i have a little question for Java-Fx and Observable-lists. I want to build a Timetable for a couple of persons. There for i have a Person-Class, in which i want to give every Person its own Observable-list in the Constructor. Someone got a notation for this case? i have already tried so stuff but nothing seems to work. On one hand i need an Attribute for the List to build a getter-Method for it and i want to give each Person its own List.
this is my Attribut:
ObservableList personTableList = FXCollections.observableArrayList();
now i need the notation for the Constructor!
thanks, Manuel
I don't know if I understand you exactly what you want to gain.
E.g.:
public class Person {
private ObservableList personTableList;
public Person() {
this(null);
}
public Person(ObservableList list) {
if (list == null) {
this.personTableList = FXCollections.observableArrayList();
} else {
this.personTableList = list;
}
}
public ObservableList getPersonTableList() {
return this.personTableList;
}
public void setPersonTableList(ObservableList list) {
this.personTableList = list;
}
}
Using e.g.:
new Person();
Related
I have some code that generates answers based on the user input. But in somecases i need to update the values later by calling SetAnswers But when i compile my code i get the following error:
NullReferenceException: Object reference not set to an instance of an object
I get this error on the line marked by the arrow.
See below for my code:
public class Generate_Questions : MonoBehaviour{
public Question q5, q4;
void Start(){
q4 = create_question("Select object to edit", EXTERNAL);
Visual_Question vq1 = new Visual_Question(1, q4, new vector(1,1,1), Ui, Canvas);
vq1.draw_question();
}
void Update(){
}
public class Visual_Question : Generate_Questions{
public Visual_Question(int order_id, Question q, Vector2 loc, Dictionary<string, RectTransform> ui, RectTransform canvas){
}
public void draw_question(){
q4.SetAnswers(new Answer[]{ <--------- this generates the error.
new Answer(null, "Select an option")
});
}
}
public class Question{
public string text;
public int answers_loc;
public List<Answer> answers;
public Question(string q_text, int answers_loc){
answers = new List<Answer>();
this.text = q_text;
this.answers_loc = answers_loc;
}
public void SetAnswers(Answer[] c_answers){
foreach(Answer answer in c_answers){
this.answers.Add(answer);
}
}
public bool CheckIfAnswersAvailable(){
if(answers.Count > 0){
return true;
}else{
return false;
}
}
public int QuestionLocation(){
return answers_loc;
}
}
public Question create_question(string text, int a_type){
Question Q = new Question(text, a_type);
return Q;
}
public interface IAnswer{
string GetText();
string GetDataType();
object GetValue();
Question GetNextQuestion();
}
public class Answer : IAnswer{
public string text;
public Question next = null;
public int? action = null;
public Element obj = null;
public string property = null;
public float? value = null;
public Answer(Question next, string text){
this.text = text;
this.next = next;
}
public Answer(Question next, string text, Element obj, int? action){
this.action = action;
this.text = text;
this.next = next;
this.obj = obj;
}
public Answer(Question next, string text, Element obj, int? action, string property, float? value){
this.action = action;
this.next = next;
this.text = text;
this.obj = obj;
this.property = property;
this.value = value;
}
public string GetText(){
return text;
}
public string GetDataType(){
throw new System.NotImplementedException();
}
public object GetValue(){
return value;
}
public Question GetNextQuestion(){
return next;
}
}
}
how would i go about fixing this problem? I am a complete newbie to c#. So my question may be already answered but i just dont know what i am looking for.
I assume that IAnswer[] is an interface and since you are trying to initialize an abstract object you get that runtime exception
NullReferenceException: Object reference not set to an instance of an object
if you want to create instance of IAnswer object you have to restructure it like class or structure.
Your class Visual_Question derives from Generate_Questions, so the member q4 that you use en draw_question is not initialized. This is not the member of Generated_Questions but a member of Visual_Question that is not initialized.
In Generate_Questions you are creating a new instance of Visual_Question and then immediately calling draw_question on that new instance. You now have 2 instances of a question (both derive from Generate_Questions), but only one of them has had the Start method, which initializes q4 called. If, however, you attempt to call Start from your second instance, you're going to find yourself in an infinite series of recursive calls and quickly crash with a different error (a stack overflow in this case).
One issue with the current code is that Generate_Questions sounds more like an action than a class. I'd suggest removing the inheritance from Visual_Question and make that an interface that you would implement on Question. Question should probably have the create_question method removed. That probably belongs in a MonoBehavior script (technically it's a factory method -- look up the factory pattern -- I'm not going to go into it here since this is a beginner topic).
Something like (obviously not complete):
public class Generate_Questions : MonoBehaviour
{
private IVisualQuestion q4;
void Start()
{
q4 = new Question("Select object to edit", EXTERNAL);
q4.DrawQuestion(new vector(1,1,1), Ui, Canvas)
}
void Update() {}
}
public interface IVisualQuestion
{
void DrawQuestion(Vector2 loc, Dictionary<string, RectTransform> ui, RectTransform canvas);
}
public class Question : IVisualQuestion
{
// ... insert the Question constructor and code here ...
// Implement VisualQuestion interface
public void DrawQuestion(Vector2 loc, Dictionary<string, RectTransform> ui, RectTransform canvas)
{
this.SetAnswers(new Answer[]{new Answer(null, "Select an option")});
}
}
In general, you probably don't need inheritance. As you learn more C#, you'll discover that when inheritance is going to help it will be clear. More often than not, using an interface is a far better and flexible approach. As a commenter noted, you probably don't want to inherit from MonoBehavior. You really only need that for classes that the Unity Engine is going to directly handle.
Another note: the convention in C# is to name methods, variables, etc. in PascalCase, not using underscores to separate words.
I cannot seem to access an array of custom objects (that is a column in a Parse table) after querying for it and receiving the results.
I have a simple custom class call "TextEntry" that contains 2 strings.
public class TextEntry
{
public string key;
public string text;
public TextEntry() { }
}
I have a ParseObject subclass called "LocalePO", which has an IList member in addition to other native types.
[ParseClassName("LocalePO")]
public class LocalePO : ParseObject
{
[ParseFieldName("version")]
public int version
{
get { return GetProperty<int>("version"); }
set { SetProperty<int>(value, "version"); }
}
[ParseFieldName("code")]
public string code
{
get { return GetProperty<string>("code"); }
set { SetProperty<string>(value, "code"); }
}
[ParseFieldName("name")]
public string name
{
get { return GetProperty<string>("name"); }
set { SetProperty<string>(value, "name"); }
}
[ParseFieldName("keypair")]
public IList<object> keypair
{
get { return GetProperty<IList<object>>("keypair"); }
set { SetProperty<IList<object>>(value, "keypair"); }
}
public LocalePO() { }
}
I can query to Parse and successfully return a LocalePO object, but I cannot access the specific "TextEntry" members of the "keypair" List afterwards.
var cloudQuery = new ParseQuery<LocalePO>();
var queryTask = cloudQuery.FirstAsync();
// wait for query to return
while (!queryTask.IsCompleted) yield return null;
LocalePO locale = queryTask.Result;
int CloudVersion = locale.version; // this works
List<TextEntry> list = new List<TextEntry>();
list = locale.keypair.Cast<TextEntry>.ToList(); // this doesn't work
foreach (var item in locale.keypair)
{
var entry = item as TextEntry; // this does not work
TextEntry entry = (TextEntry)item; // this doesn't work either
// this is my current solution which works but seems terrible
string json = JsonConvert.SerializeObject(item);
TextEntry entry = JsonConvert.DeserializeObject<TextEntry>(json);
list.Add(entry);
}
I feel like I am overlooking something very simple here, but I just want to convert the data I pull from Parse to local objects so I can use the data throughout the app logic.
It seems to me that Parse prefers the IList of type "object"vs an IList of type "TextEntry" type for the ParseFieldName. For example, Parse always returns null for the field if I have the following:
[ParseFieldName("keypair")]
public IList<TextEntry> keypair
{
get { return GetProperty<IList<TextEntry>>("keypair"); }
set { SetProperty<IList<TextEntry>>(value, "keypair"); }
}
Perhaps I should derive TextEntry from ParseObject too? I'm so confused.
Any help would be appreciated.
Thanks!
Try this:
var cloudQuery = new ParseQuery<LocalePO>();
cloudQuery .Include("keypair");
var queryTask = cloudQuery.FirstAsync();
TextEntry will need to derive from parseObject and you will need to register it as a subclass.
Here is an example of a query I am using which has 2 levels of nested iList's of parseObject subclasses
ParseObject.RegisterSubclass<ProgramDataParse>();
ParseObject.RegisterSubclass<WorkoutDataParse>();
ParseObject.RegisterSubclass<ExerciseDataParse>();
var programQuery = new ParseQuery<ProgramDataParse>()
.OrderByDescending("createdAt").Limit(2)
.Include("workouts")
.Include("workouts.exercises");
I think I'm missing something fundamental when implementing a LinqToHql generator class.
I've successfully registered the SQL Server 2008 contains query using a custom dialect with this registration:
RegisterFunction("contains", new StandardSQLFunction("contains", null));
I have only one class with a full text index to be queried:
public class SearchName
{
public virtual Guid Id {get; set;}
public virtual string Name {get; set;} // this is the search field
}
The contains function works properly in HQL:
var names = Session.CreateQuery("from SearchName where contains(Name,:keywords)")
.SetString("keywords", "john")
.List();
and the generated SQL is perfect:
select searchname0_.Id as Id4_,
searchname0_.Name as Name4_
from Search_Name searchname0_
where contains(searchname0_.Name, 'john' /* #p0 */)
The next challenge was to implement the Linq to HQL generator:
public class MyLinqtoHqlGeneratorsRegistry :
DefaultLinqToHqlGeneratorsRegistry
{
public MyLinqtoHqlGeneratorsRegistry()
{
this.Merge(new ContainsGenerator());
}
}
public class ContainsGenerator : BaseHqlGeneratorForMethod
{
public ContainsGenerator()
{
SupportedMethods = new[] {
ReflectionHelper.GetMethodDefinition<SearchName>(d => d.Name.Contains(String.Empty))
};
}
public override HqlTreeNode BuildHql(MethodInfo method,
System.Linq.Expressions.Expression targetObject,
ReadOnlyCollection<System.Linq.Expressions.Expression> arguments,
HqlTreeBuilder treeBuilder, IHqlExpressionVisitor visitor)
{
return treeBuilder.MethodCall("contains",
visitor.Visit(targetObject).AsExpression(),
visitor.Visit(arguments[0]).AsExpression()
);
}
}
}
Calling the method like this:
var namesLinq = Session.Query<SearchName>().Where(x=> x.Name.Contains("john")).ToList();
Unfortunately, this doesn't seem to override the built-in Contains method, and the generated SQL is wrong:
select searchname0_.Id as Id4_,
searchname0_.Name as Name4_
from Search_Name searchname0_
where searchname0_.Name like ('%' + 'john' /* #p0 */ + '%')
Is it not possible to override the default Contains method, or have I just made a silly mistake?
PS - I'm using NHibernate 3.3.1.4000
OK, I've finally figured it out!
First, I managed to delete the registration code from my configuration:
...
.ExposeConfiguration(cfg =>
{
cfg.LinqToHqlGeneratorsRegistry<MyLinqtoHqlGeneratorsRegistry>();
...
}
Second, don't try to override the existing Linq behaviors. I moved my Contains extension method to the full-text class.
Third, build the Hql tree correctly.
For others trying to implement a SQL 2008 Free-text contains search, here's the complete implementation:
public static class DialectExtensions
{
public static bool Contains(this SearchName sn, string searchString)
{
// this is just a placeholder for the method info.
// It does not otherwise matter.
return false;
}
}
public class MyLinqtoHqlGeneratorsRegistry : DefaultLinqToHqlGeneratorsRegistry
{
public MyLinqtoHqlGeneratorsRegistry()
: base()
{
RegisterGenerator(ReflectionHelper.GetMethod(() =>
DialectExtensions.Contains(null, null)),
new ContainsGenerator());
}
}
public class ContainsGenerator : BaseHqlGeneratorForMethod
{
string fullTextFieldName = "Name";
public ContainsGenerator()
: base()
{
SupportedMethods = new[] {
ReflectionHelper.GetMethodDefinition(() =>
DialectExtensions.Contains(null, null))
};
}
public override HqlTreeNode BuildHql(MethodInfo method,
System.Linq.Expressions.Expression targetObject,
ReadOnlyCollection<System.Linq.Expressions.Expression> arguments,
HqlTreeBuilder treeBuilder, IHqlExpressionVisitor visitor)
{
// cannot figure out how to interrogate the model class to get an
// arbitrary field name...
// perhaps the RegisterGenerator() call above could be used to pass a
// property name to the ContainsGenerator constructor?
// in our case, we only have one full text searchable class, and its
// full-text searchable field is "Name"
HqlExpression[] args = new HqlExpression[2] {
treeBuilder.Ident(fullTextFieldName).AsExpression(),
visitor.Visit(arguments[1]).AsExpression()
};
return treeBuilder.BooleanMethodCall("contains", args);
}
}
For the above to work, you must have declared and used your custom dialect:
public class CustomMsSql2008Dialect : NHibernate.Dialect.MsSql2008Dialect
{
public CustomMsSql2008Dialect()
{
RegisterFunction(
"contains",
new StandardSQLFunction("contains", null)
);
}
}
Then you can use your new contains search this way:
var namesLinq = Session.Query<SearchName>().Where(x => x.Contains("john")).ToList();
... and the resulting SQL is perfect! (at least if you only have one table you're performing full-text searches on)
EDIT: UPDATED IMPLEMENTATION TO SUPPORT MORE THAN ONE FULLTEXT 'Contains' SEARCH PER QUERY.
Here's the revised version:
public static class DialectExtensions
{
public static bool FullTextContains(this string source, string pattern)
{
return false;
}
}
public class MyLinqtoHqlGeneratorsRegistry : DefaultLinqToHqlGeneratorsRegistry
{
public MyLinqtoHqlGeneratorsRegistry()
: base()
{
RegisterGenerator(ReflectionHelper.GetMethod(() => DialectExtensions.FullTextContains(null, null)),
new FullTextContainsGenerator());
}
}
public class FullTextContainsGenerator : BaseHqlGeneratorForMethod
{
public FullTextContainsGenerator()
{
SupportedMethods = new[] { ReflectionHelper.GetMethod(() => DialectExtensions.FullTextContains(null, null)) };
}
public override HqlTreeNode BuildHql(MethodInfo method,
System.Linq.Expressions.Expression targetObject,
ReadOnlyCollection<System.Linq.Expressions.Expression> arguments,
HqlTreeBuilder treeBuilder, IHqlExpressionVisitor visitor)
{
HqlExpression[] args = new HqlExpression[2] {
visitor.Visit(arguments[0]).AsExpression(),
visitor.Visit(arguments[1]).AsExpression()
};
return treeBuilder.BooleanMethodCall("contains", args);
}
}
To use the revised version, the syntax is slightly different:
var namesLinq = Session.Query<SearchName>().Where(x => x.Name.FullTextContains("john")).ToList();
In order to find walk-around for absence RelativeSource in MvvmCross, I used Stuart's suggestion and implemented WrappingList
MVVMCross changing ViewModel within a MvxBindableListView
However, I see this trace every bind it happens and I wonder, how worse it is:
Binding to IEnumerable rather than IList - this can be inefficient,
especially for large lists
Maybe there are any other suggestions?
public class WrappingCommandsList<T> : IList<WrappingCommandsList<T>.Wrapped>
{
private readonly List<T> _realList;
private readonly Action<T> _realActionOnClick;
public class Wrapped
{
public IMvxCommand ClickCommand { get; set; }
public T TheItem { get; set; }
}
public WrappingCommandsList(List<T> realList, Action<T> realActionOnClick)
{
_realList = realList;
_realActionOnClick = realActionOnClick;
}
private Wrapped Wrap(T item)
{
return new Wrapped()
{
ClickCommand = new MvxCommand(() => _realActionOnClick(item)),
TheItem = item
};
}
public WrappingCommandsList<T>.Wrapped this[int index]
{
get
{
return Wrap(_realList[index]);
}
set
{
throw new NotImplementedException();
}
}
public int Count
{
get { return _realList.Count; }
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
public IEnumerator<WrappingCommandsList<T>.Wrapped> GetEnumerator()
{
foreach (var item in _realList)
{
yield return Wrap(item);
}
}
How inefficient depends on the length of your list and how far down it the used has scrolled.
eg if the user is showing item 93,256 on the screen then the only way for the list adapter to find item 93,256 is to get the enumerator and to call MoveNext 93,256 times.
Whereas if your list only has 5 items the problem is bounded by 5.
For your particular WrappingCommandsList try implementing IList as well as IList<T> - the mvx code can't generate the IList<T> accessors at runtime because of xamarin.ios AoT compilation restrictions.
Is it possible to extend LINQ-to-SQL entity-classes with constructor-methods and in the same go; make that entity-class inherit from it's data-context class?--In essence converting the entity-class into a business object.
This is the pattern I am currently using:
namespace Xxx
{
public class User : Xxx.DataContext
{
public enum SiteAccessRights
{
NotRegistered = 0,
Registered = 1,
Administrator = 3
}
private Xxx.Entities.User _user;
public Int32 ID
{
get
{
return this._user.UsersID;
}
}
public Xxx.User.SiteAccessRights AccessRights
{
get
{
return (Xxx.User.SiteAccessRights)this._user.UsersAccessRights;
}
set
{
this._user.UsersAccessRights = (Int32)value;
}
}
public String Alias
{
get
{
return this._user.UsersAlias;
}
set
{
this._user.UsersAlias = value;
}
}
public User(Int32 userID)
{
var user = (from u in base.Users
where u.UsersID == userID
select u).FirstOrDefault();
if (user != null)
{
this._user = user;
}
else
{
this._user = new Xxx.Entities.User();
base.Users.InsertOnSubmit(this._user);
}
}
public User(Xxx.User.SiteAccessRights accessRights, String alias)
{
var user = (from u in base.Users
where u.UsersAccessRights == (Int32)accessRights && u.UsersAlias == alias
select u).FirstOrDefault();
if (user != null)
{
this._user = user;
}
else
{
this._user = new Xxx.Entities.User
{
UsersAccessRights = (Int32)accessRights,
UsersAlias = alias
};
base.Users.InsertOnSubmit(this._user);
}
}
public void DeleteOnSubmit()
{
base.Users.DeleteOnSubmit(this._user);
}
}
}
Update:
Notice that I have two constructor-methods in my User class. I'd like to transfer those to the User entity-class and extend the User entity-class on it's data-context class, so that the data-context is available to the entity-class on "new-up".
Hope this makes sense.
Rick Strahl has a number of really good articles that address what I think you are looking for. Check out his list of Linq Articles Here
Inheriting an entity from a data context is a bad idea. They are two discrete objects and are designed to operate that way. Doing this will cause all sorts of issues least of all problems with trying to submit a bunch of related changes together at the same time - going through multiple data contexts will cause this to fail as each tries to work independently.
It doesn't seem to make sense to make an entity a type of DataContext. It doesn't need to be a DataContext in order to be considered a business object, nor do you necessarily need to create a type that contains the original entity. It might be better to just extend the entity class and contain a reference to a DataContext using composition:
namespace Xxx.Entities
{
public partial class User : IDisposable
{ DataContext ctx;
public static GetUserByID(int userID)
{ var ctx = new DataContext();
var user = ctx.Users.FirstOrDefault(u=>u.UsersID == userID);
if (user == null)
{
user = new User();
ctx.Users.InsertOnSubmit(user);
}
user.ctx = ctx;
return user;
}
public void Dispose() { if (ctx != null) ctx.Dispose(); }
}
}
If you just want the property names to be different than the database column names, do that in the mapping file.