Delphi解析JSON

如何解决Delphi解析JSON

我需要读取fuelTanks值。之前的一切都归我所有/实际上还有更多内容，但是我不知道如何阅读fuelTanks字段。

我当前的代码：

procedure TMain.JsonAktStav;
var
  JSonObject: TJSonObject;
  data: TJSONArray;
  JSonValue: TJSonValue;
  //*** bJSon is the TByteStream from the previous procedure ***
  idx: integer;
begin
  JSonObject := TJSonObject.Create;
  JSonValue := JSonObject.ParseJSONValue(bJSON.Bytes,bJSON.Size) as TJSONObject;
  JSonValue := (JSonValue as TJSONObject).Get('response').JSonValue;
  JSonValue := (JSonValue as TJSONObject).Get('data').JSonValue;
    
  data := JSonValue as TJSONArray;
    
  for idx := 0 to data.Size - 1 do
  begin
    if (JSonValue is TJSONArray) then
      vehicleid := ((JSonValue as TJSONArray).Items[idx] as TJSonObject).Get('vehicleid').JSonValue.Value;  
  end;

  JSonObject.Free;
  bJSON.Free;
end;

TIdHTTP将返回JSON响应，如下所示：

{
    "response": {
        "actionName": "getActualStates","code": 200,"data": [
            {
                "vehicleid": 4500,"temperatures": [],"fuelTanks": [
                    {
                        "fuelTankNumber": 1,"status": 247
                    },{
                        "fuelTankNumber": 2,"status": 65
                    }
                ]
            },{
                "vehicleid": 4751,"status": 462
                    },"status": 380
                    }
                ]
            }
        ]
    }
}

我无法阅读"fuelTankNumber"和"status"。

解决方法

fuelTanks是一个对象数组，您已经知道如何访问作为数组和对象的子字段，因此只需要进一步扩展代码以更深入地迭代JSON结构即可，例如：>

procedure TMain.JsonAktStav;
var
  JSonValue: TJSonValue;
  data,fuelTanks: TJSONArray;
  vehicle,fuelTank: TJSonObject;
  idx,idx2: integer;
  vehicleid,fuelTankNumber,status: integer;
begin
  try
    //*** bJSon is the TByteStream from the previous procedure ***
    JSonValue := JSonObject.ParseJSONValue(bJSON.Bytes,bJSON.Size);
    if JSonValue <> nil then
    try
      JSonObject := JSonValue as TJSONObject;

      JSonObject := JSonObject.GetValue<TJSONObject>('response');
      data := JSonObject.GetValue<TJSONArray>('data');

      for idx := 0 to data.Size - 1 do
      begin
        vehicle := data.Items[idx] as TJSONObject;

        vehicleid := vehicle.GetValue<Integer>('vehicleid');

        // use vehicleid as needed...

        fuelTanks := vehicle.GetValue<TJSONArray>('fuelTanks');
        
        for idx2 := 0 to fuelTanks.Size - 1 do
        begin
          fuelTank := fuelTanks.Items[idx2] as TJSONObject;

          fuelTankNumber := fuelTank.GetValue<Integer>('fuelTankNumber');
          status := fuelTank.GetValue<Integer>('status');

          // use fuelTankNumber and status as needed...
        end;
      end;
    finally
      JSonValue.Free;
    end;
  finally
    bJSON.Free;
  end;
end;

,

正如我之前所说，我认为使用JSON的最佳方法是序列化和反序列化。

因此，首先，您必须描述代表json的对象（我已将其制作成单位）：

unit Unit3;

interface
TYPE
TMyDoubleArray = Array OF double;

TMyFuelObject = CLASS(TObject)
  PRIVATE
    FFuelTankNumber:integer;
    FStatus:integer;
    procedure SetFuelTankNumber(const Value: integer);
    procedure SetStatus(const Value: Integer);
  PUBLIC
    property fuelTankNumber:integer read FFuelTankNumber write SetFuelTankNumber;
    property status:Integer read FStatus WRITE SetStatus;
END;

TMyFuelArray = ARRAY OF TMyFuelObject;

TMyAnotherOneInnerObject = CLASS(TObject)
  private
    FVehicleId:Integer;
    FTemperatures:TMyDoubleArray;
    FFuelTanks:TMyFuelArray;
    procedure SetFuelTanks(const Value: TMyFuelArray);
    procedure SetTemperatures(const Value: TMyDoubleArray);
    procedure SetVehicleId(const Value: integer);
  PUBLIC
    property vehicleid:integer read FVehicleId WRITE SetVehicleId;
    property temperatures:TMyDoubleArray read FTemperatures write SetTemperatures; //Is it double?
    property fuelTanks:TMyFuelArray read FFuelTanks write SetFuelTanks;
END;

TMyInnerArray = ARRAY of TMyAnotherOneInnerObject;

TMyInnerObject = CLASS(TObject)
  PRIVATE
    FActionName:String;
    FCode:SmallInt;
    FData:TMyInnerArray;
    procedure SetActionName(const Value: String);
    procedure SetCode(const Value: SmallInt);
    procedure SetData(const Value: TMyInnerArray);
  PUBLIC
    property actionName:String read FActionName write SetActionName;
    PROPERTY code:SmallInt read FCode write SetCode;
    PROPERTY data:TMyInnerArray read FData write SetData;
END;

TMyObject = CLASS(TObject)
  PRIVATE
    FResponse:TMyInnerObject;
    procedure SetResponse(const Value: TMyInnerObject);
  PUBLIC
    PROPERTY response:TMyInnerObject READ FResponse WRITE SetResponse;
END;

implementation

{ TMyObject }

procedure TMyObject.SetResponse(const Value: TMyInnerObject);
begin
  FResponse := Value;
end;

{ TMyInnerObject }

procedure TMyInnerObject.SetActionName(const Value: String);
begin
  FActionName := Value;
end;

procedure TMyInnerObject.SetCode(const Value: SmallInt);
begin
  FCode := Value;
end;

procedure TMyInnerObject.SetData(const Value: TMyInnerArray);
begin
  FData := Value;
end;

{ TMyAnotherOneInnerObject }

procedure TMyAnotherOneInnerObject.SetFuelTanks(const Value: TMyFuelArray);
begin
  FFuelTanks := Value;
end;

procedure TMyAnotherOneInnerObject.SetTemperatures(const Value: TMyDoubleArray);
begin
  FTemperatures := Value;
end;

procedure TMyAnotherOneInnerObject.SetVehicleId(const Value: integer);
begin
  FVehicleId := Value;
end;

{ TMyFuelObject }

procedure TMyFuelObject.SetFuelTankNumber(const Value: integer);
begin
  FFuelTankNumber := Value;
end;

procedure TMyFuelObject.SetStatus(const Value: Integer);
begin
  FStatus := Value;
end;

end.

是的，有很多代码。但是，如果将来尝试使用此信息，则比解析json中的每个字段都容易。

然后您必须解析它。我已经将您的JSON放入表单的Memo并实现了此OnButtonClick事件：

uses ... REST.Json,Unit3;

...

procedure TForm2.Button1Click(Sender: TObject);
var json:string;
    myObject:TMyObject;
begin
  json := Memo1.Text;
  try 
     myObject := TJson.JsonToObject<TMyObject>(json);
     //do with myObject everything you want
  finally
     FreeAndNil(myObject);
  end;
end;

然后我得到了：

要获取值，请尝试以下代码：

if length(myObject.response.data) > 0 then
 for i := 0 to length(myObject.response.data) - 1 do
 with myObject.response.data[i] do
   if length(FuelTanks) > 0 then
   for j := 0 to length(FuelTanks) - 1 do
      ShowMessage(FuelTanks[j].FuelTankNumber.ToString); // or inttostr(FuelTanks[j].FuelTankNumber)