尝试访问阵列时不断出现访问冲突 [英] Keep getting access violation when trying to access array

问题描述

我对delphi很陌生，当我尝试访问数组"nieuwButtons"时，我一直遇到访问冲突.有人知道我在做什么错吗?

I'm rather new to delp and I keep getting access violations when I try to access my array "nieuwButtons". Does anyone have any idea what I'm doing wrong?

unit UGeneral;

  interface

  uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants,
    System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.Grids, Vcl.DBGrids, SMDBGrid,
    KJSMDBGrid, Vcl.ExtCtrls, KJPanel, Vcl.StdCtrls, Vcl.Mask, Vcl.DBCtrls,
    Data.DB;

  type
    TGeneral = class(TObject)

    private
      { Private declarations }

    public
      nieuwButtons: array of TButton;
      nieuwButtonsDataSource: array of TDataSource;

      procedure listEdits(x, y: Integer; owner: TComponent; parent: TWinControl;
        source: TDataSource);
      procedure nieuwClick(Sender: TObject);
      { Public declarations }
    end;

  var
    General: TGeneral;

  implementation

  procedure TGeneral.nieuwClick(Sender: TObject);
  var
    i: Integer;

  begin
    for i := 0 to Length(nieuwButtons) - 1 do
    begin
      if (nieuwButtons[i] = Sender) then
      begin
        nieuwButtonsDataSource[i].DataSet.Insert;
      end;
    end;
  end;

  procedure TGeneral.listEdits(x, y: Integer; owner: TComponent;
    parent: TWinControl; source: TDataSource);
  var
    i: Integer;
    edit: TDBEdit;
    _label: TLabel;
    biggestWidth: Integer;
    button: TButton;
    edits: array of TDBEdit;
    index: Integer;
  begin
    if nieuwButtons <> nil then //I get an access violation here
    begin
      SetLength(General.nieuwButtons, 0);
      SetLength(nieuwButtonsDataSource, 0);
    end;
    index := Length(nieuwButtons);
    SetLength(nieuwButtons, index + 1);
    SetLength(nieuwButtonsDataSource, index + 1);
    button := TButton.Create(owner);
    button.parent := parent;
    button.Top := y;
    button.Left := x;
    button.Caption := 'Nieuw';
    button.OnClick := nieuwClick;

    nieuwButtons[index] := button;
    nieuwButtonsDataSource[index] := source;

    biggestWidth := 0;
    SetLength(edits, source.DataSet.Fields.Count);
    edit := TDBEdit.Create(owner);
    for i := 0 to source.DataSet.Fields.Count - 1 do
    begin
      _label := TLabel.Create(owner);
      _label.parent := parent;
      _label.Caption := source.DataSet.Fields[i].FieldName;
      _label.Top := ((i * 22) + 30 + y); // 22 = standaard(?) hoogte van edittext
      _label.Left := x;

      _label.Show;

      if _label.Width > biggestWidth then
      begin
        biggestWidth := _label.Width;
      end;
    end;
    i := 0;
    for i := 0 to source.DataSet.Fields.Count - 1 do
    begin
      edit := TDBEdit.Create(owner);
      edit.parent := parent;
      edit.DataField := source.DataSet.Fields[i].FieldName;
      edit.DataSource := source;
      edit.Top := ((i * edit.Height) + 30 + y);
      edit.Left := biggestWidth + 30;
      edits[i] := edit;
      edit.Show;
    end;

  end;

end.

推荐答案

该行代码引发异常的唯一方法是 TGeneral 的实例无效.

The only way for that line of code to raise an exception is if the instance of TGeneral is not valid.

该错误将在实例化该类的代码中找到.此错误的常见形式是:

The error will be found in the code that instantiates the class. Common forms of this error are:

1. 完全忘记实例化对象.
2. 通过在未初始化的实例而非类型上调用构造函数来错误地实例化对象.

为说明后面的错误，它看起来像这样:

To illustrate the latter fault, it looks like this:

var
  General: TGeneral;
....
General.Create; // sometimes this way
General := General.Create; // or sometimes this way

但是正确的方法是这样的:

But the correct way is like this:

General := TGeneral.Create;

这篇关于尝试访问阵列时不断出现访问冲突的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！