    if (string.IsNullOrEmpty(myString)) {
       //
    }

Since .NET 2.0 you can use:

    // Indicates whether the specified string is null or an Empty string.
    string.IsNullOrEmpty(string value);

Additionally, since .NET 4.0 there&#39;s a new method that goes a bit farther:

    // Indicates whether a specified string is null, empty, or consists only of white-space characters.
    string.IsNullOrWhiteSpace(string value);



if the variable is a string

    bool result = string.IsNullOrEmpty(variableToTest);

if you only have an object which may or may not contain a string then 

    bool result = string.IsNullOrEmpty(variableToTest as string);

Cheap trick:

    Convert.ToString((object)stringVar) == &quot;&quot;

This works because `Convert.ToString(object)` returns an empty string if `object` is null. `Convert.ToString(string)` returns null if `string` is null.

(Or, if you&#39;re using .NET 2.0 you could always using `String.IsNullOrEmpty`.)

    if (string.IsNullOrEmpty(myString)) 
    {
      . . .
      . . .
    }

I am using jQuery to create custom radio buttons and i have a problem.
When clicking on the label that associated with the radio the click events fires twice, if i click only on the radio itself it&#39;s working fine (well actually it&#39;s not the radio i am clicking but the div that wraps the whole input and label). Here is the code:

The HTML:

     &lt;div id=&quot;box&quot;&gt;
         &lt;asp:RadioButtonList ID=&quot;RadioButtonList1&quot; runat=&quot;server&quot;&gt;
             &lt;asp:ListItem&gt;RADIO1&lt;/asp:ListItem&gt;
             &lt;asp:ListItem&gt;RADIO2&lt;/asp:ListItem&gt;
             &lt;asp:ListItem&gt;RADIO3&lt;/asp:ListItem&gt;
         &lt;/asp:RadioButtonList&gt;
    &lt;/div&gt;

jQuery:

    &lt;script type=&quot;text/javascript&quot;&gt;
           $(function () {
                $(&#39;#box&#39;).find(&#39;input:radio&#39;).each(function (i) {
    
                var input = $(this);
                // get the associated label using the input&#39;s id
                var label = $(&#39;label[for=&#39; + input.attr(&#39;id&#39;) + &#39;]&#39;);
                // wrap the input + label in a div
                $(&#39;&lt;div class=&quot;custom-radio&quot;&gt;&lt;/div&gt;&#39;).insertBefore(input).append(label, input);
    
                var wrapperDiv = input.parent();
    
                // find all inputs in this set using the shared name attribute
                var allInputs = $(&#39;input[name=&#39; + input.attr(&#39;name&#39;) + &#39;]&#39;);
    
                // necessary for browsers that don&#39;t support the :hover pseudo class on labels
                label.hover(
    
                function () {
                    $(this).addClass(&#39;hover&#39;);
                }, function () {
                    $(this).removeClass(&#39;hover checkedHover&#39;);
                });
    
                //bind custom event, trigger it, bind click,focus,blur events
                wrapperDiv.bind(&#39;updateState&#39;, function () {
                    if ($(this)[0].children[1].checked) {
                        allInputs.each(function () {
                            var curDiv = $(&#39;div &gt; label[for=&#39; + $(this).attr(&#39;id&#39;) + &#39;]&#39;).parent();
                            curDiv.removeClass(&#39;custom-radio-checked&#39;);
                            curDiv.addClass(&#39;custom-radio&#39;);
                        });
                        $(this).toggleClass(&#39;custom-radio custom-radio-checked&#39;);
                    }
                    else {
                        $(this).removeClass(&#39;custom-radio-checked checkedHover checkedFocus&#39;);
                    }
    
                })
                .trigger(&#39;updateState&#39;)
                .click(function () { console.log(&#39;click&#39;); })
                .focus(function () {
                    label.addClass(&#39;focus&#39;);
                }).blur(function () {
                    label.removeClass(&#39;focus checkedFocus&#39;);
                });
            }); 
           });
       &lt;/script&gt;

Is there any solution for this behaviour?

jQuery Click fires twice when clicking on label

I read SO about another user encountering similar [error][1], but this error is in different case.

I received this message when I added a View Controller initially:

    Unbalanced calls to begin/end appearance transitions for 
    &lt;UITabBarController: 0x197870&gt;

The structure of the app is as follow:

I got a 5-tab TabBarController linked to 5 View Controllers. In the initial showing tab, I call out a new View Controller to overlay as an introduction of the app.

I use this code to call the introduction view controller:

    IntroVC *vc = [[IntroVC alloc] init];
    [self presentModalViewController:vc animated:YES];
    [vc release]; 

After this `IntroVC` view controller shows up, the above error shows. 

p.s. I am using xCode 4.2 &amp; iOS 5.0 SDK, developing iOS 4.3 app.


  [1]: https://stackoverflow.com/questions/6809593/unbalanced-calls-to-begin-end-appearance-transitions-for-firstviewcontroller-0

Unbalanced calls to begin/end appearance transitions for &lt;UITabBarController: 0x197870&gt;

How can I check whether a C# variable is an empty string `&quot;&quot;` or null?

I am looking for the simplest way to do this check. I have a variable that can be equal to `&quot;&quot;` or null. Is there a single function that can check if it&#39;s not `&quot;&quot;` or null?

How can I check whether a string variable is empty or null in C#?

<p>How can I check whether a C# variable is an empty string <code>""</code> or null?</p>
<p>I am looking for the simplest way to do this check. I have a variable that can be equal to <code>""</code> or null. Is there a single function that can check if it's not <code>""</code> or null?</p>


Am I right in thinking this is the correct use of a Concurrent Dictionary

    private ConcurrentDictionary&lt;int,long&gt; myDic = new ConcurrentDictionary&lt;int,long&gt;();
    
    //Main thread at program startup
    
    for(int i = 0; i &lt; 4; i++)
    {
      myDic.Add(i, 0);
    }
    
    //Separate threads use this to update a value
    
    myDic[InputID] = newLongValue;

I have no locks etc and am just updating the value in the dictionary even though multiple threads might be trying to do the same.

Concurrent Dictionary Correct Usage

Does C# have a *not* `Conditional` (`!Conditional`, `NotConditional`, `Conditional(!)`) attribute?


----------


i know C# has a [`Conditional` attribute][1]:

    [Conditional(&quot;ShowDebugString&quot;)]
    public static void ShowDebugString(string s)
    {
       ...
    }

which is equivalent&lt;sup&gt;1&lt;/sup&gt; to:

    public static void ShowDebugString(string s)
    {
    #if ShowDebugString
       ...
    #endif
    }

But in this case i want the *inverse* behavior (you have to specifically *opt out*):


    public static void ShowDebugString(string s)
    {
    #if !RemoveSDS
       ...
    #endif
    }

Which leads me to try:


    [!Conditional(&quot;RemoveSDS&quot;)]
    public static void ShowDebugString(string s)
    {
       ...
    }

which doesn&#39;t compile. And:


    [Conditional(&quot;!RemoveSDS&quot;)]
    public static void ShowDebugString(string s)
    {
       ...
    }

which doesn&#39;t compile. And:


    [NotConditional(&quot;RemoveSDS&quot;)]
    public static void ShowDebugString(string s)
    {
       ...
    }

which doesn&#39;t compile because it&#39;s only wishful thinking.

&lt;sup&gt;1&lt;/sup&gt; [Not true, but true enough. Don&#39;t make me bring back the Nitpicker&#39;s Corner.][2] &lt;sup&gt;[&#128343;][3]&lt;/sup&gt;


  [1]: https://msdn.microsoft.com/en-us/library/system.diagnostics.conditionalattribute
  [2]: http://blogs.msdn.com/b/oldnewthing/archive/2011/11/07/10234436.aspx
  [3]: https://web.archive.org/web/20111110161740/http://blogs.msdn.com/b/oldnewthing/archive/2011/11/07/10234436.aspx

C# !Conditional attribute?

What is the difference between `.Select()` and `.Where()` in Entity Framework?
Eg 

    return ContextSet().Select(x=&gt; x.FirstName == &quot;John&quot;)

vs

    ContextSet().Where(x=&gt; x.FirstName == &quot;John&quot;)

When should I use `.Select` vs `.Where`?

Difference between Select and Where in Entity Framework

I am creating a small helper function to return a `DataTable`. I would like to work across all providers that `ADO.Net` supports, so I thought about making everything use `IDbCommand` or `DbCommand` where possible.

I have reached a stumbling block with the following code:

        private static DataTable QueryImpl(ref IDbConnection conn, String SqlToExecute, CommandType CommandType, Array Parameters)
        {
            SetupConnection(ref conn);
            // set the capacity to 20 so the first 20 allocations are quicker...
            DataTable dt = new DataTable();
            using (IDbCommand cmd = conn.CreateCommand())
            {
                cmd.CommandText = SqlToExecute;
                cmd.CommandType = CommandType;
                if (Parameters != null &amp;&amp; Parameters.Length &gt; 0)
                {
                    for (Int32 i = 0; i &lt; Parameters.Length; i++)
                    {
                        cmd.Parameters.Add(Parameters.GetValue(i));
                    }
                }
                dt.Load(cmd.ExecuteReader(), LoadOption.OverwriteChanges);
            }
            return dt;
        }

When this code is executed, I receive an `InvalidCastException` which states the following:

&gt; The SqlParameterCollection only accepts non-null SqlParameter type objects, not String objects.

The code falls over on the line:

    cmd.Parameters.Add(Parameters.GetValue(i));

Any ideas? 

Any improvements to the above code is appreciated.

----

Actual solution: 


        private static readonly Regex regParameters = new Regex(@&quot;@\w+&quot;, RegexOptions.Compiled);
        private static DataTable QueryImpl(ref DbConnection conn, String SqlToExecute, CommandType CommandType, Object[] Parameters)
        {
            SetupConnection(ref conn);
            DataTable dt = new DataTable();
            using (DbCommand cmd = conn.CreateCommand())
            {
                cmd.CommandText = SqlToExecute;
                cmd.CommandType = CommandType;
                if (Parameters != null &amp;&amp; Parameters.Length &gt; 0)
                {
                    MatchCollection cmdParams = regParameters.Matches(cmd.CommandText);
                    List&lt;String&gt; param = new List&lt;String&gt;();
                    foreach (var el in cmdParams)
                    {
                        if (!param.Contains(el.ToString()))
                        {
                            param.Add(el.ToString());
                        }
                    }
                    Int32 i = 0;
                    IDbDataParameter dp;
                    foreach (String el in param)
                    {
                        dp = cmd.CreateParameter();
                        dp.ParameterName = el;
                        dp.Value = Parameters[i++];
                        cmd.Parameters.Add(dp);
                    }
                }
                dt.Load(cmd.ExecuteReader(), LoadOption.OverwriteChanges);
            }
            return dt;
        } 

Thanks for ideas/links etc. :)

Adding parameters to IDbCommand

In my code I need to use an `IEnumerable&lt;&gt;` several times, resulting in the ReSharper error of &quot;Possible multiple enumeration of `IEnumerable`&quot;.

Sample code:

    public List&lt;object&gt; Foo(IEnumerable&lt;object&gt; objects)
    {
        if (objects == null || !objects.Any())
            throw new ArgumentException();
            
        var firstObject = objects.First();
        var list = DoSomeThing(firstObject);        
        var secondList = DoSomeThingElse(objects);
        list.AddRange(secondList);
        
        return list;
    }

 - I can change the `objects` parameter to be `List` and then avoid the possible multiple enumeration but then I don&#39;t get the highest object that I can handle.  
 - Another thing that I can do is to convert the `IEnumerable` to `List` at the beginning of the method:   

--- 
     public List&lt;object&gt; Foo(IEnumerable&lt;object&gt; objects)
     {
        var objectList = objects.ToList();
        // ...
     }

But this is just **awkward**.

What would you do in this scenario?

Handling warning for possible multiple enumeration of IEnumerable

I want to replace a substring (e.g. `@&quot;replace&quot;`) of an `NSAttributedString` with another `NSAttributedString`.

I am looking for an equivalent method to `NSString`&#39;s [`stringByReplacingOccurrencesOfString:withString:`](https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSString_Class/Reference/NSString.html#//apple_ref/doc/uid/20000154-SW6) for `NSAttributedString`.

Replace substring of NSAttributedString with another NSAttributedString

I need a method that can tell me if a String has non alphanumeric characters.

For example if the String is &quot;abcdef?&quot; or &quot;abcdef&#224;&quot;, the method must return true.


How to determine if a String has non-alphanumeric characters?

Is there a PHP function that can do that?

I&#39;m using `strpos` to get the position of a substring and I want to insert a `string` after that position.

Insert string at specified position

How do you convert an `int` (integer) to a string? I&#39;m trying to make a function that converts the data of a `struct` into a string to save it in a file.

How to convert an int to string in C?

I have a string variable with content:

    varMessage =   
                &quot;hi/thsid/sdfhsjdf/dfjsd/sdjfsdn\n&quot;
    
    
                &quot;/my/name/is/balaji.so\n&quot;
                &quot;call::myFunction(int const&amp;)\n&quot;
                &quot;void::secondFunction(char const&amp;)\n&quot;
                 .
                 .
                 .
                &quot;this/is/last/line/liobrary.so&quot;

In the string I have to find a sub-string:

    &quot;hi/thsid/sdfhsjdf/dfjsd/sdjfsdn\n&quot;
    
    &quot;/my/name/is/balaji.so\n&quot;
    &quot;call::myFunction(int const&amp;)\n&quot;

How can I find it? I need to determine whether the sub-string is present or not.

How to check whether a string contains a substring in Ruby

 I know generally empty List is more prefer than NULL. But I am going to return NULL, for mainly two reasons

 1. I have to check and handle null values explicitly, avoiding bugs and attacks.
 2. It is easy to perform `??` operation afterwards to get a return value.

For strings, we have IsNullOrEmpty. Is there anything **from C# itself** doing the same thing for List or IEnumerable?

Does C# have IsNullOrEmpty for List/IEnumerable?

I usually use something like this for various reasons throughout an application:

    if (String.IsNullOrEmpty(strFoo))
    {
         FooTextBox.Text = &quot;0&quot;;
    }
    else
    {
         FooTextBox.Text = strFoo;
    }

If I&#39;m going to be using it a lot I will create a method that returns the desired string. For example:

    public string NonBlankValueOf(string strTestString)
    {
        if (String.IsNullOrEmpty(strTestString))
            return &quot;0&quot;;
        else
            return strTestString;
    }

and use it like: 

    FooTextBox.Text = NonBlankValueOf(strFoo);

I always wondered if there was something that was part of C# that would do this for me. Something that could be called like: 

    FooTextBox.Text = String.IsNullOrEmpty(strFoo,&quot;0&quot;)

the second parameter being the returned value if `String.IsNullOrEmpty(strFoo) == true` 


If not does anyone have any better approaches they use?

One liner for If string is not null or empty else

What are differences between these commands in C#

    string text= &quot;  &quot;;
    1-string.IsNullOrEmpty(text.Trim())

    2-string.IsNullOrWhiteSpace(text)

Difference between IsNullOrEmpty and IsNullOrWhiteSpace in C#

I have a generic list object. I need to check if the list is empty. 

How do I check if a `List&lt;T&gt;` is empty in C#?



Content Type	Original Author	Original Content on Stackoverflow
Question	Samantha J T Star	View Question on Stackoverflow
Solution 1 - C#	oopbase	View Answer on Stackoverflow
Solution 2 - C#	madd0	View Answer on Stackoverflow
Solution 3 - C#	jk.	View Answer on Stackoverflow
Solution 4 - C#	yrk	View Answer on Stackoverflow
Solution 5 - C#	cristobalito	View Answer on Stackoverflow
Solution 6 - C#	Asker	View Answer on Stackoverflow

How can I check whether a string variable is empty or null in C#?

C# Problem Overview

C# Solutions

Solution 1 - C#

Solution 2 - C#

Solution 3 - C#

Solution 4 - C#

Solution 5 - C#

Solution 6 - C#

Unbalanced calls to begin/end appearance transitions for <UITabBarController: 0x197870>

jQuery Click fires twice when clicking on label

Attributions