So, I have a ListView that is x:Bind to a list and a DataTemplate.
The DataTemplate has an Elipse filled with an ImageBrush.
Everything works as it should but:
If an item in the list has a Null value for its string URL image property, the app crashes.
I have tried setting a TargetNullValue but my problem is that the X:DataType of the template is a class from an API, so I cant control it. I want to have an image as a default value in case the item has an image value of null.
In other words, if the item's image URL property is Null, I want XAML to load a predefined image from my Assets folder.
The problem is that because I have set my DataType as the class, anything I x:Bind to has to be within that class.
<Ellipse Width="40" Height="40">
<Ellipse.Fill>
<ImageBrush ImageSource="{x:Bind IconUrl, Mode=OneWay,TargetNullValue=/Assets/NoAvatarIcon.png}"/>
</Ellipse.Fill>
</Ellipse>
The above for example doesn't work for a Null string in ImageSource as the Path is set to the Class.
Right? Any workarounds?
The FallbackValue in Binding and x:Bind is different.
In Binding, FallbackValue is the value to use when the binding is unable to return a value.
A binding uses FallbackValue for cases where the Path doesn't evaluate on the data source at all, or if attempting to set it on the source with a two-way binding throws an exception that's caught by the data binding engine. FallbackValue is also used if the source value is the dependency property sentinel value DependencyProperty.UnsetValue.
But in x:Bind, FallbackValue specifies a value to display when the source or path cannot be resolved. It can't work with DependencyProperty.UnsetValue.
For your scenario, you can use Converter to operate DependencyProperty.UnsetValue just like following code.
public class ImageConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, string language)
{
object res;
res = (value == null ? false : true) ? string.IsNullOrEmpty(value.ToString()) ? null : new BitmapImage(new Uri(value.ToString())) : null;
return res;
}
public object ConvertBack(object value, Type targetType, object parameter, string language)
{
throw new NotImplementedException();
}
}
Usage in Xaml File
<Page.Resources>
<local:ImageConverter x:Key="cm" />
</Page.Resources>
<StackPanel Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<ListView x:Name="MyListView" ItemsSource="{x:Bind Items}">
<ListView.ItemTemplate>
<DataTemplate x:DataType="local:HeadPhoto">
<Ellipse Width="40" Height="40">
<Ellipse.Fill>
<ImageBrush ImageSource="{x:Bind PicUri,TargetNullValue=/Assets/pic.png,Converter={StaticResource cm }}" />
</Ellipse.Fill>
</Ellipse>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackPanel>
</Page>
Placeholder image effect.
Related
I am creating a web application, where you have to read a list of objects / entities from a DB and populate it in a JSF <h:selectOneMenu>. I am unable to code this. Can someone show me how to do it?
I know how to get a List<User> from the DB. What I need to know is, how to populate this list in a <h:selectOneMenu>.
<h:selectOneMenu value="#{bean.name}">
...?
</h:selectOneMenu>
Based on your question history, you're using JSF 2.x. So, here's a JSF 2.x targeted answer. In JSF 1.x you would be forced to wrap item values/labels in ugly SelectItem instances. This is fortunately not needed anymore in JSF 2.x.
Basic example
To answer your question directly, just use <f:selectItems> whose value points to a List<T> property which you preserve from the DB during bean's (post)construction. Here's a basic kickoff example assuming that T actually represents a String.
<h:selectOneMenu value="#{bean.name}">
<f:selectItems value="#{bean.names}" />
</h:selectOneMenu>
with
#ManagedBean
#RequestScoped
public class Bean {
private String name;
private List<String> names;
#EJB
private NameService nameService;
#PostConstruct
public void init() {
names = nameService.list();
}
// ... (getters, setters, etc)
}
Simple as that. Actually, the T's toString() will be used to represent both the dropdown item label and value. So, when you're instead of List<String> using a list of complex objects like List<SomeEntity> and you haven't overridden the class' toString() method, then you would see com.example.SomeEntity#hashcode as item values. See next section how to solve it properly.
Also note that the bean for <f:selectItems> value does not necessarily need to be the same bean as the bean for <h:selectOneMenu> value. This is useful whenever the values are actually applicationwide constants which you just have to load only once during application's startup. You could then just make it a property of an application scoped bean.
<h:selectOneMenu value="#{bean.name}">
<f:selectItems value="#{data.names}" />
</h:selectOneMenu>
Complex objects as available items
Whenever T concerns a complex object (a javabean), such as User which has a String property of name, then you could use the var attribute to get hold of the iteration variable which you in turn can use in itemValue and/or itemLabel attribtues (if you omit the itemLabel, then the label becomes the same as the value).
Example #1:
<h:selectOneMenu value="#{bean.userName}">
<f:selectItems value="#{bean.users}" var="user" itemValue="#{user.name}" />
</h:selectOneMenu>
with
private String userName;
private List<User> users;
#EJB
private UserService userService;
#PostConstruct
public void init() {
users = userService.list();
}
// ... (getters, setters, etc)
Or when it has a Long property id which you would rather like to set as item value:
Example #2:
<h:selectOneMenu value="#{bean.userId}">
<f:selectItems value="#{bean.users}" var="user" itemValue="#{user.id}" itemLabel="#{user.name}" />
</h:selectOneMenu>
with
private Long userId;
private List<User> users;
// ... (the same as in previous bean example)
Complex object as selected item
Whenever you would like to set it to a T property in the bean as well and T represents an User, then you would need to bake a custom Converter which converts between User and an unique string representation (which can be the id property). Do note that the itemValue must represent the complex object itself, exactly the type which needs to be set as selection component's value.
<h:selectOneMenu value="#{bean.user}" converter="#{userConverter}">
<f:selectItems value="#{bean.users}" var="user" itemValue="#{user}" itemLabel="#{user.name}" />
</h:selectOneMenu>
with
private User user;
private List<User> users;
// ... (the same as in previous bean example)
and
#ManagedBean
#RequestScoped
public class UserConverter implements Converter {
#EJB
private UserService userService;
#Override
public Object getAsObject(FacesContext context, UIComponent component, String submittedValue) {
if (submittedValue == null || submittedValue.isEmpty()) {
return null;
}
try {
return userService.find(Long.valueOf(submittedValue));
} catch (NumberFormatException e) {
throw new ConverterException(new FacesMessage(String.format("%s is not a valid User ID", submittedValue)), e);
}
}
#Override
public String getAsString(FacesContext context, UIComponent component, Object modelValue) {
if (modelValue == null) {
return "";
}
if (modelValue instanceof User) {
return String.valueOf(((User) modelValue).getId());
} else {
throw new ConverterException(new FacesMessage(String.format("%s is not a valid User", modelValue)), e);
}
}
}
(please note that the Converter is a bit hacky in order to be able to inject an #EJB in a JSF converter; normally one would have annotated it as #FacesConverter(forClass=User.class), but that unfortunately doesn't allow #EJB injections)
Don't forget to make sure that the complex object class has equals() and hashCode() properly implemented, otherwise JSF will during render fail to show preselected item(s), and you'll on submit face Validation Error: Value is not valid.
public class User {
private Long id;
#Override
public boolean equals(Object other) {
return (other != null && getClass() == other.getClass() && id != null)
? id.equals(((User) other).id)
: (other == this);
}
#Override
public int hashCode() {
return (id != null)
? (getClass().hashCode() + id.hashCode())
: super.hashCode();
}
}
Complex objects with a generic converter
Head to this answer: Implement converters for entities with Java Generics.
Complex objects without a custom converter
The JSF utility library OmniFaces offers a special converter out the box which allows you to use complex objects in <h:selectOneMenu> without the need to create a custom converter. The SelectItemsConverter will simply do the conversion based on readily available items in <f:selectItem(s)>.
<h:selectOneMenu value="#{bean.user}" converter="omnifaces.SelectItemsConverter">
<f:selectItems value="#{bean.users}" var="user" itemValue="#{user}" itemLabel="#{user.name}" />
</h:selectOneMenu>
See also:
Our <h:selectOneMenu> wiki page
View-Page
<h:selectOneMenu id="selectOneCB" value="#{page.selectedName}">
<f:selectItems value="#{page.names}"/>
</h:selectOneMenu>
Backing-Bean
List<SelectItem> names = new ArrayList<SelectItem>();
//-- Populate list from database
names.add(new SelectItem(valueObject,"label"));
//-- setter/getter accessor methods for list
To display particular selected record, it must be one of the values in the list.
Roll-your-own generic converter for complex objects as selected item
The Balusc gives a very useful overview answer on this subject. But there is one alternative he does not present: The Roll-your-own generic converter that handles complex objects as the selected item. This is very complex to do if you want to handle all cases, but pretty simple for simple cases.
The code below contains an example of such a converter. It works in the same spirit as the OmniFaces SelectItemsConverter as it looks through the children of a component for UISelectItem(s) containing objects. The difference is that it only handles bindings to either simple collections of entity objects, or to strings. It does not handle item groups, collections of SelectItems, arrays and probably a lot of other things.
The entities that the component binds to must implement the IdObject interface. (This could be solved in other way, such as using toString.)
Note that the entities must implement equals in such a way that two entities with the same ID compares equal.
The only thing that you need to do to use it is to specify it as converter on the select component, bind to an entity property and a list of possible entities:
<h:selectOneMenu value="#{bean.user}" converter="selectListConverter">
<f:selectItem itemValue="unselected" itemLabel="Select user..."/>
<f:selectItem itemValue="empty" itemLabel="No user"/>
<f:selectItems value="#{bean.users}" var="user" itemValue="#{user}" itemLabel="#{user.name}" />
</h:selectOneMenu>
Converter:
/**
* A converter for select components (those that have select items as children).
*
* It convertes the selected value string into one of its element entities, thus allowing
* binding to complex objects.
*
* It only handles simple uses of select components, in which the value is a simple list of
* entities. No ItemGroups, arrays or other kinds of values.
*
* Items it binds to can be strings or implementations of the {#link IdObject} interface.
*/
#FacesConverter("selectListConverter")
public class SelectListConverter implements Converter {
public static interface IdObject {
public String getDisplayId();
}
#Override
public Object getAsObject(FacesContext context, UIComponent component, String value) {
if (value == null || value.isEmpty()) {
return null;
}
return component.getChildren().stream()
.flatMap(child -> getEntriesOfItem(child))
.filter(o -> value.equals(o instanceof IdObject ? ((IdObject) o).getDisplayId() : o))
.findAny().orElse(null);
}
/**
* Gets the values stored in a {#link UISelectItem} or a {#link UISelectItems}.
* For other components returns an empty stream.
*/
private Stream<?> getEntriesOfItem(UIComponent child) {
if (child instanceof UISelectItem) {
UISelectItem item = (UISelectItem) child;
if (!item.isNoSelectionOption()) {
return Stream.of(item.getValue());
}
} else if (child instanceof UISelectItems) {
Object value = ((UISelectItems) child).getValue();
if (value instanceof Collection) {
return ((Collection<?>) value).stream();
} else {
throw new IllegalStateException("Unsupported value of UISelectItems: " + value);
}
}
return Stream.empty();
}
#Override
public String getAsString(FacesContext context, UIComponent component, Object value) {
if (value == null) return null;
if (value instanceof String) return (String) value;
if (value instanceof IdObject) return ((IdObject) value).getDisplayId();
throw new IllegalArgumentException("Unexpected value type");
}
}
I'm doing it like this:
Models are ViewScoped
converter:
#Named
#ViewScoped
public class ViewScopedFacesConverter implements Converter, Serializable
{
private static final long serialVersionUID = 1L;
private Map<String, Object> converterMap;
#PostConstruct
void postConstruct(){
converterMap = new HashMap<>();
}
#Override
public String getAsString(FacesContext context, UIComponent component, Object object) {
String selectItemValue = String.valueOf( object.hashCode() );
converterMap.put( selectItemValue, object );
return selectItemValue;
}
#Override
public Object getAsObject(FacesContext context, UIComponent component, String selectItemValue){
return converterMap.get(selectItemValue);
}
}
and bind to component with:
<f:converter binding="#{viewScopedFacesConverter}" />
If you will use entity id rather than hashCode you can hit a collision- if you have few lists on one page for different entities (classes) with the same id
Call me lazy but coding a Converter seems like a lot of unnecessary work. I'm using Primefaces and, not having used a plain vanilla JSF2 listbox or dropdown menu before, I just assumed (being lazy) that the widget could handle complex objects, i.e. pass the selected object as is to its corresponding getter/setter like so many other widgets do. I was disappointed to find (after hours of head scratching) that this capability does not exist for this widget type without a Converter. In fact if you supply a setter for the complex object rather than for a String, it fails silently (simply doesn't call the setter, no Exception, no JS error), and I spent a ton of time going through BalusC's excellent troubleshooting tool to find the cause, to no avail since none of those suggestions applied. My conclusion: listbox/menu widget needs adapting that other JSF2 widgets do not. This seems misleading and prone to leading the uninformed developer like myself down a rabbit hole.
In the end I resisted coding a Converter and found through trial and error that if you set the widget value to a complex object, e.g.:
<p:selectOneListbox id="adminEvents" value="#{testBean.selectedEvent}">
... when the user selects an item, the widget can call a String setter for that object, e.g. setSelectedThing(String thingString) {...}, and the String passed is a JSON String representing the Thing object. I can parse it to determine which object was selected. This feels a little like a hack, but less of a hack than a Converter.
This is my first question here!
I am trying to pass a Map as parameter from a struts action to a report. I have inserted the map in the reportParameters map that are being passed to the jrxml file.
My question is whether this Map can be retrieved inside the jrxml file.
To be More precise, I declare it like this:
<parameter name="reportParams.testMap" class="java.util.Map"/>
and I want to use it like this:
<textField>
<reportElement style="StyleData" x="240" y="0" width="100" height="23"/>
<textElement textAlignment="Left" verticalAlignment="Top"/>
<textFieldExpression><![CDATA[testMap.get("AR")]]></textFieldExpression>
</textField>
Is it possible? Because I keep getting this error in my application server logs:
No such property: testMap for class: Blank32A4_1336385977531_38171
Error evaluating expression : Source text : testMap.get("AR")
Error evaluating expression : Source text : testMap.get("AR")
My action class looks like this:
#Injectable
#Results({
#Result(name = "success", type = "jasper", params={"location",
"report.jasper",
"connection", "statsConnection",
"dataSource", "translations",
"reportParameters","reportParams",
"format","PDF"})
})
public class LocalMapStatisticNewAction extends ActionSupport{
...
public String execute() {
reportParams = new Hashtable<String, Object>();
testMap = new Hashtable<String, String>();
testMap.put("AR", "Argentina");
testMap.put("ES", "Spain");
reportParams.put("testMap", testMap);
//Jasper code here
}
...
public Map<String, Object> getReportParams() {
return reportParams;
}
}
Any hint would be helpful!
It looks like it could be as simple as you referencing a parameter by the wrong name.
testMap.get("AR")
You don't have a parameter called testMap. You have a parameter called reportParams.testMap. Also, you need to refer to parameters like this:
$P{testMap}.get("AR")
Rename the parameter or rename the reference to the parameter, and you should be OK.
I have a f:convertDateTime with a pattern of mm/dd/yyyy. However, people are able to enter 2/19/78 and it would be 0078 rather then 1978 or 2078. I want to force people to enter in all 4 digits.
I tried using a regexPattern validator, but that is complaining because it wants a string and not a Date object. Seems that the converters fire first and validators validate the converted value?
I guess I could write a custom converter or validator, but this seems like such a simple thing I figure I'm doing something wrong.
The javadocs for the convertor say it is strict in matching the pattern, but I'm not seeing that?
Any ideas or suggestions?
thanks!
It's only strict for days/months, not for years. Here's an extract of relevance from SimpleDateFormat javadoc which <f:convertDateTime> is using under the covers:
For parsing, if the number of pattern letters is more than 2, the year is interpreted literally, regardless of the number of digits. So using the pattern "MM/dd/yyyy", "01/11/12" parses to Jan 11, 12 A.D.
It's by design indeed not possible to fire validators before converters. Essentially, this one should have thrown a ConverterException because the input is not in the proper format. I'd create a custom converter which validates the pattern beforehand. Something like this:
#FacesConverter("validatingPatternDateTimeConverter")
public class ValidatingPatternDateTimeConverter extends DateTimeConverter {
#Override
public Object getAsObject(FacesContext context, UIComponent component, String value) {
String regex = getMandatoryAttribute(component, "validateRegex");
String pattern = getMandatoryAttribute(component, "convertPattern");
if (value != null && !value.matches(regex)) {
throw new ConverterException(new FacesMessage(String.format("Invalid date, must be in pattern %s", pattern)));
}
setPattern(pattern);
return super.getAsObject(context, component, value);
}
#Override
public String getAsString(FacesContext context, UIComponent component, Object value) {
setPattern(getMandatoryAttribute(component, "convertPattern"));
return super.getAsString(context, component, value);
}
private String getMandatoryAttribute(UIComponent component, String name) {
String value = (String) component.getAttributes().get(name);
if (value == null || value.isEmpty()) {
throw new IllegalArgumentException(String.format("<f:attribute name=\"%s\"> is missing.", name));
}
return value;
}
}
which is to be used as follows:
<h:inputText value="#{bean.date}">
<f:converter converterId="validatingPatternDateTimeConverter" />
<f:attribute name="validateRegex" value="\d{1,2}/\d{1,2}/\d{4}" />
<f:attribute name="convertPattern" value="MM/dd/yyyy" />
</h:inputText>
I have a text box whose Text property has a TwoWay MultiBinding with UpdateSourceTrigger set to PropertyChanged. The first Binding is to a dependency property (Value) which has a PropertyChangedCallBack function that rounds the value to one decimal place.
The purpose of the text box is to perform the rounding as the user types rather than when the text box loses focus, hence why UpdateSourceTrigger is set to PropertyChanged.
The problem I am having is that if text is entered that does NOT result in Value changing, the Text property and Value become out of sync. Only if the rounding operation causes Value to change does Text get updated on the fly. E.g., if Text and Value are both 123.4 and the user types 1 after this, Value is rounded to the same value (123.4), but Text shows 123.41. However, if 9 is then typed after the 4, Value is rounded up to 123.5. And because of this actual change, Text is then updated to the same (123.5).
Is there any way of forcing a text box to update from its source even when the source hasn't changed since the last trigger? I have tried using BindingExpressionBase.UpdateTarget() but this only works when UpdateSourceTrigger is set to Explicit, which can't be used as Value no longer gets updated prior to a suitable time where UpdateTarget could be called (such as a TextInput handler). I have tried other methods such as explicitly updating the Text value from the bound Value, forcing an actual change to Value temporarily to invoke an update, but these "hacks" either don't work or cause other problems.
Any help would be greatly appreciated.
The code is below.
XAML snippet
<TextBox>
<TextBox.Text>
<MultiBinding Converter="{local:NumberFormatConverter}"
UpdateSourceTrigger="Explicit"
Mode="TwoWay">
<Binding Path="Value"
RelativeSource="{RelativeSource AncestorType={x:Type Window}}"
Mode="TwoWay" />
</MultiBinding>
</TextBox.Text>
</TextBox>
C# snippet
public static readonly DependencyProperty ValueProperty =
DependencyProperty.Register(
"Value", typeof(decimal), typeof(MainWindow),
new FrameworkPropertyMetadata(0m,
new PropertyChangedCallback(OnValueChanged)));
private static void OnValueChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
{
obj.SetValue(ValueProperty, Math.Round((decimal)args.NewValue, 1));
}
Converter class required
public class NumberFormatConverter : MarkupExtension, IMultiValueConverter
{
public static NumberFormatConverter Instance { private set; get; }
static NumberFormatConverter()
{
Instance = new NumberFormatConverter();
}
public override object ProvideValue(IServiceProvider serviceProvider_)
{
return Instance;
}
#region Implementation of IMultiValueConverter
public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
{
return values[0].ToString();
}
public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
{
var result = 0m;
if (value != null)
{
decimal.TryParse(value.ToString(), out result);
}
return new object[] { result };
}
#endregion
}
I did a little digging on the Internet, and it turns out this was broken in WPF 4. Someone with an almost-identical problem to me posted here:
http://www.go4answers.com/Example/textbox-shows-old-value-being-coerced-137799.aspx
'Answer 8' states this was broken in WPF 4 and suggests a solution, which is to actually use UpdateSourceTrigger="Explicit" but to handle the TextChanged event and call BindingExpression.UpdateSource() to force changes in the text box to be reflected in the underlying value as if UpdateSourceTrigger="PropertyChanged", as per this post:
Coerce a WPF TextBox not working anymore in .NET 4.0
I implemented this, but lo and behold there were further side effects, in particular that every keystroke caused the caret to jump to the start of the text box due to updating the source and raising a PropertyChanged event. And also, any leading or trailing zeros or decimal places entered with the intention of entering further digits would get wiped out immediately. So, a simple condition to check the parsed decimal value of the text box versus the underlying value resolved this.
The following event handler is all that was needed:
private void TextBox_TextChanged(object sender, TextChangedEventArgs e)
{
var tb = (TextBox)e.Source;
MultiBindingExpression binding = BindingOperations.GetMultiBindingExpression(tb, TextBox.TextProperty);
decimal result = 0m;
decimal.TryParse(tb.Text, out result);
if ((decimal)GetValue(ValueProperty) != result && binding != null)
{
int caretIndex = tb.CaretIndex;
binding.UpdateSource();
tb.CaretIndex = caretIndex;
}
}
In spark when sending a view model to the view when a collection is empty is causing me some headaches like so:
<input value="model.addresses[0].street" />
Where "model.addresses" may be empty and thus gives an NRE.
Is there anyway to handle this other than populating the collections prior to rendering. This is a bit of a pain as it reqiures some custom processing to make sure they are populated. I was thinking the spark conditional attribute would work:
<input value="model.addresses[0] != null?model.addresses.street" />
But I feel like there may be a better way to handle these situations.
I see couple of other options:
Use partial view for list items and check for NULLs once in there.
Add extension method to simplify the NULL checks.
These are one of the most used extension methods I have written for myself:
public static TResult PropGet<TObject, TResult>(this TObject obj, Func<TObject, TResult> getter, TResult defaultValue) {
if (ReferenceEquals(obj, null))
return defaultValue;
var res = getter.Invoke(obj);
return ReferenceEquals(res, null) ? defaultValue : res;
}
public static TResult PropGet<TObject, TResult>(this TObject obj, Func<TObject, TResult> getter) {
return PropGet(obj, getter, default(TResult));
}
So on your view you could write this:
<input value="model.addresses[0].PropGet(a => a.street)" />
From spark documentation:
The syntax $!{expression} can also be used if you want to ensure any null values and NullReferenceException that result from the expression will produce no output at all.
http://sparkviewengine.com/documentation/expressions#Nullsinexpressions