Application.DoEvents メソッドとは何？わかりやすく解説 Weblio辞書

注意
このメソッドを呼び出すと、メッセージがイベントを発生させた場合に、コードへの再入力が発生する可能性があります。

使用例

DoEvents メソッドを使用するコード例を次に示します。このコードを実行すると、ユーザーは OpenFileDialog からグラフィックスファイルを選択できます。選択したファイルはフォームに表示されます。DoEvents メソッドの働きにより、フォームは開かれるグラフィックスファイルごとに再描画されます。この例を実行するには、PictureBox1 という名前の PictureBox、OpenFileDialog1 という名前の OpenFileDialog、および fileButton という名前のボタンが配置されているフォームに次のコードを貼り付けます。次に、フォームのコンストラクタまたは Load メソッドから、InitializePictureBox メソッドと InitializeOpenFileDialog メソッドを呼び出します。またこの例では、Button コントロールの Control.Click イベントおよび OpenFileDialog の FileOk イベントが、この例で定義されているイベントハンドラに関連付けられている必要があります。このコードの実行を開始したら、ボタンをクリックしてダイアログボックスを表示します。

Visual Basic

Private Sub InitializePictureBox()
    Me.PictureBox1 = New System.Windows.Forms.PictureBox
    Me.PictureBox1.BorderStyle = _
        System.Windows.Forms.BorderStyle.FixedSingle
    Me.PictureBox1.SizeMode = PictureBoxSizeMode.StretchImage
    Me.PictureBox1.Location = New System.Drawing.Point(72,
 112)
    Me.PictureBox1.Name = "PictureBox1"
    Me.PictureBox1.Size = New System.Drawing.Size(160,
 136)
    Me.PictureBox1.TabStop = False
End Sub

Private Sub InitializeOpenFileDialog()
    Me.OpenFileDialog1 = New System.Windows.Forms.OpenFileDialog

    ' Set the file dialog to filter for graphics files.
    Me.OpenFileDialog1.Filter = _
    "Images (*.BMP;*.JPG;*.GIF)|*.BMP;*.JPG;*.GIF|All files (*.*)|*.*"

    ' Allow the user to select multiple images.
    Me.OpenFileDialog1.Multiselect = True
    Me.OpenFileDialog1.Title = "My Image Browser"
End Sub

Private Sub fileButton_Click(ByVal
 sender As System.Object, _
    ByVal e As System.EventArgs) Handles
 FileButton.Click
    OpenFileDialog1.ShowDialog()
End Sub


' This method handles the FileOK event.  It opens each file 
' selected and loads the image from a stream into PictureBox1.
Private Sub OpenFileDialog1_FileOk(ByVal
 sender As Object, _
ByVal e As System.ComponentModel.CancelEventArgs)
 _
 Handles OpenFileDialog1.FileOk

    Me.Activate()
    Dim file, files() As String
    files = OpenFileDialog1.FileNames

    ' Open each file and display the image in PictureBox1.
    ' Call Application.DoEvents to force a repaint after each
    ' file is read.        
    For Each file In files
        Dim fileInfo As System.IO.FileInfo
 = New System.IO.FileInfo(file)
        Dim fileStream As System.IO.FileStream
 = fileInfo.OpenRead()
        PictureBox1.Image = System.Drawing.Image.FromStream(fileStream)
        Application.DoEvents()
        fileStream.Close()

        ' Call Sleep so the picture is briefly displayed, 
        'which will create a slide-show effect.
        System.Threading.Thread.Sleep(2000)
    Next
    PictureBox1.Image = Nothing
End Sub

private void InitializePictureBox()
{
    this.PictureBox1 = new System.Windows.Forms.PictureBox();
    this.PictureBox1.BorderStyle = 
        System.Windows.Forms.BorderStyle.FixedSingle;
    this.PictureBox1.SizeMode = PictureBoxSizeMode.StretchImage;
    this.PictureBox1.Location = new System.Drawing.Point(72,
 112);
    this.PictureBox1.Name = "PictureBox1";
    this.PictureBox1.Size = new System.Drawing.Size(160,
 136);
    this.PictureBox1.TabIndex = 6;
    this.PictureBox1.TabStop = false;
}

private void InitializeOpenFileDialog()
{
    this.OpenFileDialog1 = new System.Windows.Forms.OpenFileDialog();

    // Set the file dialog to filter for graphics files.
    this.OpenFileDialog1.Filter = 
        "Images (*.BMP;*.JPG;*.GIF)|*.BMP;*.JPG;*.GIF|" + 
        "All files (*.*)|*.*";

    // Allow the user to select multiple images.
    this.OpenFileDialog1.Multiselect = true;
    this.OpenFileDialog1.Title = "My Image Browser";
    
}

private void fileButton_Click(System.Object
 sender, System.EventArgs e)
{
    OpenFileDialog1.ShowDialog();
}


// This method handles the FileOK event.  It opens each file 
// selected and loads the image from a stream into PictureBox1.
private void OpenFileDialog1_FileOk(object
 sender, 
    System.ComponentModel.CancelEventArgs e)
{

    this.Activate();
     string[] files = OpenFileDialog1.FileNames;

    // Open each file and display the image in PictureBox1.
    // Call Application.DoEvents to force a repaint after each
    // file is read.        
    foreach (string file in
 files )
    {
        System.IO.FileInfo fileInfo = new System.IO.FileInfo(file);
        System.IO.FileStream fileStream = fileInfo.OpenRead();
        PictureBox1.Image = System.Drawing.Image.FromStream(fileStream);
        Application.DoEvents();
        fileStream.Close();

        // Call Sleep so the picture is briefly displayed, 
        //which will create a slide-show effect.
        System.Threading.Thread.Sleep(2000);
    }
    PictureBox1.Image = null;
}

C++

void InitializePictureBox()
{
   this->PictureBox1 = gcnew System::Windows::Forms::PictureBox;
   this->PictureBox1->BorderStyle =
      System::Windows::Forms::BorderStyle::FixedSingle;
   this->PictureBox1->SizeMode = PictureBoxSizeMode::StretchImage;
   this->PictureBox1->Location = System::Drawing::Point(
 72, 112 );
   this->PictureBox1->Name = "PictureBox1";
   this->PictureBox1->Size = System::Drawing::Size( 160,
 136 );
   this->PictureBox1->TabIndex = 6;
   this->PictureBox1->TabStop = false;
}

void InitializeOpenFileDialog()
{
   this->OpenFileDialog1 = gcnew System::Windows::Forms::OpenFileDialog;
   
   // Set the file dialog to filter for graphics files.
   this->OpenFileDialog1->Filter =
      "Images (*.BMP;*.JPG;*.GIF)|*.BMP;*.JPG;*.GIF|" +
      "All files (*.*)|*.*";
   
   // Allow the user to select multiple images.
   this->OpenFileDialog1->Multiselect = true;
   this->OpenFileDialog1->Title = "My Image Browser";
}

void fileButton_Click( System::Object^ sender, System::EventArgs^
 e )
{
   OpenFileDialog1->ShowDialog();
}

// This method handles the FileOK event.  It opens each file 
// selected and loads the image from a stream into PictureBox1.
void OpenFileDialog1_FileOk( Object^ sender,
   System::ComponentModel::CancelEventArgs^ e )
{
   this->Activate();
   array<String^>^ files = OpenFileDialog1->FileNames;
   
   // Open each file and display the image in PictureBox1.
   // Call Application.DoEvents to force a repaint after each
   // file is read.        
   for each ( String^ file in files )
   {
      System::IO::FileInfo^ fileInfo = gcnew System::IO::FileInfo( file );
      System::IO::FileStream^ fileStream = fileInfo->OpenRead();
      PictureBox1->Image = System::Drawing::Image::FromStream( fileStream );
      Application::DoEvents();
      fileStream->Close();
      
      // Call Sleep so the picture is briefly displayed, 
      //which will create a slide-show effect.
      System::Threading::Thread::Sleep( 2000 );
   }
   PictureBox1->Image = nullptr;
}

private void InitializePictureBox()
{
    this.pictureBox1 = new System.Windows.Forms.PictureBox();
    this.pictureBox1.set_BorderStyle(
        System.Windows.Forms.BorderStyle.FixedSingle);
    this.pictureBox1.set_SizeMode(PictureBoxSizeMode.StretchImage);
    this.pictureBox1.set_Location(new System.Drawing.Point(72,
 112));
    this.pictureBox1.set_Name("pictureBox1");
    this.pictureBox1.set_Size(new System.Drawing.Size(160,
 136));
    this.pictureBox1.set_TabIndex(6);
    this.pictureBox1.set_TabStop(false);
} //InitializePictureBox

private void InitializeOpenFileDialog()
{
    this.openFileDialog1 = new System.Windows.Forms.OpenFileDialog();
    // Set the file dialog to filter for graphics files.
    this.openFileDialog1.set_Filter("Images (*.BMP;*.JPG;*.GIF)|"
 
        + "*.BMP;*.JPG;*.GIF|All files (*.*)|*.*");
    // Allow the user to select multiple images.
    this.openFileDialog1.set_Multiselect(true);
    this.openFileDialog1.set_Title("My Image Browser");
} //InitializeOpenFileDialog

private void fileButton_Click(Object sender,
 System.EventArgs e)
{
    openFileDialog1.ShowDialog();
} //fileButton_Click

// This method handles the FileOK event. It opens each file 
// selected and loads the image from a stream into pictureBox1.
private void openFileDialog1_FileOk(Object
 sender, 
    System.ComponentModel.CancelEventArgs e)
{
    this.Activate();
    String files[] = openFileDialog1.get_FileNames();
    // Open each file and display the image in pictureBox1.
    // Call Application.DoEvents to force a repaint after each
    // file is read.
    for (int iCtr = 0; iCtr < files.length;
 iCtr++) {
        String file = files[iCtr];
        System.IO.FileInfo fileInfo = new System.IO.FileInfo(file);
        System.IO.FileStream fileStream = fileInfo.OpenRead();
        pictureBox1.set_Image(System.Drawing.Image.FromStream(fileStream));
        Application.DoEvents();
        fileStream.Close();
        // Call Sleep so the picture is briefly displayed, 
        // which will create a slide-show effect.
        System.Threading.Thread.Sleep(2000);
    }
    pictureBox1.set_Image(null);
} //openFileDialog1_FileOk