arrays - 从函数返回动态数组

Question

我正在使用 Delphi 7。

这是我的基类。函数 load_for_edit() 应该返回一个字符串数组，听起来就像这样。问题不是特别在这里，而是更进一步。

    ...

type
    TStringArray = array of string;

    ...

    function load_for_edit(): TStringArray;

    ...

    numberOfFields: integer;

    ...

function TBaseForm.load_for_edit(): TStringArray;
var
    query: TADOQuery;
    i: integer;
begin
    query := TADOQuery.Create(self);
    query.Connection := DataModule1.ADOConnection;
    query.SQL.Add('CALL get_' + self.table_name + '_id(' + self.id + ')');
    query.Open;

    numberOfFields := query.Fields.Count;
    SetLength(result, query.Fields.Count);
    for i := 0 to query.Fields.Count - 1 do
        result[i] := query.Fields[i].Value.AsString;
end;

下一个类是基类的后代，它尝试从基类的 load_for_edit() 函数接收数组。

    ...

type
    TStringArray = array of string;

    ...

procedure TPublisherEditForm.FormShow(Sender: TObject);
var
    rec: TStringArray;
begin
    inherited;
    SetLength(rec, self.numberOfFields);
    rec := load_for_edit();                 // Compilation stops here
end;

但是，应用程序无法编译。 Delphi 吐出此错误消息:

Incompatible types

因此，这意味着函数 load_for_edit() 返回的数据类型与变量 rec 的数据类型不同，如下所示:从它们各自的类型声明部分来看，它们的声明是完全相同的。我不知道这里发生了什么以及该怎么办。请帮我想出一个解决方案。

Answer 1

您有两个单独的 TStringArray 声明(每个单元一个)，并且它们不相同。 (事实上​​，它们位于两个独立的单元中，这使得它们有所不同。UnitA.TStringArray 与 UnitB.TStringArray 不同，即使它们都声明为类型 TStringArray = 字符串数组；。)

您需要使用单一类型声明:

unit
  BaseFormUnit;

interface

uses
  ...
type
  TStringArray: array of string;

  TBaseForm = class(...)
    numberOfFields: Integer;
    function load_for_edit: TStringArray;
  end;

implementation

// Not sure here. It looks like you should use a try..finally to
// free the query after loading, but if you need to use it later
// to save the edits you should create it in the TBaseForm constructor
// and free it in the TBaseForm destructor instead, which means it
// should also be a field of the class declaration above.
function TBaseForm.load_for_edit(): TStringArray;
var
  query: TADOQuery;
  i: integer;
begin
  query := TADOQuery.Create(self);
  query.Connection := DataModule1.ADOConnection;
  query.SQL.Add('CALL get_' + self.table_name + '_id(' + self.id + ')');
  query.Open;

  numberOfFields := query.Fields.Count;
  SetLength(result, numberOfFields);
  for i := 0 to numberOfFields - 1 do
    Result[i] := query.Fields[i].Value.AsString;
end;
...
end.

现在您的后代类可以访问它:

unit
  PublisherEditFormUnit;

interface

uses
  ...  // Usual Forms, Windows, etc.
  BaseFormUnit;

type
  TPublisherEditForm = class(TBaseForm)
  ...
    procedure FormShow(Sender: TObject);
  end;

implementation

procedure TPublisherEditForm.FormShow(Sender: TObject);
var
  rec: TStringArray;
begin
  // No need to call SetLength - the base class does.
  rec := load_for_edit();                 // Compilation stops here
end;
...
end.