Re: Instance from the active form - C# Discussion Boards

Judah Gabriel Himango31-Jul-06 5:12

Re: Instance from the active form [modified]

31-Jul-06 5:12

Ramez Quneibi wrote:
used a thread to process a button function inside my code

Could you elaborate on that a little bit? My guess is your problem has something to do with threading. You cannot access a control on a thread other than the one it was created on.

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Ramez Quneibi31-Jul-06 21:36

31-Jul-06 21:36

Here i am showing you snippets from my code to elaborate on the problem to you
These snippets form Form1 class :

static void Main()
{
Application.Run(new Form1());
}

private void button1_Click(object sender, System.EventArgs e)
{
System.Threading.Thread NewFormMaker = new System.Threading.Thread(new System.Threading.ThreadStart(Dummy));
NewFormMaker.Start();
}
public static void Dummy()
{
Form2 fmNew = new Form2();
fmNew.ShowDialog();
}
This is a snippet from Form2 class :

// When this button pressed from Form2 this function should create new
// form with new controls and close the previous one

private void Next_Click(object sender, System.EventArgs e)
{
// Create an instance from the active form to close it
Form2 tempForm=(Form2)Form2.ActiveForm;
// Call Dummy() function from Form1 to show the new results
Form1.Dummy();
// Close the previous form with the old results
tempForm.Close();
}

The problem is that i cant make an instance from the active form to close it when i press button next from Form2.

Thanx

I hope that i am helping programmers

-- modified at 3:42 Tuesday 1st August, 2006

Judah Gabriel Himango1-Aug-06 4:39

1-Aug-06 4:39

Ramez Quneibi wrote:
he problem is that i cant make an instance from the active form to close it when i press button next from Form2.

OK, a couple things worth mentioning here. If you need to pass an instance of form1 over to form2, add an argument to the Form2 constructor that stores the form1 instance:

class Form2
{
   readonly Form1 firstFormInstance;
   
   public Form2(Form1 instance)
   {
       this.firstFormInstance = instance;
   }
}

A second thing to note is that you cannot access a control or a form on a thread other than the one it was created on. Say you have Form1 instance created by "thread1". You start a new thread, "thread2" to launch a new Form2 instance. This is all valid, however, inside form2, you cannot access form1 because it was created by a different thread. If you need to do that, you'll need to use form1.Invoke or form1.BeginInvoke, which will invoke some method on the correct thread for form1.

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Ramez Quneibi1-Aug-06 21:26

1-Aug-06 21:26

I used these techniques you told me about ,it may work in other applications but it my code it didnt. I used another thread to show form2 from form1 but i didnt work because i am filling form2 from form1 class and if i make another thread i cant fill form2 from form1 class.
Anyways...I am using this technique to avoid the from freezing when i start the application because i have a very long process consumes 2 mins, the form in this duration freezes and stop me to do anything, if you can help me to give another technique i will appreciate .
Thanx alot .

Judah Gabriel Himango2-Aug-06 5:20

2-Aug-06 5:20

Ramez Quneibi wrote:
I am using this technique to avoid the from freezing when i start the application because i have a very long process consumes 2 mins

Don't use a 2nd thread to start the form. If the form itself is doing lots of work, have the form use a background thread to perform the work, thus keeping the UI thread free. You should never do any large amount of work on the UI thread. If you are, most likely you have designed your application incorrectly.

I recommend launching form2 from form1 using the same thread that's running form1. If form2 is doing lots of work, make form2 start a background thread to do the work.

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Ramez Quneibi4-Aug-06 5:22

4-Aug-06 5:22

what do you mean by background thread ? i put the process inside the button click event in a thread.

<br />
   private void button9_Click(object sender, System.EventArgs e)<br />
  {<br />
    new Thread(new ThreadStart(Search)).Start(); <br />
  }<br />
  private void Search()<br />
  {<br />
   // The whole process is here and in the final launch form2 <br />
  }<br />

Judah Gabriel Himango4-Aug-06 10:04

4-Aug-06 10:04

Ramez Quneibi wrote:
what do you mean by background thread ?

I mean a thread other than the UI thread. You did new Thread(new ThreadStart(Search)).Start(); that just started a background thread. Don't use a background thread to launch Form2. Launch Form2 from the UI thread. If you need to perform search work on a background thread, that's fine, but don't create a UI from you background thread.

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Ramez Quneibi4-Aug-06 22:47

4-Aug-06 22:47

ok, this works well, thanx alot

Copy an instance

sjembek31-Jul-06 4:30

31-Jul-06 4:30

Is it possible to make an exact copy of an instance of an object (not its reference)?

This is what I'd like to achieve:
1 make a copy of an instance at a certain moment to save the state it's in
2 modify the original for a bit
3 replace the original object with the saved one later on

This way I'd like to be able to "recall" the state my object was in at the moment I made a copy. Is this possible without manually constructing a new object of this type and copying all of it's members?

Dustin Metzgar31-Jul-06 4:44

Dustin Metzgar

31-Jul-06 4:44

To do this, you can binary serialize the object. Serialize the object to a memory stream and then deserialize to a new instance. For classes that don't have a CopyTo method, this is pretty helpful. However, the class that you're serializing has to have the Serializable attribute.

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sjembek31-Jul-06 5:50

31-Jul-06 5:50

Actually it is Serializable since it can be stored to disk too. I just had a go with this but I haven't serialized to memory before and for some reason I'm getting a

System.Runtime.Serialization.SerializationException: End of Stream encountered before parsing was completed.<br />

The code looks like this.

Collection<MyOutput> myOutputCollection = new Collection<MyOutput>();

BinaryFormatter bFormatter = new BinaryFormatter();

MemoryStream mStream = new MemoryStream();
OutputData myOutput;

bFormatter.Serialize(mStream, myOutput);
                
deserializedOutput = (OutputData)bFormatter.Deserialize(mStream);

myOutputCollection.add(deserializedOutput);

mStream.Close();

I'm serializing and deserializing the object, then adding it to a collection, since I'm still using it from the collection once it's added (it's not like I don't need it anymore).

Dustin Metzgar31-Jul-06 6:25

Dustin Metzgar

31-Jul-06 6:25

Before you deserialize, you have to rewind the memory stream back to the initial position.

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sjembek31-Jul-06 6:42

31-Jul-06 6:42

This works, thx Smile | :)

A.A.31-Jul-06 4:45

A.A.

31-Jul-06 4:45

In short you want something to that gives you an 'undo' feature. I don't like recommending 'design patterns' without looking at several alternatives, but in this case the Memento pattern fits well.

Googling will give you a solid explanation.

Wikipedia has a short code sample:
Memento pattern[^]

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sjembek31-Jul-06 5:35

31-Jul-06 5:35

I see the use of the pattern, but it seems this will only work for a single member that defines the state, while I meant the state of the object itself and all of its members... I'm afraid this won't work, but thanks for the info.

LongRange.Shooter31-Jul-06 5:12

LongRange.Shooter

31-Jul-06 5:12

You could do the following:

Make the following changes to your class:

public class MyClass : ICloneable
{
   public MyClass(){}
   public MyClass(object newInstance)
   {
       if ( !(newInstance is MyClass) ) throw new Exception...
       MyClass instance = (MyClass)newInstance;
       // set all properties to the values in the passed instance
   }
   public object Clone
   {
      return (object)this;
   {
}

Then in your code you would do as follows:

...
MyClass newObject = new MyClass(oldObject.Clone());

Unfortunately, there is no ICloneable<t> and object is all you can pass.

Judah Gabriel Himango31-Jul-06 5:29

31-Jul-06 5:29

Wesner Moise has a good blog posting[^] regarding how to clone objects that don't implement ICloneable. He basically uses reflection to invoke the protected MemberwiseClone method.

If you have the source code to this object, I'd just make it implement ICloneable.

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sjembek31-Jul-06 5:52

31-Jul-06 5:52

Looks interesting, I'll try this out...

sjembek31-Jul-06 6:43

31-Jul-06 6:43

Works perfectly... Thank you.