I want to check that a property on an array which is itself a child object is not null.
So i have
if (Parent.Child != null && Parent.Child[0] != null && Parent.Child[0].name != null)
var myName = Parent.Child[0].name
This seems like a very long winded way to get to the child[0].name whilst avoiding null reference exceptions. I am also getting index out of range errors. Is there a better way?
If you're getting IndexOutOfRangeException errors, that suggests that Parent.Child could be empty. So really you want:
if (Parent.Child != null && Parent.Child.Count > 0 && Parent.Child[0] != null &&
Parent.Child[0].name != null)
{
...
}
There's nothing that would simplify this very much, although you could write a version of LINQ's FirstOrDefault method which even coped with the source being null:
public static T NullSafeFirstOrDefault(this IEnumerable<T> source)
{
return source == null ? default(T) : source.FirstOrDefault();
}
Then:
var firstChild = Parent.Child.NullSafeFirstOrDefault();
if (firstChild != null && firstChild.name != null)
{
...
}
Your code appears OK apart from missing a test for the array being empty and is the correct defensive programming. You should extract this into a method to make it's intention clearer and your code here cleaner:
if (Parent.HasChild())
{
var myName = Parent.Child[0].name;
}
public bool HasChild()
{
return this.Child != null && this.Child.Count > 0 &&
this.Child[0] != null && this.Child[0].name != null;
}
The only other way would be to wrap the code in a try/catch block:
try
{
var myName = Parent.Child[0].name;
...
}
catch
{
}
However, this is bad programming practice as:
You are using exceptions to control program flow.
You are hiding other potentially serious errors.
try
var Names = new List<string>();
if(Parent.Child != null && Parent.Child.Count() > 0){
foreach(var item in Parent.Child) Names.Add(item.name)
}
var ParentChild= Parent.Child[0] ;
if (Parent.Child != null && ParentChild != null &&ParentChild.name != null)
var myName = ParentChild.name
Maybe simple try/catch will help?
var myName;
try
{
myName = Parent.Child[0].name;
}
catch (NullReferenceException)
{ myName = null; }
Related
I have a ConcurrentDictionary of Attributes for products. These attributes have the product ID and values for the names of the attribute and any options the attribute has. I have this ConcurrentDictionary because I have threads that are created to handle each attribute in the dictionary by attribute name.
if (knownAttribute.AttributeType.Value.Equals("Product Specification"))
{
Console.WriteLine("Started a thread for: " + knownAttribute.AttributeTypeId + ", " + knownAttribute.Value);
while (true)
{
/* if (AS400SpecificationAttributes.IsEmpty && knownSpecificationBag.IsEmpty && gatherRowsTasks.All(x => x.IsCompleted))
break;*/
AS400SpecificationAttribute AS400SpecificationAttributeWork = null;
AS400SpecificationAttributeWork = knownSpecificationBag.Keys.FirstOrDefault(x => x.AttributeName == knownAttribute.Value);
if (AS400SpecificationAttributeWork != null)
{
var product = ctx.Products.FirstOrDefault(x => x.ProductNumber == AS400SpecificationAttributeWork.ProductNumber);
if (product == null)
continue;
var productAttribute = new ProductAttribute();
productAttribute.Attribute = knownAttribute;
if (AS400SpecificationAttributeWork.AttributeValue != null)
{
var knownAttributeOption = ctx.AttributeOptions.FirstOrDefault(x => x.Attribute.Equals(knownAttribute) && x.Value.Equals(AS400SpecificationAttributeWork.AttributeValue));
if (knownAttributeOption == null)
{
knownAttributeOption = new AttributeOption();
knownAttributeOption.Value = AS400SpecificationAttributeWork.AttributeValue;
knownAttributeOption.Attribute = knownAttribute;
ctx.AttributeOptions.InsertOnSubmit(knownAttributeOption);
ctx.SubmitChanges();
}
productAttribute.AttributeOption = knownAttributeOption;
productAttribute.AttributeOptionId = knownAttributeOption.Id;
}
product.ProductAttributes.Add(productAttribute);
ctx.SubmitChanges();
string tmpstr = null;
if (!knownSpecificationBag.TryRemove(AS400SpecificationAttributeWork, out tmpstr))
Thread.Sleep(50);
}
else
{
if (tryCounter < 5)
{
tryCounter++;
Thread.Sleep(1000);
Console.WriteLine("Thread waiting for work: Product Specification:" + knownAttribute.Value);
continue;
}
else
{
int outVal;
threadTracker.TryRemove("Product Specification:" + knownAttribute.Value, out outVal);
Console.WriteLine("Closing Thread: Product Specification:" + knownAttribute.Value);
break;
}
}
Thread.Sleep(50);
}
It seems like the following Attribute element refuses to be removed.
I don't understand why. If i put it in a while(!dic.tryRemove(ele)) it will forever be stuck and never move from there.
There may be an error somewhere within the thread but I have no idea why.
This statement
if (!knownSpecificationBag.TryRemove(AS400SpecificationAttributeWork, out tmpstr))
will always return true or false. It won't block. That's the behavior of ConcurrentDictionary. It will return false if the key is not in the dictionary.
If you're looping while that method returns false and it's stuck, that means that the item isn't in the dictionary when the loop begins. Either it either was never in the dictionary or that another thread already removed it.
Is your intention to loop until the item is not in the dictionary?
You could try this:
if (!knownSpecificationBag.TryRemove(AS400SpecificationAttributeWork, out tmpstr)
&& !knownSpecificationBag.ContainsKey(AS400SpecificationAttributeWork))
Implement proper equals and gethashcode when using TryRemove
public override int GetHashCode()
{
return new { this.name, this.value, this.group, this.productNumber }.GetHashCode();
}
public bool Equals(AS400SpecificationAttribute other)
{
if (other == null)
return false;
return (this.ProductNumber.Equals(other.productNumber) && ((this.group != null && this.group.Equals(other.AttributeGroup)) || (this.group == null && other.AttributeGroup == null)) && ((this.name!= null && this.name.Equals(other.AttributeName)) || (this.name == null && other.AttributeName == null)) && ((this.value != null && this.value.ToUpper().Equals(other.AttributeValue.ToUpper())) || (this.value == null && other.AttributeValue == null)));
}
I have a object with type:
dynamic {System.DBNull}
I want to check it:
if (myObject!= null || myObject!= DBNull.Value)
{
MessageBox.Show("Oh hi");
}
But the MessageBox always appears. Whats wrong, is it another type?
This expression is always true
myObject != null || myObject != DBNull.Value
because myObject cannot be null and DBNull.Value at the same time. Replace || with && to fix.
Try this code
if(myObject != DBNull.Value)
{
MessageBox.Show("Oh hi");
}
or
if(myObject != null && myObject != DBNull.Value)
{
MessageBox.Show("Oh hi");
}
There is also a function for checking for DBNull:
if(myObject != null && !Convert.IsDBNull(myObject))
{
MessageBox.Show("Oh hi");
}
I have string with empty space("________")
string MyNote= Convert.ToString(Session["MyNote"]);
if(MyNote!=null || MyNote != "")
{
}
MyNote != "" does not work if string has more space so
How can I check my string is "" or null by using linq in C#?
String.IsNullOrWhiteSpace is the method you're looking for.
Indicates whether a specified string is null, empty, or consists only of white-space characters.
Alternatively, using your idea:
if(MyNote!=null && MyNote.Trim() != "")
{
}
or
if(MyNote!=null && MyNote.Trim().Length == 0)
{
}
if(MyNote!=null || MyNote.Length > 0) //or you may want to set different value than 0
{
}
This works for me:
string MyNote = Session["MyNote"] == null ? String.Empty : Session["MyNote"].ToString();
I want to write a check for some conditions without having to use try/catch and I want to avoid the possibilities of getting Index Out of Range errors
if (array.Element[0].Object.Length > 0 || array.Element[1].Object.Length > 0) //making sure there's at least one Object array that has values
{
if (array.Element[0].Object[0].Item.Length != 0 || array.Element[1].Object[0].Item.Length != 0) //this is where I check that at least one of the Items (strings) is not empty
{
// execute code here
}
}
So the problem I am facing is that in the second check I need to see whether I have one Item that is not empty. However, If I don't have Element[1], I get the Index Out of Range exception. The problem is that there could be 2 Elements and one(or both) of them may have empty Object arrays. The code will have to be executed only if one of thos Item strings is not empty.
Hopefully, I explained it well. How do I go about avoiding getting that exception under any condition?
Alright, you need some better null checking and some more cautious code here.
if (array.Element[0].Object.Length > 0 || array.Element[1].Object.Length > 0) //making sure there's at least one Object array that has values
{
if (array.Element[0].Object[0].Item.Length != 0 || array.Element[1].Object[0].Item.Length != 0) //this is where I check that at least one of the Items (strings) is not empty
{
// execute code here
}
}
is just unacceptable.
First, let's null check
if (array != null)
{
if (array.Element != null)
for simplicity, you could use &&
if (array != null && array.Element != null)
then, inside that if, we use a for loop (since you're stuck on arrays) and null check it
for (int i = 0; i < array.Element; ++i)
{
if (array.Element[i] != null && array.Element[i].Object != null)
{
then, since you have nested arrays, we loop again. This is called a nested loop, and it's generally bad practice, I'll show you why it works in a second.
for (int o = 0; o < array.Element[i].Object.length; ++o)
{
if (array.Element[i].Object[o] != null && !string.IsNullOrEmpty(array.Element[i].Object[o].Item))
{
Now, with all of that ugly nested loopyness, we've found out that your Item is not null.
On top of that, you have access to ALL of the potential values here, and can group them as you like. Here's how I would put the whole thing together for simplification.
List<string> arrayValues = new List<string>();
if (array != null && array.Element != null)
{
for (int i = 0; i < array.Element.length; ++i)
{
//bool found = false;
if (array.Element[i] != null && array.Element[i].Object != null)
{
for (int o = 0; o < array.Element[i].Object.length; ++o)
{
if (array.Element[i].Object[o] != null && !string.IsNullOrEmpty(array.Element[i].Object[o].Item))
{
arrayValues.Add(array.Element[i].Object[o].Item);
//if you want to drop out here, you put a boolean in the bottom loop and break and then break out of the bottom loop if true
//found = true;
//break;
}
}
}
//if (found)
// break;
}
}
if (arrayValues.Count > 0)
{
//do stuff with arrayValues
}
Could use a LINQ method ElementAtOrDefault(index)
so if the element is not found it will be null.
var currentElem = Elems.ElementAtOrDefault(i);
if(currentElem != null)
// do something
else
// do something
Could you do something like:
if(array.Element[0] != null || array.Element[1] != null){
//execute code
}
Your code is probably subject to refactor.
I assume it can work this way:
var obj = array.Element.FirstOrDefault(x => x.Object.Length > 0);
if (obj != null)
{
if (obj.Object[0].Item.Length != 0)
{
// do whatever is necessary
}
}
I think you can put your check in right before your first if Check.
if (array.Length > 1 && array.Element[0].Object.Length > 0 || array.Element[1].Object.Length > 0) //making sure there's at least one Object array that has values
{
if (array.Element[0].Object[0].Item.Length != 0 || array.Element[1].Object[0].Item.Length != 0) //this is where I check that at least one of the Items (strings) is not empty
{
// execute code here
}
}
This should just short-circuit out if your array doesn't have both Elements.
Place both tests together using the short-circuit && so that the second test doesn't occur if the first fails:
object element0 = array.Element[0].Object;
object element1 = array.Element[1].Object;
// Ensure at least one Object array has a non-empty value.
if ((element0.Length > 0 && !string.IsNullOrEmpty((string)element0.Object[0].Item))
|| (element1.Length > 0 && !string.IsNullOrEmpty((string)element1.Object[1].Item)))
{
// ...
}
I am presuming it is Object[1] causing the exception--you weren't clear on that. If it is Element[1] that causes the exception (or both), then you need to pre-test the length of the array:
if ((array.Element[0].Length != 0 && HasValue(array.Element[0].Object))
|| (array.Element[1].Length > 1 && HasValue(array.Element[1].Object)))
{
// ...
}
// <summary>
// Returns true if the specified string array contains a non-empty value at
// the specified index.
// </summary>
private bool HasValue(System.Array array, int index)
{
return array.Length > index &&
!string.IsNullOrEmpty((string)array.Object[index].Item);
}
for (long i = 0; i <= (output3.Length); i++)
{
output1.WriteByte(output3[i]); -----> index out of range exception correct it
output1.WriteByte(output3rx[i]);
}
What would be the best way to determine if an object equals number zero (0) or string.empty in C#?
EDIT: The object can equal any built-in System.Value type or reference type.
Source Code:
public void MyMethod(object input1, object input2)
{
bool result = false;
object compare = new object();
if(input != null && input2 != null)
{
if(input1 is IComparable && input2 is IComparable)
{
//do check for zero or string.empty
//if input1 equals to zero or string.empty
result = object.Equals(input2);
//if input1 not equals to zero or string.empty
result = object.Equals(input1) && object.Equals(input2); //yes not valid, but this is what I want to accomplish
}
}
}
Using Jonathan Holland code sample with a minor modification, here is the solution that worked:
static bool IsZeroOrEmpty(object o1)
{
bool Passed = false;
object ZeroValue = 0;
if(o1 != null)
{
if(o1.GetType().IsValueType)
{
Passed = (o1 as System.ValueType).Equals(Convert.ChangeType(ZeroValue, o1.GetType()))
}
else
{
if (o1.GetType() == typeof(String))
{
Passed = o1.Equals(String.Empty);
}
}
}
return Passed;
}
What's wrong with this?
public static bool IsZeroOrEmptyString(object obj)
{
if (obj == null)
return false;
else if (obj.Equals(0) || obj.Equals(""))
return true;
else
return false;
}
Michael, you need to provide a little bit more information here.
strings can be compared to null or string.Empty by using the method
string x = "Some String"
if( string.IsNullOrEmpty(string input) ) { ... }
int, decimals, doubles (and other numeric value-types) can be compared to 0 (zero) with a simple == test
int x = 0;
if(x == 0) { ... }
You can also have nullable value-types also by using the ? operator when you instantiate them. This allows you to set a value type as null.
int? x = null;
if( !x.HasValue ) { }
For any other object, a simple == null test will tell you if its null or not
object o = new object();
if( o != null ) { ... }
Hope that sheds some light on things.
Not quite sure the reasoning behind this, because .Equals is reference equality on reference types, and value equality on value types.
This seems to work, but I doubt its what you want:
static bool IsZeroOrEmpty(object o1)
{
if (o1 == null)
return false;
if (o1.GetType().IsValueType)
{
return (o1 as System.ValueType).Equals(0);
}
else
{
if (o1.GetType() == typeof(String))
{
return o1.Equals(String.Empty);
}
return o1.Equals(0);
}
}
Do you mean null or string.empty, if you're talking about strings?
if (String.IsNullOrEmpty(obj as string)) { ... do something }
Oisin
In the first case by testing if it is null. In the second case by testing if it is string.empty (you answered your own question).
I should add that an object can never be equal to 0. An object variable can have a null reference though (in reality that means the variable has the value of 0; there is no object in this case though)
obj => obj is int && (int)obj == 0 || obj is string && (string)obj == string.Empty