java.beans
Interface PropertyEditor
- PropertyEditorSupport
PropertyEditors are custom GUI editors for specific types of values.
A PropertyEditor can be used, for example, if you are editing a type of value
that can be more easily represented graphically, such as a Point, or one that
can be more easily represented by a list, such as a boolean (true/false).
A PropertyEditor must be able to display its contents when asked to and
be able to allow the user to change its underlying field value. However, it
is not the PropertyEditor's responsibility to make the change to the
underlying Object; in fact, the PropertyEditor does not even know about the
Object it is actually editing--only about the property it is currently
editing. When a change is made to the property, the PropertyEditor must
simply fire a PropertyChangeEvent and allow the RAD tool to actually set
the property in the underlying Bean.
PropertyEditors should not change the Objects they are given by setValue().
These Objects may or may not be the actual Objects which are properties of
the Bean being edited. Instead, PropertyEditors should create a new Object
and fire a PropertyChangeEvent with the old and new values.
PropertyEditors also must support the ability to return a Java
initialization string. See the getJavaInitializationString() method for
details.
There are several different ways a PropertyEditor may display and control
editing of its value. When multiple types of input and display are
given by a single PropertyEditor, the RAD tool may decide which of the call
to support. Some RAD tools may even be text-only, so even if you support
a graphical set and get, it may choose the text set and get whenever it can.
- Every PropertyEditor must support getValue() and setValue(). For
setValue(), the component must only support it when the argument is
the same type that the PropertyEditor supports.
- Every PropertyEditor must support getJavaInitializationString().
- You may support painting the value yourself if you wish. To do this,
have isPaintable() return true and implement the paintValue() method.
This method does not determine in any way how the value is edited;
merely how it is displayed.
- Let the caller of the PropertyEditor give the user a text input. Do
this by returning a non-null String from getAsText(). If you support
text input, you *must* support setAsText().
- Give the caller a set of possible values, such as "true"/"false", that
the user must select from. To do this, return the list of Strings
from the getTags() method. The RAD tool may choose to implement the
user input any way it wishes, and only guarantees that setAsText() will
only be called with one of the Strings returned from getTags().
- You may support a whole custom editing control by supporting
getCustomEditor(). To do this, return true from supportsCustomEditor()
and return a Component that does the job. It is the component's job,
or the PropertyEditor's job, to make sure that when the editor changes
its value, the PropertyChangeEvent is thrown.
The PropertyEditor for a particular Bean can be found using the
PropertyEditorManager class, which goes through a series of different
checks to find the appropriate class.
A PropertyChangeEvent should be thrown from the PropertyEditor whenever a
bound property (a property PropertyDescriptor.isBound() set to true)
changes. When this happens, the editor itself should *not* change the value
itself, but rather allow the RAD tool to call setValue() or setAsText().
getAsText
public String getAsText()
Get the value of this property in String format.
Many times this can simply use Object.toString().
Return null if you do not support getAsText()/setAsText().
setAsText(getAsText()) should be valid; i.e. the stuff you spit out in
getAsText() should be able to go into setAsText().
- the value of this property in String format.
getCustomEditor
public Component getCustomEditor()
The RAD tool calls this to grab the component that can edit this type.
The component may be painted anywhere the RAD tool wants to paint it--
even in its own window.
The component must hook up with the PropertyEditor and, whenever a
change to the value is made, fire a PropertyChangeEvent to the source.
- the custom editor for this property type.
getJavaInitializationString
public String getJavaInitializationString()
Get a Java language-specific String which could be used to create an Object
of the specified type. Every PropertyEditor must support this.
The reason for this is that while most RAD tools will serialize the Beans
and deserialize them at runtime, some RAD tools will generate code that
creates the Beans. Examples of Java initialization strings would be:
2"I am a String"new MyObject(2, "String", new StringBuffer())
- the initialization string for this object in Java.
getTags
public String[] getTags()
Get a list of possible Strings which this property type can have.
The value of these will be used by the RAD tool to construct some sort
of list box or to check text box input, and the resulting String passed
to setAsText() should be one of these. Note, however, that like most things
with this mammoth, unwieldy interface, this is not guaranteed. Thus, you
must check the value in setAsText() anyway.
- the list of possible String values for this property type.
getValue
public Object getValue()
Accessor method to get the current value the PropertyEditor is working with.
If the property type is native, it will be wrapped in the appropriate
wrapper type.
- the current value of the PropertyEditor.
isPaintable
public boolean isPaintable()
The RAD tool calls this to find out whether the PropertyEditor can paint itself.
- true if it can paint itself graphically, false if it cannot.
paintValue
public void paintValue(Graphics g,
Rectangle bounds)The RAD tool calls this to paint the actual value of the property.
The Graphics context will have the same current font, color, etc. as the
parent Container. You may safely change the font, color, etc. and not
change them back.
This method should do a silent no-op if isPaintable() is false.
g - the Graphics context to paint onbounds - the rectangle you have reserved to work in
setAsText
public void setAsText(String text)
throws IllegalArgumentExceptionSet the value of this property using a String.
Whether or not this PropertyEditor is editing a String type, this converts
the String into the type of the PropertyEditor.
text - the text to set it to.
setValue
public void setValue(Object value)
Called by the RAD tool to set the value of this property for the PropertyEditor.
If the property type is native, it should be wrapped in the appropriate
wrapper type.
value - the value to set this property to.
supportsCustomEditor
public boolean supportsCustomEditor()
The RAD tool calls this to find out whether the PropertyEditor supports a custom component to edit and display itself.
- true if getCustomEditor() will return a component, false if not.
java.beans.PropertyEditor
Copyright (C) 1998 Free Software Foundation, Inc.
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