C#

while(true)
{
  line = streamReader.ReadLine();
  
  if(line == null)  // break condition
    break;
 
  ....  // rest of the loop
}

while(line = streamReader.ReadLine())
{  
// rest of the loop
}

Why not

while(line = streamReader.ReadLine()){  // rest of the loop}


??? 

if(line == null)
   break;

FileInfo fileInfo = new FileInfo(files[i]);
StreamReader streamReader = fileInfo.OpenText();

// Hela raden
string line;
do
{
line = streamReader.ReadLine();
// Does line contain "searchText"??
<font color="red">if ((line != null) && (line.IndexOf(searchText) != -1))</font>
{
listBox1.Items.Add(line);
}
}
while(line != null); 

protected override void WndProc(ref Message m)
{
  switch(m.Msg)
  {
  case 0x0112:  // WM_SYSCOMMAND
    if( m.WParam.ToInt32() == 0xF020 ) // WParam == SC_MINIMIZE
    {
      // Code to execute when minimizing
    }
 
    base.WndProc(ref m);  // Let the regular actions happen in addition to our action
    break;
 
  default:
    base.WndProc(ref m);
  }
}