I have defined my buttons in the .xaml.
In the MainPage.xaml.cs I am trying to put them in an array.
myButtons[]={But_1,But_2,But_n....};
I get the following error.
A field initializer cannot reference the non-static field, method, or property 'NoteTrainer_.MainPage.But_1'
If i put that array in the MainPage() constructor I get no errors,but then I cannot access the array from my methods.
Kinda new to C# and Windows-Phone
Thanks for the help.
Well, to start with that declaration looks wrong. But for a second thing, the compiler is telling you exactly what's wrong - you're trying to refer to one field within the initializer of another. Put the declaration as normal:
Button[] myButtons;
and then in the constructor you can use:
myButtons = new[] { But_1, But_2, ... };
Related
I have seen it working with C# but not in Visual C++ 2015
System::Windows::Forms::Label^ mylabel= (gcnew System::Windows::Forms::Label());
mylabel->Name = L"pole";
mylabel->Text = "Hello";
this->Controls->Add(mylabel);
Note that mylabel is a temporary variable here.
Now the code work for C#
Control cc = this.Controls.Find("pole", true).First();
cc.text="New";
And I've tried this as there is no .First() or ->first(),
Control^ x = this->Controls->Find(L"pole", true);
and definitely an error shows
`cli::array<System::Windows::Forms::Control ^, 1> ^" cannot be used to initialize an entity of type "System::Windows::Forms::Control ^`"
How can I get that object as Control in runtime?
The Find method returns an array. In your C# example you call First() which returns the first item in the array (returning a reference to the Control). In the C++ example you do not call First() or do anything to retrieve a single item. That is why the error message indicates that you can't convert and array (note cli::array in error) to a Control reference.
I tried doing this in a class declaration.
public var Thing : Thing = Thing()
It says,
Variable used within its own initial value
If I remove the assignment then it gives.
Thing used within its own type
So no luck. Is it possible to use the same name for the property as the type? Its possible in C# :) At present I have lower cased the property name.
If you conform to the naming convention and declare variable names with a leading lowercase letter, it's possible.
public var thing : Thing = Thing()
If the following doesn't work:
public var thing: Thing = Thing()
There error is likely in the init method of Thing
Grails has a bug with regards to databinding in that it throws a cast exception when you're dealing with bad numerical input. JIRA: http://jira.grails.org/browse/GRAILS-6766
To fix this I've written the following code to manually handle the numerical input on the POGO class Foo located in src/groovy
void setPrice(String priceStr)
{
this.priceString = priceStr
// Remove $ and ,
priceStr = priceStr.trim().replaceAll(java.util.regex.Matcher.quoteReplacement('$'),'').replaceAll(',','')
if (!priceStr.isDouble()) {
errors.reject(
'trade.price.invalidformat',
[priceString] as Object[],
'Price:[{0}] is an invalid price.')
errors.rejectValue(
'price',
'trade.price.invalidformat')
} else {
this.price = priceStr.toDouble();
}
}
The following throws a null reference exception on the errors.reject() line.
foo.price = "asdf" // throws null reference on errors.reject()
foo.validate()
However, I can say:
foo.validate()
foo.price = "asdf" // no Null exception
foo.hasErrors() // false
foo.validate()
foo.hasErrors() // true
Where does errors come from when validate() is called?
Is there a way to add the errors property without calling validate() first?
I can't exactly tell you why, but you need to call getErrors() explicitly instead of accessing it as errors like a property. For some reason, Groovy isn't calling the method for it. So change the reject lines in setPrice() to
getErrors().reject(
'trade.price.invalidformat',
[priceString] as Object[],
'Price:[{0}] is an invalid price.')
getErrors().rejectValue(
'price',
'trade.price.invalidformat')
That is the easiest way to make sure the Errors object exists in your method. You can check out the code that adds the validation related methods to your domain class.
The AST transformation handling #Validateable augments the class with, among other things
a field named errors
public methods getErrors, setErrors, clearErrors and hasErrors
The getErrors method lazily sets the errors field if it hasn't yet been set. So it looks like what's happening is that accesses to errors within the same class are treated as field accesses rather than Java Bean property accesses, and bypassing the lazy initialization.
So the fix appears to be to use getErrors() instead of just errors.
The errors are add to your validateable classes (domain classes and classes that have the annotation #Validateable) dinamically.
Allowing the developer to set a String instead of a number doesn't seem a good way to go. Also, your validation will work only for that particular class.
I think that a better approach is to register a custom property editor for numbers. Here's a example with dates, that enable the transform of String (comming from the form) to Date with a format like dd/MM/yyyy. The idea is the same, as you will enforce that your number is parseable (eg. Integer.parseInt() will throw exception).
In your domain class, use the numeric type instead of String, so by code developers will not be allowed to store not number values.
I'm trying to see if there's a way to get a refference of an object which is outside the local (and global) scope, but who exists in memory.
Let's say in my program, i've instantiated an object whose reference is this:
{O:9*\PROGRAM=ZAVG_DELETE_THIS\CLASS=LCL_SMTH}
Far away after tons of calls, in a context where i wouldn't be able to access this object, could i do something like getting the reference of this object simply by knowing the above string?
I was looking into the cl_abap_*descr classes, but i haven't found a method that takes the 'program_name', 'class_name' and 'instance_number', to return the reference of an object.
I'm trying to do this for the purpose of debugging, not to build something that works.
[EDIT 1]:
I assumed that the o:9 string was required in order to get the reference of the object. As pointed out in the response of #mydoghasworms, this isn't the case. It seems that i only need the local name of the variable which holds the reference.
I hope I understand your question correctly, because I am not sure what you mean with "for the purpose of debugging", but here goes:
You can access the variables of another program that are loaded in the memory of the same session (I am pretty sure it does not need to be in the call stack) using:
ASSIGN ('(PROGRAM)VARIABLE') TO LV_LOCAL.
With reference variables, it becomes a bit more tricky, but here is an example that will help to demonstrate.
Here is our calling program that contains a reference variable LR_TEST which we want to access somewhere else. For the purpose of the demonstration, I make reference to a locally defined class (because that's what I gather from your question).
REPORT ZCALLER.
class lcl_test definition.
public section.
data: myval type i.
methods: my_meth exporting e_val type i.
endclass.
data: lr_test type ref to lcl_test.
CREATE OBJECT lr_test.
lr_test->MYVAL = 22.
perform call_me(zcallee).
class lcl_test implementation.
method my_meth.
* Export the attribute myval as param e_val.
e_val = myval.
endmethod.
endclass.
Here is the program in which we want to access a variable from the above program.
REPORT ZCALLEE.
form call_me.
field-symbols: <ref>.
data: ld_test type ref to object.
data: lv_val type i.
* Exhibit A: Gettinf a reference to a 'foreign' object instance
assign ('(ZCALLER)LR_TEST') to <ref>.
* <ref> now contains a reference to the class instance from the program
* ZCALLER (not very useful, except for passing around maybe)
* Exhibit B: Getting a public attribute from a 'foreign' class instance
assign ('(ZCALLER)LR_TEST->MYVAL') to <ref>.
* <ref> now contains the value of the attribute MYVAL
* Exhibit C: Getting a reference to an instance and calling a method
assign ('(ZCALLER)LR_TEST') to <ref>. "Again the class reference
if sy-subrc = 0. "Rule: Always check sy-subrc after assign before
"accessing a field symbol! (but you know that)
ld_test = <ref>. "Now we have a concrete handle
* Now we make a dynamic method call using our instance handle
CALL METHOD ld_test->('MY_METH')
IMPORTING
e_val = lv_val.
endif.
endform.
I was following a tutorial today that had me scratching my head for an hour. Consider:
public class MyClass {
public int getTotal() {
amount = 100;
return amount;
}
}
and an excerpt from a JSP:
<p>Total: ${objectOfTypeMyClass.total}</p> //object instantiated elsewhere
Nowhere in the code was an instance variable named "total" ever declared or used. The only reference to the word "total" in the whole project (other than in the JSP) was the method getTotal().
So after some desperate last-ditch experimentation, it appears that Expression Language evaluates ${someObject.var} as "call the getVar() method of the someObject object.
I worked with this long tutorial for over a week thinking that ${someObject.var} was saying "directly fetch the saved instance variable "var" from someObject.
Did I have it wrong the whole time and is my observation correct that in order to reference any instance variable using EL, you have to provide a corresponding getter method named getVarname() where "Varname" is the name of the instance variable?
Also, EL seems to be case-insensitive in this regard. In my example above, "total" in ${objectOfTypeMyClass.total} is all lowercase where the method getTotal() has a capital "T".
And while we're at it, why don't we need to instantiate the variable "total"? I guess EL isn't actually referencing an instance variable...just a getter method?
What gives?
Did I have it wrong the whole time and is my observation correct that in order to reference any instance variable using EL, you have to provide a corresponding getter method named getVarname() where "Varname" is the name of the instance variable?
That's correct. EL adheres the JavaBeans specification as described in the EL specification.
Also, EL seems to be case-insensitive in this regard. In my example above, "total" in ${objectOfTypeMyClass.total} is all lowercase where the method getTotal() has a capital "T".
No, it's certainly not case insensitive. It's specified behaviour. ${bean.Total} would not have worked.
And while we're at it, why don't we need to instantiate the variable "total"? I guess EL isn't actually referencing an instance variable...just a getter method?
It's because it's supposed to adhere the Javabean specification.
All with all, read the both specifications and everything will be clear :)
See also:
What are the advantages of Javabeans?
The . in objectOfTypeMyClass.total is the JSTL EL Dot Operator. It can do a few different things. Including:
map.key accessed a value from map stored under key. or
object.property accesses property from object using "JavaBeans" conventions.
This should work:
public class MyClass {
private int total = 100;
public int getTotal() {
return total;
}
...
}