Develop Reference

C# NullReferenceException but nothing is null

I have a C# class with a field and a property that looks like this.
public static class Config {
// ...
private static string admin_email;
public static string AdminEmail {
get {
if (admin_email == null) {
admin_email = config_xml.Element("admin_email").Value;
// ^ The exception is thrown here.
}
return admin_email;
}
}
}
In the above code, config_xml is an XElement which contains a child element that looks like
<admin_email>myemail#example.com</admin_email>
However, when I try to access this property, I get a NullReferenceException even though the debugger shows that nothing is null.
I checked the debugger, and watching config_xml.Element("admin_email").Value shows the email, as expected.
The weird part is that when I put a breakpoint on that line and step in one step at a time there is no exception thrown.
I have tried with and without enabling the option Just My Code.
In case this helps, I try to access the property on a line like this (from a different project)
message.From = new MailAddress(Config.AdminEmail);
Edit
After changing the code to this, I realised that c was still null.
get {
if (admin_email == null) {
XElement c = config_xml;
XElement e = c.Element("admin_email");
// ^ Exception is now thrown here
string v = e.Value;
admin_email = v;
}
return admin_email;
}

Thank you David, asawyer, and Lasse V. Karlsen for helping me realise my mistake. I changed my code to this, and now it works.
admin_email = new Email(ConfigXml.Element("admin_email").Value;
I was using a similar technique for config_xml and ConfigXml, so I would only load the XML into the field config_xml if it was ever needed, and I forgot to access it with the property ConfigXml (which did the loading) instead of the field config_xml (which was null until I used the property).
I don't know why it was working with a breakpoint, maybe when I watched the property it assigned it? I don't know.

InstallerSetup.cs pass installation parameters in from1.cs

I have properly overwrite commit in InstallerSetup.cs I do not wish to write the user entered value to app.config but rather I want to pass the string Context.Parameters["TESTPARAMETER"]; to another class in form1.cs on load function. I tried string test = InstallerSetup.Context.Parameters["TESTPARAMETER"];
but getting InstallerSetup.Context is null. Please Help.
InstallerSetup.cs
public static string SQLSERVERNAME = "";
public static string HMSTENANTDB;
public static string SQLLOGIN;
public static string SQLPASSWORD;
public override void Commit(IDictionary savedState)
{
base.Commit(savedState);
try
{
SQLSERVERNAME = Context.Parameters["SQLSERVERNAME"];
HMSTENANTDB = Context.Parameters["HMSTENANTDB"];
SQLLOGIN = Context.Parameters["SQLLOGIN"];
SQLPASSWORD = Context.Parameters["SQLPASSWORD"];
}
catch (Exception e)
{
MessageBox.Show("Failed to update the application configuration file : " + e.Message);
base.Rollback(savedState);
}
}
from1.cs
InstallerSetup InsSetup = new InstallerSetup();
string Vsqlserver = InsSetup.Installers.Count.ToString();
string Vtenant = "";
if (InsSetup.Context != null)
{
Vtenant = InsSetup.Context.Parameters["HMSTENANTDB"];
}
else
{
Vtenant = "context is null";
}

As far as I can tell, the issue is that the property values are not being passed into the custom action. That would be the most obvious explanation. A commentfrom the poster says:
"passed those parameters to the custom action...................................... SQLSERVERNAME = Context.Parameters["SQLSERVERNAME"];
etc...
//................there is only these 4 lines in my custom actions"
which is essentially repeating the code that was previously posted.
This is NOT passing the values into the custom action. This is retrieving values which must already have been passed into the custom action.
Assuming that the custom action has been correctly added to (typically) the install nod of the custom action, and also assuming that the property names are in a TextBoxes dialog in the install, the values must be passed in to the custom action via the CustomActionData settings. To use one example, the CustomActionData setting must be something like:
/SQLSERVERNAME=[SQLSERVERNAME]
or /SQLSERVERNAME=[EDITA1] if EDIOTA1 is being used because that's the default property name.
However there is no reference to the TextBoxes (or any other) install dialog in the original question, so it's not really clear where the value of (say) SQLSERVERNAME is supposed to come from. It may be passed in on the msiexec command line, for example.

How to shim property being set on a 3rd party external dll

I am working on writing a unit test for the following function..
public virtual FacadeClass InitNewAMSObject()
{
FacadeClass output = null;
if (ClassMapInfo != null)
{
// Override the metadata caching option
// sets property in external dll
Avectra.netForum.Common.Config.CacheMetaData = false;
if (!String.IsNullOrEmpty(ClassMapInfo.AMSClassName))
{
output = DataUtils.InstantiateFacadeObject(ClassMapInfo.AMSClassName);
}
}
else
{
throw new System.ApplicationException("Need to add the attribute");
}
return output;
}
I cannot get past the line with the comment "sets property in external dll". My shim never seems to 'make it over' to the function being tested. It always throws an error, and its actually trying to use the dll instead of my shim. It may look like i'm setting a property to false only, but the dll uses the property like a method in it's Setter. The .Config is always in an errored state because its constructors (in the dll) are attempting to set up database connections. I expect it to be in at least a null state, and also have the .Fakes. in the class name. I just want to skip over it because I do not write this dll, its 3rd party.
I've researched for a day now and cannot find an example anywhere of how to shim a property that is set on a referenced dll.
Here is my current test for what its worth
[TestMethod]
public void InitNewAMSObjectTEST()
{
using (ShimsContext.Create())
{
Address amsc = new Address();
bool test = true;
ShimConfig.CacheMetaDataGet = () => test;
ShimConfig.CacheMetaDataSetBoolean = value => test = value;
amsc.InitNewAMSObject();
}
}

How to get the value of a property of a class in a non executing assembly through reflection

I'm having trouble while getting the value of the text property in a non-executing assembly; I read an assembly from disk via reflection, then i get all classes in the assembly to search for the Text property in a windows form class which is initialized by win forms designer. So far i have the following code:
static void Main(string[] args)
{
Assembly asm = Assembly.LoadFrom(Path.Combine(path, "Assembly.exe"));
PropertyInfo[] props;
foreach (Type t in asm.GetTypes())
{
var value = t.GetProperty("Text").GetValue(/*Not sure what to put here*/)
}
}
And this is how the designer generated the form
Me.AutoScaleMode = System.Windows.Forms.AutoScaleMode.None
Me.BackColor = System.Drawing.Color.FromArgb(CType(CType(0, Byte), Integer), CType(CType(128, Byte), Integer), CType(CType(128, Byte), Integer))
Me.ClientSize = New System.Drawing.Size(234, 181)
Me.Cursor = System.Windows.Forms.Cursors.Default
Me.Font = New System.Drawing.Font("Arial", 8.25!, System.Drawing.FontStyle.Bold, System.Drawing.GraphicsUnit.Point, CType(0, Byte))
Me.ForeColor = System.Drawing.SystemColors.WindowText
Me.FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedDialog
Me.Location = New System.Drawing.Point(581, 222)
Me.MaximizeBox = False
Me.MinimizeBox = False
Me.Name = "winform"
Me.RightToLeft = System.Windows.Forms.RightToLeft.No
Me.StartPosition = System.Windows.Forms.FormStartPosition.Manual
Me.Text = "Title"
Me.fraDías.ResumeLayout(False)
Me.ResumeLayout(False)
Keep in mind that the assembly is on disk and non-executing and that I want to retrieve the value of the Text property of every winform (I guess it should be somewhere hardcoded in the assembly since it was generated by the winforms designer)
Please tell me if this is possible, thanks!

Your requirements are contradictory, when you load an aseembly via reflection, and instantiate an object or try to get a property value, what happens is that some code begins to run, there is no way around that.
Remember that properties are just "syntax sugar" for a pair of methods, the getter and setter. Their current value is nothing but the value returned by the getter method, and when you change its value, you're in fact calling its setter method. So, to retrieve property values, you must make some code to run, even if it's a trivial get method.
I think maybe your confusion comes from the fact that you're using a designer to create the form. Particularly with the WinForms designer (WPF for instance is substantially different), all it does is to autogenerate some code for you. Setting properties, placing and moving controls around, what's happening under the hood is that it writes code that replicate your actions at runtime, specifically, it codes the InitializeComponent method. The real property value is set when the constructor is called (that in turn calls InitializeComponent), and then you may read/change using many properties.
What you would need to read those designer attributes is that those were hardcoded in some form of metadata, so that it's simply read as data and not as the result of code execution. That's not the case with WinForms, as it "saves" the form as code.

You cannot read a property of a class that has not been instantiated! The parameter you are missing is an instance of your type.
You must create an instance of the type with object o = Activator.CreateInstance(type); before accessing its members (unless they are static).
Your problem is related to how add-ins (plug-ins) can be loaded at runtime.
Here is how I made an Add-In Loader. Below, I will explain how you can adapt it to your problem. Add-Ins have to implement the IAddIn interface in my example. You are totally free in the definition of IAddIn. You could define it like this:
public interface IAddIn
{
bool OnLoad();
string Version { get; set; }
string Text { get; set; }
}
This allows you to access members without reflection.
public class AddInLoader
{
// Loads all non abstract types implementing IAddIn in all DLLs found in a folder.
public IList<IAddIn> Load(string folder)
{
var addIns = new List<IAddIn>();
string[] files = Directory.GetFiles(folder, "*.dll");
foreach (string file in files) {
addIns.AddRange(LoadFromAssembly(file));
}
return addIns;
}
// Loads all non abstract types implementing IAddIn found in a file.
private static IEnumerable<IAddIn> LoadFromAssembly(string fileName)
{
Assembly asm = Assembly.LoadFrom(fileName);
string addInInterfaceName = typeof(IAddIn).FullName;
foreach (Type type in asm.GetExportedTypes()) {
Type interfaceType = type.GetInterface(addInInterfaceName);
if (interfaceType != null &&
(type.Attributes & TypeAttributes.Abstract) != TypeAttributes.Abstract){
IAddIn addIn = (IAddIn)Activator.CreateInstance(type);
addIn.Version = asm.GetName().Version.ToString();
yield return addIn;
}
}
}
}
Now you can load and access the add-ins like this:
var loader = new AddInLoader();
IList<IAddIn> addIns = loader.Load(folderPath);
foreach (IAddIn addIn in addIns) {
if (addIn.OnLoad()) {
Console.WriteLine("Version = {0}, Text = {1}", addIn.Version, addIn.Text);
}
}
Reading the titles of Forms at runtime:
You can easily adapt this example. Instead of searching for types implementing an interface, search for types deriving from System.Windows.Forms.Form.
private static IEnumerable<Form> LoadFormsFromAssembly(string fileName)
{
Assembly asm = Assembly.LoadFrom(fileName);
foreach (Type type in asm.GetExportedTypes()) {
if (typeof(Form).IsAssignableFrom(type) &&
(type.Attributes & TypeAttributes.Abstract) != TypeAttributes.Abstract) {
Form form = (Form)Activator.CreateInstance(type);
yield return form;
}
}
}
Now you can get the texts of the forms like this:
var forms = LoadFormsFromAssembly(path);
foreach (Form frm in forms) {
Console.WriteLine(frm.Text);
}
Note: You must instantiate the forms, however you do not need to open (show) them. The code works only if the forms have a default constructor, i.e. a constructor without parameters.

You need an instance object for that type to get the value of a property.
It looks like you just want to check if a type has a "Text" property or not. You can to it by checking
bool hasTextProperty = t.GetProperty("Text") !=null;

Is it possible to execute C# code represented as string?

On my form I have a button click
private void button1_Click(object sender, EventArgs e)
{
do something
}
How on the click would I load my do something from a text file, for example my text file looks like this:
MessageBox.Show("hello");
label1.Text = "Hello";
on click it does everything in my text file, if possible.

Here is a very simple example, just to prove this is possible. Basically, you use CodeDomProvider to compile source at runtime, then execute using reflection.
var provider = CodeDomProvider.CreateProvider("C#");
string src=#"
namespace x
{
using System;
public class y
{
public void z()
{
Console.WriteLine(""hello world"");
}
}
}
";
var result = provider.CompileAssemblyFromSource(new CompilerParameters(), src);
if (result.Errors.Count == 0)
{
var type = result.CompiledAssembly.GetType("x.y");
var instance = Activator.CreateInstance(type);
type.GetMethod("z").Invoke(instance, null);
}
Edit
As #Agat points out, the OP seems to require a sort of scripting framework (it makes use of label1, a property of the current object), whereas my answer above obviously does not provide that. The best I can think of is a limited solution, which would be to require dependencies to be specified explicitly as parameters in the "script". Eg, write the scripted code like this:
string src = #"
namespace x
{
using System.Windows;
public class y
{
public void z(Label label1)
{
MessageBox.Show(""hello"");
label1.Text = ""Hello"";
}
}
}
";
Now you can have the caller examine the parameters, and pass them in from the current context, again using reflection:
var result = provider.CompileAssemblyFromSource(new CompilerParameters(), src);
if (result.Errors.Count == 0)
{
var type = result.CompiledAssembly.GetType("x.y");
var instance = Activator.CreateInstance(type);
var method = type.GetMethod("z");
var args = new List<object>();
// assume any parameters are properties/fields of the current object
foreach (var p in method.GetParameters())
{
var prop = this.GetType().GetProperty(p.Name);
var field = this.GetType().GetField(p.Name);
if (prop != null)
args.Add(prop.GetValue(this, null));
else if (field != null);
args.Add(field.GetValue(this));
else
throw new InvalidOperationException("Parameter " + p.Name + " is not found");
}
method.Invoke(instance, args.ToArray());
}

Like the other answers have stated, it isn't an easy thing to implement and can possibly be done through reflection depending on how advanced your scripts are.
But no one #BrankoDimitrijevic mentioned Roslyn and it is a great tool. http://msdn.microsoft.com/en-us/vstudio/roslyn.aspx
It hasn't been updated in quite awhile (Sept.2012) and doesn't have all of the features of C# implemented, however, it did have a lot of it implemented when I played around with this release.
By adding your assembly as a reference to the scripting session, you're able to gain access to all of your assembly's types and script against them. It also supports return values so you can return any data that a scripted method generates.
You can find what isn't implemented here.
Below is a quick and dirty example of Roslyn that I just wrote and tested. Should work right out of box after installing Roslyn from NuGet. The small bloat at the initialization of the script engine can easily be wrapped up in a helper class or method.
The key is passing in a HostObject. It can be anything. Once you do, your script will have full access to the properties. Notice that you just call the properties and not the host object in the script.
Basically, your host object will contain properties of the data you need for your script. Don't necessarily think of your host object as just a single data object, but rather a configuration.
public class MyHostObject
{
public string Value1 { get; set; }
public string Value2 { get; set; }
}
public class RoslynTest
{
public void Test()
{
var myHostObject = new MyHostObject
{
Value1 = "Testing Value 1",
Value2 = "This is Value 2"
};
var engine = new ScriptEngine();
var session = engine.CreateSession(myHostObject);
session.AddReference(myHostObject.GetType().Assembly.Location);
session.AddReference("System");
session.AddReference("System.Core");
session.ImportNamespace("System");
// "Execute" our method so we can call it.
session.Execute("public string UpdateHostObject() { Value1 = \"V1\"; Value2 = \"V2\"; return Value1 + Value2;}");
var s = session.Execute<string>("UpdateHostObject()");
//s will return "V1V2" and your instance of myHostObject was also changed.
}
}

No. You can not.
At least in any simple way.
The thing you want is something like eval('do something') from javascript.
That's not possible to do with C#. C# is a language which needs compilation before execution unlike javascript (for instance).
The only way to implement that is to build your own (pretty complicated as for beginner) parser and execute it in such way.
UPDATED:
Actually, as JDB fairly noticed, that's really not the only way. I love programming! There are so many ways to make a freakky (or even sometimes that really can be necessary for some custom interesting tasks (or even learning)!) code. he he
Another approach I've got in my mind is building some .cs file, then compiling it on-the-fly and working with it as some assembly or some other module. Right.