin
  with TVJSON.Items do
  begin
    BeginUpdate;
    try
      TVJSON.Items.Clear;
      SHowJSONData(Nil,FRoot);
      with TVJSON do
        if (Items.Count>0) and Assigned(Items[0]) then
        begin
          Items[0].Expand(False);
          Selected:=Items[0];
        end;
    finally
      EndUpdate;
    end;
  end;
end;

procedure TMainForm.ShowJSONData(AParent : TTreeNode; Data : TJSONData);
var
  N,N2 : TTreeNode;
  I : Integer;
  D : TJSONData;
  C : String;
  S : TStringList;
begin
  N:=Nil;
  if Assigned(Data) then
  begin
    case Data.JSONType of
      jtArray,
      jtObject:
        begin
          if (Data.JSONType=jtArray) then
            C:=SArray
          else
            C:=SObject;
          N:=TVJSON.Items.AddChild(AParent,Format(C,[Data.Count]));
          S:=TstringList.Create;
          try
            for I:=0 to Data.Count-1 do
              if Data.JSONtype=jtArray then
                S.AddObject(IntToStr(I),Data.items[i])
              else
                S.AddObject(TJSONObject(Data).Names[i],Data.items[i]);
            if FSortObjectMembers and (Data.JSONType=jtObject) then
              S.Sort;
            for I:=0 to S.Count-1 do
            begin
              N2:=TVJSON.Items.AddChild(N,S[i]);
              D:=TJSONData(S.Objects[i]);
              N2.ImageIndex:=ImageTypeMap[D.JSONType];
              N2.SelectedIndex:=ImageTypeMap[D.JSONType];
              ShowJSONData(N2,D);
            end
          finally
            S.Free;
          end;
        end;
      jtNull:
        N:=TVJSON.Items.AddChild(AParent,SNull);
      else
        N:=TVJSON.Items.AddChild(AParent,Data.AsString);
    end;
    if Assigned(N) then
    begin
      N.ImageIndex:=ImageTypeMap[Data.JSONType];
      N.SelectedIndex:=ImageTypeMap[Data.JSONType];
      N.Data:=Data;
    end;
  end;
end;

参考


From the Free Pascal wiki, page "fcl-json/zh CN", as it stood on 2022-05-30 after a change by Iruanp, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's Licensing page. If you have concerns about this material, message the admin.

Revision 1, last changed by WikiArchive .

Edited on wiki.freepascal.org by 1 person, 2022

From the official wiki's backup of 26 May 2024: who edited this page there, and when. Edits made there after that date were not recorded, and the earlier versions are not shown here; the main page says why.

WhenWhoWhat changed
IruanpCreated page
IruanpIruanp moved page fcl-json/zh-CN to fcl-json/zh CN (minor)
Iruanp
Iruanp

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