为TFrame的后代执行了两次加载程序 [英] Loaded procedure executed twice for TFrame's descendant

问题描述

我已经将 TFrame 的后代类注册为组件，并且我注意到 Loaded 过程执行了两次:

I've registered as component a TFrame's descendant class and I've noticed that the Loaded procedure is executed twice:

运行时:

  TMyFrame = class(TFrame)
  private
  protected
    procedure Loaded(); override;
  public
    constructor Create(AOwner : TComponent); override;
  end;

constructor TMyFrame.Create(AOwner : TComponent);
begin
  ShowMessage('Before TMyFrame.Create');
  inherited Create(AOwner);
  ShowMessage('After TMyFrame.Create');
end;

procedure TMyFrame.Loaded();
begin
  ShowMessage('Before TMyFrame.Loaded');
  inherited;
  ShowMessage('After TMyFrame.Loaded');
end;

设计时间:

procedure Register;
begin
  RegisterComponents('Test', [TMyFrame]);
end;

输出:

在运行时，创建包含 TMyFrame 组件的表单时.

At runtime, on creating a form in which there is a TMyFrame component.

在TMyFrame.Create之前

Before TMyFrame.Create

在TMyFrame.Loaded之前

Before TMyFrame.Loaded

TMyFrame.Loaded之后

After TMyFrame.Loaded

在TMyFrame.Create之后

After TMyFrame.Create

在TMyFrame.Loaded之前

Before TMyFrame.Loaded

TMyFrame.Loaded之后

After TMyFrame.Loaded

在设计时，将 TMyFrame 添加到表单中:

At designtime, on adding a TMyFrame to a form:

在TMyFrame.Create之前

Before TMyFrame.Create

在TMyFrame.Loaded之前

Before TMyFrame.Loaded

TMyFrame.Loaded之后

After TMyFrame.Loaded

在TMyFrame.Create之后

After TMyFrame.Create

在设计时，打开一个包含 TMyFrame 组件的表单:

At designtime, opening a form in which there is a TMyFrame component:

在TMyFrame.Create之前

Before TMyFrame.Create

在TMyFrame.Loaded之前

Before TMyFrame.Loaded

TMyFrame.Loaded之后

After TMyFrame.Loaded

在TMyFrame.Create之后

After TMyFrame.Create

在TMyFrame.Loaded之前

Before TMyFrame.Loaded

TMyFrame.Loaded之后

After TMyFrame.Loaded

为什么 Loaded 过程执行两次?如何避免这种情况?

Why the Loaded procedure is executed twice? How to avoid this?

推荐答案

此行为是设计的.

已加载

在继承的表单上可以多次调用Loaded.叫做每次继承级别都流进时.不要分配覆盖的Loaded方法中的内存，而无需先检查在上一次调用中尚未分配内存.

Loaded may be called multiple times on inherited forms. It is called every time a level of inheritance is streamed in. Do not allocate memory in an overridden Loaded method without first checking that the memory has not been allocated in a previous call.

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