How to sort a TJSONArray in delphi

» json » How to sort a TJSONArray in delphi

By : Zied Saïdi

Date : November 27 2020, 05:23 PM

Does that help I ran into this problem a while back. I didn't find any methods that could do the sorting so ended up building my own:

code :

procedure SortJsonArray(aJsonArray: TJsonArray)
var
  cntr: Integer;
  elementList: TList<TJSONValue>;
begin
  // Sort the elements. We have to sort them because they change constantly
  elementList := TList<TJSONValue>.Create;
  try
    // Get the elements
    for cntr := 0 to aJsonArray.Count - 1 do
      elementList.Add(aJsonArray.Items[cntr]);
    elementList.Sort(TComparer<TJSONValue>.Construct(
        function(const Left, Right: TJSONValue): Integer
        var
          leftObject: TJSONObject;
          rightObject: TJSONObject;
        begin            
          // You should do some error checking here and not just cast blindly
          leftObject := TJSONObject(Left);
          rightObject := TJSONObject(Right);
          // Compare here. I am just comparing the ToStrings but you will probably
          // want to compare something else.
          Result := 
              TComparer<string>.Default.Compare(leftObject.ToString, rightObject.ToString);
        end));
    aJsonArray.SetElements(elementList);
  except
    on E: Exception do
    begin
      // We only free the element list when there is an exception because SetElements 
      // takes ownership of the list.
      elementList.Free;
      raise;
    end;
  end;
end;

Share :

Delphi TJSONArray.ToBytes Access violation - Is it

By : Mary Beel

Date : March 29 2020, 07:55 AM

This might help you Yes, your use of SizeOf() is wrong. iCJSONCallData is an object, so SizeOf(iCJSONCallData) is effectively the same as SizeOf(Pointer), which is 4 on 32bit and 8 on 64bit.
You need to use the TJSONArray.EstimatedByteSize() method instead:

code :

SetLength(vJSONCallDataBytes, iCJSONCallData.EstimatedByteSize);
vCount := iCJSONCallData.ToBytes(vJSONCallDataBytes, 0);

Find Value Type of a JSONValue (TJSONArray or TJSONObject)

By : haaapppy

Date : March 29 2020, 07:55 AM

Does that help I would like to do this with the standard Library in Delphi XE8 , You could use the is operator:

code :

if Assigned(JSONValue) then
begin
  if JSONValue is TJSONArray then
    ProcessArrayResponse(TJSONArray(JSONValue))
  else if JSONValue is TJSONObject then
    ProcessObjectResponse(TJSONObject(JSONValue));
end;

type
  JsonValueType = (jsArray, jsObject, ...);

function GetJsonValueType(JSONValue: TJSONValue): JsonValueType;
begin
  if JSONValue is TJSONArray then Exit(jsArray);
  if JSONValue is TJSONObjct then Exit(jsObject);
  ...
end;

...

if Assigned(JSONValue) then
begin
  case GetJsonValueType(JSONValue) of
    jsArray  : ProcessArrayResponse(TJSONArray(JSONValue));
    jsObject : ProcessObjectResponse(TJSONObject(JSONValue));
  end;
end;

type
  JsonValueType = (jsArray, jsObject, ...);

var
  JsonValueTypes: TDictionary<String, JsonValueType>;

...

if Assigned(JSONValue) then
begin
  case JsonValueTypes[JSONValue.ClassName] of
    jsArray  : ProcessArrayResponse(TJSONArray(JSONValue));
    jsObject : ProcessObjectResponse(TJSONObject(JSONValue));
  end;
end;

...

initialization
  JsonValueTypes := TDictionary<String, JsonValueType>.Create;
  JsonValueTypes.Add('TSONArray', jsArray);
  JsonValueTypes.Add('TSONObject', jsObject);
  ...
finalization
  JsonValueTypes.Free;

Delphi - How do I create a TJSONArray from a array of strings?

By : Colin Lim

Date : March 29 2020, 07:55 AM

I wish this help you You need to construct an empty TJSONArray object first, and then Add() the individual strings values to it. For example:

code :

var
  arr: array of string;
  JSONObj: TJSONObject;
  response_faults: TJSONArray;
  I: Integer;
begin
  arr := ... ; // '001', '002', '005', '009', ...
  JSONObj := TJSONObject.Create;
  try
    response_faults := TJSONArray.Create;
    try
      for I := Low(arr) to High(arr) do begin
        response_faults.Add(arr[I]);
      end;
      JSONObj.AddPair('Events', response_faults);
    except
      response_faults.Free;
      raise;
    end;
    // use JSONObj as needed...
  finally
    JSONObj.Free;
  end;
end;

Update TJSONArray

By : Danny Darwin

Date : March 29 2020, 07:55 AM

help you fix your problem Unfortunately, TJSONArray does not natively allow you to REPLACE existing elements with new values (Why? Who knows). All you can do is ADD and REMOVE elements, and ENUMERATE elements.
Since your array holds TJSONObject instances, to replace such an element with a new object, you will have to either:

Do I need to free instance of TJSONArray

By : esz

Date : March 29 2020, 07:55 AM

With these it helps It depends on which platform you are running on.
If your app is running on a non-ARC platform, such as Windows or OSX, then YES, you need to manually free the TJSONArray when you are done using it, or else it will be leaked.