How to get parent form in inherited user control

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Form parent = (Form)FindForm();

this works in class DropDownTextBox : UserControl
but I use this in class DropDownText : System.Windows.Forms.TextBox
it returns null

I just wants location of parent form when it moved
Thanks in advance.

Posted 6-Jan-14 21:02pm

Sid_Joshi

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Comments

Alexander Dymshyts 7-Jan-14 3:30am

can you provide more code? it's hard to understand what you mean

Sid_Joshi 7-Jan-14 4:15am

AutoSuggest is a User control I wants to build
Please help me to build
thanks in advance

Sid_Joshi 7-Jan-14 3:53am

namespace WindowsFormsApplication2
{
public partial class AutoSuggest : System.Windows.Forms.TextBox
{
public AutoSuggest()
{
InitializeComponent();
initControl();
}
int index = -1;
ListBox listBox1;
Form f3;
private DataTable dt;
Form parent;
public DataTable DataSource
{
get { return dt; }
set { dt = value; }
}

protected void initControl()
{
listBox1 = new ListBox();
listBox1.KeyDown += new KeyEventHandler(listBox1_KeyDown);
listBox1.DoubleClick += new EventHandler(listBox1_DoubleClick);
f3 = new Form();
f3.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;
f3.ShowInTaskbar = false;
f3.StartPosition = System.Windows.Forms.FormStartPosition.Manual;
this.KeyDown += new KeyEventHandler(textBox1_KeyDown);
this.TextChanged += new EventHandler(textBox1_TextChanged);
parent = (Form)FindForm();
//parent.Resize += new EventHandler(parent_Resize);
//parent.ResizeEnd += new EventHandler(parent_ResizeEnd);
//parent.Move += new EventHandler(parent_Move);
listBox1.Click += new EventHandler(listBox1_Click);
}

private void listBox1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Enter)
{
this.Text = listBox1.Text;
this.Select(this.Text.Length, 0);
listBox1.Items.Clear();
index = -1;
//listBox1.Visible = false;
removeComp();
}
}
private void listBox1_DoubleClick(object sender, EventArgs e)
{
this.Text = listBox1.Text;
this.Select(this.Text.Length, 0);
listBox1.Items.Clear();
index = -1;
//listBox1.Visible = false;
removeComp();
}
public void putComp()
{
Point location = this.PointToScreen(Point.Empty);
int x = location.X-1;
int y = location.Y + this.Height-2; //Down to textBox
//int y = textBox1.Location.Y -95; //Up to textBox

//int y = this.Location.Y + textBox1.Location.Y + textBox1.Height + 22;

f3.Location = new System.Drawing.Point(x, y);

f3.Width = this.Width;
f3.Height = 200;
//listBox1.Location = new System.Drawing.Point(0, 0);
listBox1.Dock = System.Windows.Forms.DockStyle.Fill;
f3.TopMost = true;
f3.Show();
f3.Controls.Add(listBox1);
this.Focus();

}
public void removeComp()
{

f3.Hide();
f3.Controls.Remove(listBox1);
index = -1;
}

private void textBox1_KeyDown(object sender, KeyEventArgs e)
{
if (listBox1.Items.Count > 0)
{
if (e.KeyCode == Keys.Down)
{
index++;
if (index >= listBox1.Items.Count - 1)
{
index = listBox1.Items.Count - 1;

}
}
if (e.KeyCode == Keys.Up)
{

index--;
if (index <= 0)
{
index = 0;

}
//textBox1.Select(textBox1.TextLength, 0);
e.SuppressKeyPress = true;

}

listBox1.SelectedIndex = index;

if (e.KeyCode == Keys.Enter)
{
this.Text = listBox1.Text;
this.Select(this.Text.Length, 0);

listBox1.Items.Clear();
index = -1;

Sid_Joshi 7-Jan-14 4:10am

//listBox1.Visible =false;
removeComp();
}
}
}

private void textBox1_TextChanged(object sender, EventArgs e)
{
listBox1.Items.Clear();

if (this.TextLength != 0)
{
//listBox1.Visible = true;
putComp();

DataRow[] dr = dt.Select(dt.Columns[0].Caption + " like '" + this.Text + "%'");
foreach (DataRow row in dr)
{
listBox1.Items.Add(row[0].ToString());
}

}
else
//listBox1.Visible = false;
removeComp();
}

private void parent_Resize(object sender, EventArgs e)
{
if (listBox1.Items.Count > 0)
{
removeComp();
putComp();
}
}
private void parent_ResizeEnd(object sender, EventArgs e)
{
if (listBox1.Items.Count > 0)
{
removeComp();
putComp();
}
}
private void parent_Move(object sender, EventArgs e)
{
if (listBox1 != null)
{
if (listBox1.Items.Count > 0)
{
removeComp();
putComp();
}
}
}
private void listBox1_Click(object sender, EventArgs e)
{
parent.Focus();
}

}
}

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OriginalGriff · Answer 1 · 2014-01-06T21:55:00

Solution 1

Don't. It's a poor idea from an OOPs point of view, because the control should not know what it is embedded into.
Instead, the parent form should feed information to the user control when it needs updating, or if the functionality of the control absolutely requires access to it's containing form information, then it should be passed with the control constructor.

Posted 6-Jan-14 21:55pm

OriginalGriff

Comments

Sid_Joshi 7-Jan-14 4:25am

Can u explain me with code?

OriginalGriff 7-Jan-14 4:47am

Explain which bit?

Sid_Joshi 7-Jan-14 5:08am

I can't understand what you wants to talk.

OriginalGriff 7-Jan-14 5:10am

Sorry - I'll try to explain more clearly.
"Can u explain me with code?"
Which part of the operation do you need explained?

Sid_Joshi 7-Jan-14 7:45am

namespace WindowsFormsApplication2
{
public partial class AutoSuggest : System.Windows.Forms.TextBox
{
public AutoSuggest()
{
InitializeComponent();
initControl();
}
int index = -1;
ListBox listBox1;
Form f3;
private DataTable dt;
Form parent;
public DataTable DataSource
{
get { return dt; }
set { dt = value; }
}

protected void initControl()
{
listBox1 = new ListBox();
listBox1.KeyDown += new KeyEventHandler(listBox1_KeyDown);
listBox1.DoubleClick += new EventHandler(listBox1_DoubleClick);
f3 = new Form();
f3.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;
f3.ShowInTaskbar = false;
f3.StartPosition = System.Windows.Forms.FormStartPosition.Manual;
this.KeyDown += new KeyEventHandler(textBox1_KeyDown);
this.TextChanged += new EventHandler(textBox1_TextChanged);
parent = (Form)FindForm();
//parent.Resize += new EventHandler(parent_Resize);
//parent.ResizeEnd += new EventHandler(parent_ResizeEnd);
//parent.Move += new EventHandler(parent_Move);
listBox1.Click += new EventHandler(listBox1_Click);
}

private void listBox1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Enter)
{
this.Text = listBox1.Text;
this.Select(this.Text.Length, 0);
listBox1.Items.Clear();
index = -1;
//listBox1.Visible = false;
removeComp();
}
}
private void listBox1_DoubleClick(object sender, EventArgs e)
{
this.Text = listBox1.Text;
this.Select(this.Text.Length, 0);
listBox1.Items.Clear();
index = -1;
//listBox1.Visible = false;
removeComp();
}
public void putComp()
{
Point location = this.PointToScreen(Point.Empty);
int x = location.X-1;
int y = location.Y + this.Height-2; //Down to textBox
//int y = textBox1.Location.Y -95; //Up to textBox

//int y = this.Location.Y + textBox1.Location.Y + textBox1.Height + 22;

f3.Location = new System.Drawing.Point(x, y);

f3.Width = this.Width;
f3.Height = 200;
//listBox1.Location = new System.Drawing.Point(0, 0);
listBox1.Dock = System.Windows.Forms.DockStyle.Fill;
f3.TopMost = true;
f3.Show();
f3.Controls.Add(listBox1);
this.Focus();

}
public void removeComp()
{

f3.Hide();
f3.Controls.Remove(listBox1);
index = -1;
}

private void textBox1_KeyDown(object sender, KeyEventArgs e)
{
if (listBox1.Items.Count > 0)
{
if (e.KeyCode == Keys.Down)
{
index++;
if (index >= listBox1.Items.Count - 1)
{
index = listBox1.Items.Count - 1;

}
}
if (e.KeyCode == Keys.Up)
{

index--;
if (index <= 0)
{
index = 0;

}
//textBox1.Select(textBox1.TextLength, 0);
e.SuppressKeyPress = true;

}

listBox1.SelectedIndex = index;

if (e.KeyCode == Keys.Enter)
{
this.Text = listBox1.Text;
this.Select(this.Text.Length, 0);

listBox1.Items.Clear();
index = -1;
//listBox1.Visible =

Sid_Joshi 7-Jan-14 7:47am

false;
removeComp();
}
}
}

private void textBox1_TextChanged(object sender, EventArgs e)
{
listBox1.Items.Clear();

if (this.TextLength != 0)
{
//listBox1.Visible = true;
putComp();

DataRow[] dr = dt.Select(dt.Columns[0].Caption + " like '" + this.Text + "%'");
foreach (DataRow row in dr)
{
listBox1.Items.Add(row[0].ToString());
}

}
else
//listBox1.Visible = false;
removeComp();
}

private void parent_Resize(object sender, EventArgs e)
{
if (listBox1.Items.Count > 0)
{
removeComp();
putComp();
}
}
private void parent_ResizeEnd(object sender, EventArgs e)
{
if (listBox1.Items.Count > 0)
{
removeComp();
putComp();
}
}
private void parent_Move(object sender, EventArgs e)
{
if (listBox1 != null)
{
if (listBox1.Items.Count > 0)
{
removeComp();
putComp();
}
}
}
private void listBox1_Click(object sender, EventArgs e)
{
parent.Focus();
}

}
}
in ths user control code i m trying to find parent form bt it returns null

OriginalGriff 7-Jan-14 8:56am

Well, the real question is "why?". Why do you want to know if the parent form has been resized? If it has, how does that affect you directly? If the parent needs you to change size for any reason, then it is responsible for "making you fit" - and there is a mechanism for that. If you are reacting to changes in the form, then what happens when your control is embedded in my control? If the form my control is embedded in changes size, my control may not, so any reaction to the form size change is outside your controls purview - the form is responsible for instructing controls to change size, not the control to react to changes in a form.

To do otherwise restricts the re-usability of your control, and also makes the whole application more tightly bound and harder to maintain. You should not be making decisions for outside elements!

Sid_Joshi 8-Jan-14 0:52am

Thanks for suggestion
I wants to show ListBox with auto suggest list options under the TextBox but I cant find out the Location for placing ListBox.
You are right it's tightly coupled task but how we can manage this by other way?