德尔福 – 从外部关闭模态形式并打开一个新的模态形式

发布时间：2020-12-15 09:23:28 所属栏目：大数据来源：网络整理

导读：在我的主要表单中,我有一个按钮,打开一个模态Form2(可能会打开其他模态形式).在打开Form2之前我正在设置一个计时器,它将以编程方式关闭所有活动的模态表单(Form2.Close)并打开一个新的模态Form3. 问题是当Form3以模态方式打开时,Form2保持(可见)并且只有当我

在我的主要表单中,我有一个按钮,打开一个模态Form2(可能会打开其他模态形式).在打开Form2之前我正在设置一个计时器,它将以编程方式关闭所有活动的模态表单(Form2.Close)并打开一个新的模态Form3.

问题是当Form3以模态方式打开时,Form2保持(可见)并且只有当我通过单击X关闭Form3时才会关闭Form2.

要重现向项目添加3个表单,请添加TButton,并在Form1(主表单)上删除TTimer：

unit Unit1;

interface

uses
  Windows,Messages,SysUtils,Classes,Graphics,Controls,Forms,Dialogs,StdCtrls,ExtCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Timer1: TTimer;
    procedure Button1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure Timer1Timer(Sender: TObject);
  private
  public
  end;

var
  Form1: TForm1;

implementation

uses Unit2,Unit3;

{$R *.DFM}

procedure TForm1.FormCreate(Sender: TObject);
begin
  Timer1.Enabled := False;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  Timer1.Enabled := True;
  with TForm2.Create(Application) do
  try
    ShowModal;
  finally
    Free;
  end;
end;

procedure CloseActiveModalForms;
var
  I: Integer;
  F: TCustomForm;
  L: TList; // list of modal forms
begin
  L := TList.Create;
  try
    for I := 0 to Screen.CustomFormCount - 1 do
    begin
      F := Screen.CustomForms[I];
      if (fsModal in F.FormState) then
        L.Add(F);
    end;
    for I := 0 to L.Count - 1 do
      TCustomForm(L.Items[I]).Close; // this sets ModalResult := mrCancel
  finally
    L.Free;
  end;
end;

procedure TForm1.Timer1Timer(Sender: TObject);
begin
  Timer1.Enabled := False;
  CloseActiveModalForms; // this should close TForm2 but it does not.

  with TForm3.Create(Application) do // create new Modal TForm3
  try
    ShowModal;
  finally
    Free;
  end; 
end;

end.

为什么Form2没有关闭？在调用CloseActiveModalForms后,为什么Form2模态循环不会退出？

解决方法

您的调用堆栈如下所示：

1 Form1.Button1Click
2 Form2.ShowModal //Local message processing loop until form closes
3 Form1.Timer1Timer //Here you attempt to close the form
                    //but it doesn't actually until ShowModal exits
4 Form3.ShowModal // Another message loop that doesn't return until form closes

所以基本上,在Form3关闭之前,你无法完成Form2的关闭.请注意,ShowModal是一个阻止调用来显示表单.如果您只显示Form3(即不是ShowModal),则调用不会阻塞,并且您将看到Form2能够在调用堆栈展开时关闭.

您应该可以通过延迟调用Form3来解决这个问题,直到Form2关闭之后. OnFormDestroyEvent应该足够了(遗憾的是我无法测试它).

procedure TForm1.ShowForm3(Sender: TObject);
var
  LForm: TForm;
begin
  LForm := TForm3.Create(Application); //as you created it,but nil owner should suffice
  try
    LForm.ShowModal;
  finally
    LForm.Free;
  end; 
end;

procedure TForm1.Timer1Timer(Sender: TObject);
begin
  Timer1.Enabled := False;
  //You will need to figure out how you reference the Form2 instance.
  Form2.OnFormDestroy := ShowForm3;
  CloseActiveModalForms;
  //Form2 will close after you backtrack up the call-stack.
  //When it's destroyed,your event handler will create and show a TForm3 instance.
end;

注意上面简单地说明了这个概念.您需要根据您的最终目标设计更强大的方法.

但是,我建议过度使用模态表单通常被认为在用户体验方面不友好.

（编辑：李大同）

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