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OnPaint is not called if the form has no focus

I have a custom control with custom painting. The constructor sets the styles correctly from what I can say. Main code:

public partial class LineChart2 : UserControl
{
    public LineChart2()
    {
        InitializeComponent();

        //Set control styles to eliminate flicker on redraw and to redraw on resize
        this.SetStyle(
            ControlStyles.ResizeRedraw |
            ControlStyles.UserPaint |
            ControlStyles.AllPaintingInWmPaint |
            ControlStyles.DoubleBuffer,
            true);

        SetDefaultValues();
    }

    protected override void OnPaint(PaintEventArgs e)
    {
    // breakpoint set here for verification
        Paint~misc stuff(e.Graphics);

        base.OnPaint(e);
    }

    private void UpdateGraph()
    {
    // this is called when the data that the control depends on changes
        ~update stuff();

        this.Invalidate();
        //this.Refresh();
    }
}

The control is contained in a panel on standard WinForm.

I have tried both Invalidate and Refresh.

When using the Invalidate () function, the control will correctly redraw as long as the form in which it is contained has focus. Drawing is smooth. When I switch focus to another shape, the pattern stops, even if events still fire, and this one. Invalidate () is still being called. The form is still fully visible on the screen.

Refresh() , , , .

, Invalidate OnPaint ?

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3

:

Invalidate ; , Update Invalidate .

Update Invalidate?

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Invalidate (true), .

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( ) . , , Refresh. - , . . ApplicationLoopDoWork , - . , .

Tom Miller.

, . ApplicationLoopDoWork.

    using System;
    using System.Runtime.InteropServices;
    using System.Threading;
    using System.Windows.Forms;

    namespace Utilities.UI
    {
    /// <summary>
    /// WinFormsAppIdleHandler implements a WinForms Render Loop (max FPS possible).
    /// Reference: http://blogs.msdn.com/b/tmiller/archive/2005/05/05/415008.aspx
    /// </summary>
    public sealed class WinFormsAppIdleHandler
    {
        private readonly object _completedEventLock = new object();
        private event EventHandler _applicationLoopDoWork;

        //PRIVATE Constructor
        private WinFormsAppIdleHandler()
        {
            Enabled = false;
            SleepTime = 10;

        }

        /// <summary>
        /// Singleton from:
        /// http://csharpindepth.com/Articles/General/Singleton.aspx
        /// </summary>
        private static readonly Lazy<WinFormsAppIdleHandler> lazy = new Lazy<WinFormsAppIdleHandler>(() => new WinFormsAppIdleHandler());
        public static WinFormsAppIdleHandler Instance { get { return lazy.Value; } }

        private bool _enabled = false;

        /// <summary>
        /// Gets or sets if must fire ApplicationLoopDoWork event.
        /// </summary>
        public bool Enabled
        {
            get { return _enabled; }
            set {
                if (value)
                    Application.Idle += Application_Idle;
                else
                    Application.Idle -= Application_Idle;

                _enabled = value;
            }
        }

        /// <summary>
        /// Gets or sets the minimum time betwen ApplicationLoopDoWork fires.
        /// </summary>
        public int SleepTime { get; set; }

        /// <summary>
        /// Fires while the UI is free to work. Sleeps for "SleepTime" ms.
        /// </summary>
        public event EventHandler ApplicationLoopDoWork
        {
            //Reason of using locks:
            //http://stackoverflow.com/questions/1037811/c-thread-safe-events
            add
            {
                lock (_completedEventLock)
                    _applicationLoopDoWork += value;
            }

            remove
            {
                lock (_completedEventLock)
                    _applicationLoopDoWork -= value;
            }
        }

        /// <summary>
        ///Application idle loop.
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void Application_Idle(object sender, EventArgs e)
        {
            //Try to update interface
            while (Enabled && IsAppIdle())
            {
                OnApplicationIdleDoWork(EventArgs.Empty);
                //Give a break to the processor... :)
                //8 ms -> 125 Hz
                //10 ms -> 100 Hz
                Thread.Sleep(SleepTime);
            }
        }

        private void OnApplicationIdleDoWork(EventArgs e)
        {
            var handler = _applicationLoopDoWork;
            if (handler != null)
            {
                handler(this, e);
            }
        }

        /// <summary>
        /// Gets if the app is idle.
        /// </summary>
        /// <returns></returns>
        public static bool IsAppIdle()
        {
            bool isIdle = false;
            try
            {
                Message msg;
                isIdle = !PeekMessage(out msg, IntPtr.Zero, 0, 0, 0);
            }
            catch (Exception e)
            {
                //Should never get here... I hope...
                MessageBox.Show("IsAppStillIdle() Exception. Message: " + e.Message);
            }
            return isIdle;
        }

        #region  Unmanaged Get PeekMessage
        // http://blogs.msdn.com/b/tmiller/archive/2005/05/05/415008.aspx
        [System.Security.SuppressUnmanagedCodeSecurity] // We won't use this maliciously
        [DllImport("User32.dll", CharSet = CharSet.Auto)]
        public static extern bool PeekMessage(out Message msg, IntPtr hWnd, uint messageFilterMin, uint messageFilterMax, uint flags);

        #endregion
    }
}
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