Is there a graceful way in C# to delete multiple lines of text from the beginning of a multiline textbox? I am using Microsoft Visual C# 2008 Express Edition.
EDIT - Additional Details
The multiline textbox in my application is disabled (i.e. it is only editable by the application itself), and every line is terminated with a "\r\n".
This is an incomplete question. So assuming you are using either TextBox or RichTextBox you can use the Lines property found inTextBoxBase.
//get all the lines out as an arry
string[] lines = this.textBox.Lines;
You can then work with this array and set it back.
this.textBox.Lines= newLinesArray;
This might not be the most elegant way, but it will remove the first line.
EDIT: you don't need select, just using skip will be fine
//number of lines to remove from the beginning
int numOfLines = 30;
var lines = this.textBox1.Lines;
var newLines = lines.Skip(numOfLines);
this.textBox1.Lines = newLines.ToArray();
This solution works for me in WPF:
while (LogTextBox.LineCount > Constants.LogMaximumLines)
{
LogTextBox.Text = LogTextBox.Text.Remove(0, LogTextBox.GetLineLength(0));
}
You can replace LogTextBox with the name of your text box, and Constants.LogMaximumLines with the maximum number of lines you would like your text box to have.
Unfortunately, no, there is no "elegant" way to delete lines from the text of a multiline TextBox, regardless of whether you are using ASP.NET, WinForms, or WPF/Silverlight. In every case, you build a string that does not contain the lines you don't want and set the Text property.
WinForms will help you a little bit by pre-splitting the Text value into lines, using the Lines property, but it's not very helpful because it's a string array, and it's not exactly easy to delete an element of an array.
Generally, this algorithm will work for all possible versions of the TextBox class:
var lines = (from item in myTextBox.Text.Split('\n') select item.Trim());
lines = lines.Skip(numLinesToSkip);
myTextBox.Text = string.Join(Environment.Newline, lines.ToArray());
Note: I'm using Environment.Newline specifically for the case of Silverlight on a Unix platform. For all other cases, you're perfectly fine using "\r\n" in the string.Join call.
Also, I do not consider this an elegant solution, even though it's only 3 lines. What it does is the following:
splits the single string into an array of strings
iterates over that array and builds a second array that does not include the lines skipped
joins the array back into a single string.
I do not consider it elegant because it essentially builds two separate arrays, then builds a string from the second array. A more elegant solution would not do this.
One thing to keep in mind is that the Lines collection of the TextBox does not accurately reflect what the user sees as lines. The Lines collection basically works off of carriage returns, whereas the user could see lines wrapping from one line to the next without a carriage return. This may or may not be the behavior you want.
For example, the user would see the below as three lines, but the Lines collection will show 2 (since there are only 2 carriage returns):
This is line number
one.
This is line 2.
Also, if the form, and the text control are resizable the visible lines in the text will change as the control grows or shrinks.
I wrote a blog post several years ago on how to determine the number of lines in the textbox as the user sees them and get the index of a given line (like to get the line at index: http://ryanfarley.com/blog/archive/2004/04/07/511.aspx, perhaps this post will help.
if (txtLog.Lines.Length > maxNumberLines)
{
txtLog.Lines = txtLog.Lines.Skip(txtLog.Lines.Length - maxNumberLines).ToArray();
}
Related
I have this little project in C# where I am manipulating with files. Now my task is that I have to delete specific rows from files.
For example my file looks like this:
1-this is the first line
2-this is the second line
3-this is the third line
4-this is the fourth line
Now how can I keep only the first two rows and delete only the last two rows?
Note- this is how I read the file from my local machine:
string[] lines = File.ReadAllLines(#"C:\Users\admin\Desktop\COMMANDS.dat");
I have tried something like this but I think it's not so "efficient"
string text = File.ReadAllText(#"C:\Users\admin\Desktop\COMMANDS.dat");
text = text.Replace(lines[2], "");
text = text.Replace(lines[3], "");
File.WriteAllText(#"C:\Users\admin\Desktop\COMMANDS.dat", text);
So this actually does the job, it replaces the lines by string with an empty character but when I take a look at the file, I don't want to have 4 lines there, even though 2 of them are real strings and the other two are just empty lines... Can I manage to do this in another way?
Try replacing the newline character with an empty string:
string text = File.ReadAllText(#"C:\Users\admin\Desktop\COMMANDS.dat");
text = text.Replace(lines[2], "").Remove(Environment.NewLine, "");
text = text.Replace(lines[3], "").Remove(Environment.NewLine , "");
File.WriteAllText(#"C:\Users\admin\Desktop\COMMANDS.dat", text);
If my answer is useful, please mark it as accepted, and upvote it.
async Task Example()
{
var inputLines = await File.ReadAllLinesAsync("path/to/file.txt");
var outputLines = inputLines.Where((l, i) => i < 2);
await File.WriteAllLinesAsync("target/file.txt", outputLines);
}
What it does
Read data but not as one string but as a collection of lines
Create a new collection containing only the lines you want in your output
Write the filtered lines
Notes:
This example is not optimized for memory usage (because we read all lines and for larger files, e.g. multiple GB, this will fail). See existing answers for memory optimized version) - but: It's totally fine to do it this way if you know you have just a few k lines. (and it's faster)
Try not to "modify" strings. This will always create a copy and needs a lot of memory.
In this "Linq style" (functional) approach, we should treat data as immutable. That means: we have one variable that represents the input file and one variable that represents the result. We use declarative Linq to describe how the output should look like. "output is input where the filter index < 2 matches" instead of "if xy remove line" in an imperative style.
I am new to this site, and I don't know if I am providing enough info - I'll do my best =)
If you use Notepad++, then you will know what I am talking about -- When a user loads a .exe into Notepad++, the NUL / \x0 character is replaced by NULL, which has a black background, and white text. I tried pasting it into Visual Studio, hoping to obtain the same output, but it just pasted some spaces...
Does anyone know if this is a certain key-combination, or something? I would like to put the NULL character in replacement of \x0, just like Notepad++ =)
Notepad++ is a rich text editor unlike your regular notepad. It can display custom graphics so common in all modern text editors. While reading a file whenever notepad++ encounters the ASCII code of a null character then instead of displaying nothing it adds the string "NULL" to the UI setting the text background colour to black and text colour to white which is what you are seeing. You can show any custom style in your rich text editor too.
NOTE: This is by no means an efficient solution. I'm clearly traversing a read string 2 times just to take benefit of already present methods. This can be done manually in a single pass. It is just to give a hint about how you can do it. Also I wrote the code carefully but haven't ran it because I don't have the tools at the moment. I apologise for any mistakes let me know I'll update it
Step 1 : Read a text file by line (line ends at '\n') and replace all instances of null character of that line with the string "NUL" using the String.Replace(). Finally append the modified text to your RichTextBox.
Step 2 : Re traverse your read line using String.IndexOf() finding start indexes of each "NUL" word. Using these indexed you select text from RichTextBox and then style that selected text using RichTextBox.SelectionColor and RichTextBox.SelectionBackColor
richTextBoxCursor basically just represents the start index of each line in RichTextBox
StreamReader sr = new StreamReader(#"c:\test.txt" , Encoding.UTF8);
int richTextBoxCursor = 0;
while (!sr.EndOfStream){
richTextBoxCursor = richTextBox.TextLength;
string line = sr.ReadLine();
line = line.Replace(Convert.ToChar(0x0).ToString(), "NUL");
richTextBox.AppendText(line);
i = 0;
while(true){
i = line.IndexOf("NUL", i) ;
if(i == -1) break;
// This specific select function select text start from a certain start index to certain specified character range passed as second parameter
// i is the start index of each found "NUL" word in our read line
// 3 is the character range because "NUL" word has three characters
richTextBox.Select(richTextBoxCursor + i , 3);
richTextBox.SelectionColor = Color.White;
richTextBox.SelectionBackColor = Color.Black;
i++;
}
}
Notepad++ may use custom or special fonts to show these particular characters. This behavior also may not appropriate for all text editors. So, they don't show them.
If you want to write a text editor that visualize these characters, you probably need to implement this behavior programmatically. Seeing notepad++ source can be helpful If you want.
Text editor
As far as I know in order to make Visual Studio display non printable characters you need to install an extension from the marketplace at https://marketplace.visualstudio.com.
One such extension, which I have neither tried nor recomend - I just did a quick search and this is the first result - is
Invisible Character Visualizer.
Having said that, copy-pasting binaries is a risky business.
You may try Edit > Advanced > View White Space first.
Binary editor
To really see what's going on you could use the VS' binary editor: File->Open->(Open with... option)->Binary Editor -> OK
To answer your question.
It's a symbolic representation of 00H double byte.
You're copying and pasting the values. Notepad++ is showing you symbols that replace the representation of those values (because you configured it to do so in that IDE).
Working on a program that takes a CSV file and splits on each ",". The issue I have is there are thousand separators in some of the numbers. In the CSV file, the numbers render correctly. When viewed as a text document, they are shown like below:
Dog,Cat,100,100,Fish
In a CSV file, there are four cells, with the values "Dog", "Cat", "100,000", "Fish". When I split on the "," to an array of strings, it contains 5 elements, when what I want is 4. Anyone know a way to work around this?
Thanks
There are two common mistakes made when reading csv code: using a split() function and using regular expressions. Both approaches are wrong, in that they are prone to corner cases such as yours and slower than they could be.
Instead, use a dedicated parser such as Microsoft.VisualBasic.TextFieldParser, CodeProject's FastCSV or Linq2csv, or my own implemention here on Stack Overflow.
Typically, CSV files would wrap these elements in quotes, causing your line to be displayed as:
Dog,Cat,"100,100",Fish
This would parse correctly (if using a reasonable method, ie: the TextFieldParser class or a 3rd party library), and avoid this issue.
I would consider your file as an error case - and would try to correct the issue on the generation side.
That being said, if that is not possible, you will need to have more information about the data structure in the file to correct this. For example, in this case, you know you should have 4 elements - if you find five, you may need to merge back together the 3rd and 4th, since those two represent the only number within the line.
This is not possible in a general case, however - for example, take the following:
100,100,100
If that is 2 numbers, should it be 100100, 100, or should it be 100, 100100? There is no way to determine this without more information.
you might want to have a look at the free opensource project FileHelpers. If you MUST use your own code, here is a primer on the CSV "standard" format
well you could always split on ("\",\"") and then trim the first and last element.
But I would look into regular expressions that match elements with in "".
Don't just split on the , split on ", ".
Better still, use a CSV library from google or codeplex etc
Reading a CSV file in .NET?
You may be able to use Regex.Replace to get rid of specifically the third comma as per below before parsing?
Replaces up to a specified number of occurrences of a pattern specified in the Regex constructor with a replacement string, starting at a specified character position in the input string. A MatchEvaluator delegate is called at each match to evaluate the replacement.
[C#] public string Replace(string, MatchEvaluator, int, int);
I ran into a similar issue with fields with line feeds in. Im not convinced this is elegant, but... For mine I basically chopped mine into lines, then if the line didnt start with a text delimeter, I appended it to the line above.
You could try something like this : Step through each field, if the field has an end text delimeter, move to the next, if not, grab the next field, appaend it, rince and repeat till you do have an end delimeter (allows for 1,000,000,000 etc) ..
(Im caffeine deprived, and hungry, I did write some code but it was so ugly, I didnt even post it)
Do you know that it will always contain exactly four columns? If so, this quick-and-dirty LINQ code would work:
string[] elements = line.Split(',');
string element1 = elements.ElementAt(0);
string element2 = elements.ElementAt(1);
// Exclude the first two elements and the last element.
var element3parts = elements.Skip(2).Take(elements.Count() - 3);
int element3 = Convert.ToInt32(string.Join("",element3parts));
string element4 = elements.Last();
Not elegant, but it works.
I have a program that generates a plain text file. The structure (layout) is always the same. Example:
Text File:
LinkLabel
"Hello, this text will appear in a LinkLabel once it has been
added to the form. This text may not always cover more than one line. But will always be surrounded by quotation marks."
240, 780
So, to explain what is going on in that file:
Control
Text
Location
And when a button on the Form is clicked, and the user opens one of these files from the OpenFileDialog dialog, I need to be able to Read each line. Starting from the top, I want to check to see what control it is, then starting on the second line I need to be able to get all text inside the quotation marks (regardless of whether is is one line of text or more), and on the next line (after the closing quotation mark), I need to extract the location (240, 780)... I have thought of a few ways of going about this but when I go to write it down and put it to practice, it doesn't make much sense and end up figuring out ways that it won't work.
Has anybody ever done this before? Would anybody be able to provide any help, suggestions or advice on how I'd go about doing this?
I have looked up CSV files but that seems too complicated for something that seems so simple.
Thanks
jase
You could use a regular expression to get the lines from the text:
MatchCollection lines = Regex.Matches(File.ReadAllText(fileName), #"(.+?)\r\n""([^""]+)""\r\n(\d+), (\d+)\r\n");
foreach (Match match in lines) {
string control = match.Groups[1].Value;
string text = match.Groups[2].Value;
int x = Int32.Parse(match.Groups[3].Value);
int y = Int32.Parse(match.Groups[4].Value);
Console.WriteLine("{0}, \"{1}\", {2}, {3}", control, text, x, y);
}
I'll try and write down the algorithm, the way I solve these problems (in comments):
// while not at end of file
// read control
// read line of text
// while last char in line is not "
// read line of text
// read location
Try and write code that does what each comment says and you should be able to figure it out.
HTH.
You are trying to implement a parser and the best strategy for that is to divide the problem into smaller pieces. And you need a TextReader class that enables you to read lines.
You should separate your ReadControl method into three methods: ReadControlType, ReadText, ReadLocation. Each method is responsible for reading only the item it should read and leave the TextReader in a position where the next method can pick up. Something like this.
public Control ReadControl(TextReader reader)
{
string controlType = ReadControlType(reader);
string text = ReadText(reader);
Point location = ReadLocation(reader);
... return the control ...
}
Of course, ReadText is the most interesting one, since it spans multiple lines. In fact it's a loop that calls TextReader.ReadLine until the line ends with a quotation mark:
private string ReadText(TextReader reader)
{
string text;
string line = reader.ReadLine();
text = line.Substring(1); // Strip first quotation mark.
while (!text.EndsWith("\"")) {
line = reader.ReadLine();
text += line;
}
return text.Substring(0, text.Length - 1); // Strip last quotation mark.
}
This kind of stuff gets irritating, it's conceptually simple, but you can end up with gnarly code. You've got a comparatively simple case:one record per file, it gets much harder if you have lots of records, and you want to deal nicely with badly formed records (consider writing a parser for a language such as C#.
For large scale problems one might use a grammar driven parser such as this: link text
Much of your complexity comes from the lack of regularity in the file. The first field is terminated by nwline, the second by delimited by quotes, the third terminated by comma ...
My first recomendation would be to adjust the format of the file so that it's really easy to parse. You write the file so you're in control. For example, just don't have new lines in the text, and each item is on its own line. Then you can just read four lines, job done.
I am designing a crawler which will get certain content from a webpage (using either string manipulation or regex).
I'm able to get the contents of the webpage as a response stream (using the whole httpwebrequest thing), and then for testing/dev purposes, I write the stream content to a multi-line textbox in my ASP.NET webpage.
Is it possible for me to loop through the content of the textbox and then say "If textbox1.text.contains (or save the textbox text as a string variable), a certain string then increment a count". The problem with the textbox is the string loses formatting, so it's in one long line with no line breaking. Can that be changed?
I'd like to do this rather than write the content to a file because writing to a file means I would have to handle all sorts of external issues. Of course, if this is the only way, then so be it. If I do have to write to a file, then what's the best strategy to loop through each and every line (I'm a little overwhelmed and thus confused as there's many logical and language methods to use), looking for a condition? So if I want to look for the string "Hello", in the following text:
My name is xyz
I am xyz years of age
Hello blah blah blah
Bye
When I reach hello I want to increment an integer variable.
Thanks,
In my opinion you can split the content of the text in words instead of lines:
public int CountOccurences(string searchString)
{
int i;
var words = txtBox.Text.Split(" ");
foreach (var s in words)
if (s.Contains(searchString))
i++;
return i;
}
No need to preserve linebreaks, if I understand your purpose correctly.
Also note that this will not work for multiple word searches.
I do it this way in an project, there may be a better way to do it, but this works :)
string template = txtTemplate.Text;
string[] lines = template.Split(Environment.NewLine.ToCharArray());
That is a nice creative way.
However, I am returning a complex HTML document (for testing purposes, I am using Microsoft's homepage so I get all the HTML). Do I not have to specify where I want to break the line?
Given your method, if each line is in a collection (Which is a though I had), then I can loop through each member of the collection and look for the condition I want.
If textbox contents were returned with line-breaks representing where word-wrapping occurs, that result will be dependant on style (e.g. font-size, width of the textbox, etc.) rather than what the user actually entered. Depending on what you actually want to do, this is almost certainly NOT what you want.
If the user physically presses the 'carriage return / enter' key, the relevant character(s) will be included in the string.
Why do you need to have a textbox at all? Your real goal is to increment a counter based on the text that the crawler finds. You can accomplish this just by examining the stream itself:
Stream response = webRequest.GetResponse().GetResponseStream();
StreamReader reader = new StreamReader(response);
String line = null;
while ( line = reader.ReadLine() )
{
if (line.Contains("hello"))
{
// increment your counter
}
}
Extending this if line contains more than one instance of the string in question is left as an exercise to the reader :).
You can still write the contents to a text box if you want to examine them manually, but attempting to iterate over the lines of the text box is simply obscuring the problem.
The textbox was to show the contents of the html page. This is for my use so if I am running the webpage without any breakpoints, I can see if the stream is visually being returned. Also, it's a client requirement so they can see what is happening at every step. Not really worth the extra lines of code but it's trivial really, and the last of my concerns.
The code in the while loop I don't understand. Where is the instruction to go to the next line? This is my weakness with the readline method, as I seldom see the logic that forces the next line to be read.
I do need to store the line as a string var where a certain string is found, as I will need to do some operations (et a certain part of the string) so I've always been looking at readline.
Thanks!