C#创建启动画面

文章来源：http://www.codeproject.com/Articles/3542/How-to-do-Application-Initialization-while-showing?rp=/KB/cs/AppLoadingArticle/AppLoading1.zip

• Version A (Quick 'n Dirty):Download demo project - 32 Kb
• Version B (MultiThreaded):Download demo project - 32 Kb

Update 28.01.03

This article has been updated withChris Austin'ssuggestion (Thanks Chris! And thanks toPhil Bolducfor the fix on Chris' stuff ;)) and an alternative (multithreaded) approach has been added, based onJabesidea (Thanks Jabes!).

Introduction

This articles shows how to display a splash screen during your application initialization. This article assumes that you familiar with C# and the VS.NET IDE.

Background

I had put the lot of my initialization code into the main formsOnLoad()override. The code parsed configuration files, created control and the such. When my application started up, it looked like a mess: The main application form just didn't pop up nicely and ready to be used. I decided to create a Splash Screen, which should pop up right after starting the executable. While the splash screen was shown, I wanted to do my initialization and once that was done, I'd hide the splash screen and show the main application window. This article contains various approaches on how it can be realized.

Version A: Quick 'n Dirty

This version was the quick and dirty solution I came up with. Credits toChris Austinfor suggesting the usage of theApplicationContextclass.

Preparations

1. Create a new empty Windows Forms project.
2. Add a new Form (for your splash screen and name it SplashForm).

1. Moving the Applications entry procedure

This is not required, but helps a beginning developer understand that theMain()entry point and the Form1 class into which it is put by default are not necessarily coupled. So let's create a new class called AppLoader and put the entry point in there. Once done, the class should look like this:

public class AppLoader
{
	public AppLoader()
	{
	}
	[STAThread]
	static void Main()
	{
	}
}

Once completed, remove the code from your Form1.cs so that you don't end up having 2 entry points.

2. Creating the Splash Screen

Just create a new Windows Form, place a PictureBox on it and set a couple of properties just to make it look nicer. The form should be centered on the screen (StartPosition), be topmost (TopMost) and shouldn't have a border (FormBorderStyle). As for the PictureBox, set theDockproperty to Fill and set theImageproperty to your splash image. That's it. In real life, you might want to write some code to display the application name, it's version, the registered user and a copyright notice, etc.

3. Modifying the MainForm's code

Now we need to do some modifications to the Form1 class. Since some initialization code can be put into the class constructor (such as reading files, etc.) some can't (like creating controls) sincethisis not available in the constructor. So you can't for example add controls to a formsControlscollection. Lets add a new public method (e.g.public void PreLoad(){...}). This function should look somewhat like this:

public void PreLoad()
{
	if (_Loaded)
	{
		//	just return. this code can't execute twice!
		return;
	}

	//	do your initialization here
	//	...

	//	flag that we have loaded all we need.
	_Loaded = true;
}

The_Loadedvariable is a private bool, which should be initialized tofalse. You definitely should check this flag in your main formsOnLoad()override (which is called just before the form is shown the first time). For example:

protected override void OnLoad(System.EventArgs e)
{
	if (!_Loaded)
	{
		//	good idea to throw an exception here. 
        //    the form shouldn't be shown w/o being initialized!
		return;
	}
}

4. Modifying the AppLoader class

Here is the code for theAppLoaderclass. See the comments for information.

public class AppLoader
{
	private static ApplicationContext context;
	private static SplashForm sForm = new SplashForm();
	private static MainForm mForm  = new MainForm();
	[STAThread]

	static void Main(string[] args)
	{
		//	first we retrieve an application context for usage in the 
        //    OnAppIdle event handler
		context = new ApplicationContext();

		//	then we subscribe to the OnAppIdle event...
		Application.Idle += new EventHandler(OnAppIdle);

		//	...and show our SplashForm
		sForm.Show();

		//	instead of running a window, we use the context
		Application.Run(context);
	}

	private static void OnAppIdle(object sender, EventArgs e)
	{
		if(context.MainForm == null)
		{
			//	first we remove the eventhandler
			Application.Idle -= new EventHandler(OnAppIdle);

			//	here we preload our form
			mForm.PreLoad();

			//	now we set the main form for the context...
			context.MainForm = mForm;

			//	...show it...
			context.MainForm.Show();

			//	...and hide the splashscreen. done!
			sForm.Close();
			sForm = null;
		}
	}
}

Version B: Multithreaded

This version entirely based onJabesidea. For more information read the Messages below. Thanks again to Jabes for letting me use his stuff in this article!

In this version, the SplashForm is shown in a separate thread and displays the current loading status (like in PhotoShop). You will want to multi-thread your splash screen if it is going to be on-screen for any length of time; by running the splash screen from its own message pump, screen redraws and other windows messages are processed correctly giving a more professional impression.

Preparations

1. Create a new empty Windows Forms project.
2. Add a new Form (for your splash screen and name it SplashForm).
3. Repeat the steps from the previous Section which create the AppLoader class containing the entry point for the application. Leave the Method Body forMain()empty for now. Don't forget to remove theMain()method from the Form1 code!

1. Modify the SplashForm

In order to display the loading status on the form, we need to place a label on the form. For our example we call it lStatusInfo. Additionally we create a get/set Property named StatusInfo. After that we introduce a private string member called _StatusInfo which maps directly to the Property. The Property implementation should look like this:

public string StatusInfo {
	set {
		_StatusInfo = value;
		ChangeStatusText();
	}
	get {
		return _StatusInfo;
	}
}

ChangeStatusText()is a helper function which will be called each time the StatusInfo should be updated. It's implementation should look like this:

public void ChangeStatusText() {
	try {
		if (this.InvokeRequired) {
			this.Invoke(new MethodInvoker(this.ChangeStatusText));
			return;
		}

		lStatusInfo.Text = _StatusInfo;
	}
	catch (Exception e) {
		//	do something here...
	}
}

The check for theInvokeRequiredproperty is necessary because controls are not thread safe. So if you call a method on a control from a different thread (then the one which created the control) without marshalling the call into the proper thread, weird things might happen.

That's it. Let's create the Splasher class which maintains Thread creation, start and stop.

2. Creating the Splasher class

The static membersShow(),Close()and theStatusproperty can be used as their names suggest to show and close the SplashWindow as well as to update the loading status displayed on the SplashForm (using theStatusInfoProperty previously created).

Here is what the implementation of the class looks like:

public class Splasher
{
	static SplashForm MySplashForm = null;
	static Thread MySplashThread = null;

	//	internally used as a thread function - showing the form and
	//	starting the messageloop for it
	static void ShowThread()
	{
		MySplashForm = new SplashForm();
		Application.Run(MySplashForm);
	}

	//	public Method to show the SplashForm
	static public void Show()
	{
		if (MySplashThread != null)
			return;

		MySplashThread = new Thread(new ThreadStart(Splasher.ShowThread));
		MySplashThread.IsBackground = true;
		MySplashThread.ApartmentState = ApartmentState.STA;
		MySplashThread.Start();
	}

	//	public Method to hide the SplashForm
	static public void Close()
	{
		if (MySplashThread == null) return;
		if (MySplashForm == null) return;

		try
		{
			MySplashForm.Invoke(new MethodInvoker(MySplashForm.Close));
		}
		catch (Exception)
		{
		}
		MySplashThread = null;
		MySplashForm = null;
	}

	//	public Method to set or get the loading Status
	static public string Status
	{
		set
		{
			if (MySplashForm == null)
			{
				return;
			}

			MySplashForm.StatusInfo = value;
		}
		get
		{
			if (MySplashForm == null)
			{
				throw new InvalidOperationException("Splash Form not on screen");
			}
			return MySplashForm.StatusInfo;
		}
	}
}

Ok, let’s look at what we have here:

TheShow()method will create a new Thread using the staticShowThreadfunction as a target. This function will simply show the Form and start a MessageLoop for it. TheClose()method will again marshal a call to the SplashFormsClose()method into the appropriate thread thus causing the form to close. TheStatusProperty can be used to retrieve or update the StatusInfo displayed on the SplashScreen.

Here are some simple examples of their usage:

...
	//	note that there is no instance required since those functions are static
	Splasher.Show();	//	shows the SplashScreen
        //	sets the status info displayed on the SplashScreen
	Splasher.Status = "Initializing Database Connection...";	
	Splasher.Close();	//	closes the SplashScreen
...

Modifying the AppLoader class

In order to use the Splasher class we have to modify our AppLoader class appropriately:

public class AppLoader
{
	public AppLoader()
	{

	}
	[STAThread]
	static void Main(string[] args)
	{
		Splasher.Show();
		DoStartup(args);
		Splasher.Close();
	}

	static void DoStartup(string[] args)
	{
		//	do whatever you need to do
		Form1 f = new Form1();
		Application.Run(f);
	}
}

First we show theSplashFormand set the initialStatusInfotext. Then we callDoStartup(), a good place to put any initialization code which doesn't require a form to be created.

Why moving the Startup Code into an extra function you might ask. The answer is simple: Since the Jitter works on a per function basis, it won’t need to do too much code before your Splash-Screen is actually getting shown on the screen.

To ensure that after you main Application form is loaded, it actually gets focused; you might want to put the following statement into the Form1OnLoadoverride:

this.Activate();