JSON Array From URL in DELPHI

Question

I have the following Json Array from url link.

[{"DATE":"01/10/2021","QUANTITY":4,"UNITPRICE":23.9}, 
 {"DATE":"01/10/2021","QUANTITY":5.85,"UNITPRICE":23.9}, 
 {"DATE":"30/09/2021","QUANTITY":10,"UNITPRICE":23.9}, 
 {"DATE":"04/08/2021","QUANTITY":10,"UNITPRICE":28.83}, 
 {"DATE":"01/07/2021","QUANTITY":1,"UNITPRICE":2.06}, 
 {"DATE":"01/07/2021","QUANTITY":1,"UNITPRICE":2.06}, 
 {"DATE":"30/06/2021","QUANTITY":1,"UNITPRICE":2.06}, 
 {"DATE":"30/06/2021","QUANTITY":1,"UNITPRICE":2.06}]

I want to extract data from the above JSON structure, and later to show it in a Memo or ListView.

Is the proper thing to do to create an Array of Json and put the data in it? When I run my code and click the button, it doesn't show anything. Also, I'm new to Delphi.

Here is the code I have wrote:

function GetURLAsString(const aurl: string): string;
var
  IdHTTP1 : TidHTTP;
begin
  IdHTTP1 := TIdHTTP.Create(nil);
  try
    IdHTTP1.IOHandler := TidSSLIOHandlerSocketOpenSSL.Create(IdHTTP1);
    Result := IdHTTP1.Get(aurl);
  finally
    IdHTTP1.Free;
  end;
end;

procedure TForm4.Button1Click(Sender: TObject);
var
  jso : TJsonObject;
  js : TJsonObject;
  jsv : TJsonValue;
  jsa : TJsonArray;
  jsp : TJsonPair;
  data : string;
  i : integer;
  LItem : TListViewItem;
begin
  try
    data := GetURLAsString('http://....');
  except
    on E: exception do
  end;

  try
    jsv := TJSONObject.ParseJSONValue(data);
    try
      jso := jsv as TJSONObject;
      jsa := TJSONArray.Create();
      jsp := TJSONPair.Create('Array', jsa);
      js.AddPair(jsp);
      jsp := jso.Get('Array');
      jsa := jsp.JsonValue as TJsonArray;
      for I  := 0 to jsa.Size - 1 do
      begin
        jso := jsa.Get(i) as TJsonObject;

        for jsp in jso do
        begin
          if jsp.JsonString.Value  = 'DATE' then
          begin
            form4.ListView1.BeginUpdate;
            LItem := form4.ListView1.Items.Add;
            LItem.Text := jso.GetValue('DATE').ToString;
            form4.ListView1.EndUpdate;
          end;
        end;
      end;
    finally
      jsv.Free;
    end;
  except
    on E: exception do
  end;
end;

You should debug your code. Find our what happens and where it fails. Learning how to debug is one of the first things you need to do as a beginner in order to become productive. — David Heffernan
– David Heffernan, Commented Nov 2, 2021 at 12:20

Kim Madsen · Accepted Answer · 2021-11-02 12:37:37Z

2

I suspect you will get an access violation because you access the method AddPair of the js variable which has not been initialized, and since you catch the exception and igores it, you do not see it.

You are however overcomplicating the solution, which results in bugs. This should work:

jsa := jsv as TJSONArray;
form4.ListView1.BeginUpdate;
try
 for I  := 0 to jsa.Size - 1 do
    begin
       jso := jsa.Get(i) as TJsonObject;
       LItem := form4.ListView1.Items.Add;
       LItem.Text := jso.GetValue('DATE').ToString;
    end;

 finally
  form4.ListView1.EndUpdate;
 end;
finally
  jsv.Free;
end;

answered Nov 2, 2021 at 12:37

Kim Madsen

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