不知道为什么不能改变背景图

[SerionHu]

我用的是VS.NET 2005
在这中情况下不能改变,在调试时已经看到这一行以通过,就好想处理了也没反应:
this.BackgroundImage = back_error;

========================================
private void txtCommand_KeyPress(object sender, KeyPressEventArgs e)
{
if (e.KeyChar == 13)
{
try
{
System.Diagnostics.Process.Start(txtCommand.Text);
}
catch(Exception ex)
{
justError = true;
this.BackgroundImage = back_error;

txtCommand.Text = txtCommand.Text + " --*" + ex.Message + "*--";
}
}
}
================================================

但这中情况就有,可以看到背景改变了:

================================================
private void txtCommand_KeyPress(object sender, KeyPressEventArgs e)
{
this.BackgroundImage = back_error;

if (e.KeyChar == 13)
{
try
{
System.Diagnostics.Process.Start(txtCommand.Text);
}
catch(Exception ex)
{
justError = true;
txtCommand.Text = txtCommand.Text + " --*" + ex.Message + "*--";
}
}
}
================================================

到了这种又没有了(真搞不明白):

================================================
private void txtCommand_KeyPress(object sender, KeyPressEventArgs e)
{
if (e.KeyChar == 13)
{
try
{
System.Diagnostics.Process.Start(txtCommand.Text);
}
catch(Exception ex)
{
justError = true;
txtCommand.Text = txtCommand.Text + " --*" + ex.Message + "*--";
}
}

this.BackgroundImage = back_error;
}
============================================

请各位帮小弟看看这是个什么问题,先谢了!!

[Knight94]

窗体的paint事件中做什么处理了吗

[Qim]

this.invalidate()