/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.util;
/**
* A property is an abstraction that can be used to represent a <emb>mutable</em> value that is held
* in a <em>host</em> object. The Property's {@link #set(Object, Object)} or {@link #get(Object)}
* methods can be implemented in terms of the private fields of the host object, or via "setter" and
* "getter" methods or by some other mechanism, as appropriate.
*
* @param <T> The class on which the property is declared.
* @param <V> The type that this property represents.
*/
public abstract class Property<T, V> {
private final String mName;
private final Class<V> mType;
/**
* This factory method creates and returns a Property given the <code>class</code> and
* <code>name</code> parameters, where the <code>"name"</code> parameter represents either:
* <ul>
* <li>a public <code>getName()</code> method on the class which takes no arguments, plus an
* optional public <code>setName()</code> method which takes a value of the same type
* returned by <code>getName()</code>
* <li>a public <code>isName()</code> method on the class which takes no arguments, plus an
* optional public <code>setName()</code> method which takes a value of the same type
* returned by <code>isName()</code>
* <li>a public <code>name</code> field on the class
* </ul>
*
* <p>If either of the get/is method alternatives is found on the class, but an appropriate
* <code>setName()</code> method is not found, the <code>Property</code> will be
* {@link #isReadOnly() readOnly}. Calling the {@link #set(Object, Object)} method on such
* a property is allowed, but will have no effect.</p>
*
* <p>If neither the methods nor the field are found on the class a
* {@link NoSuchPropertyException} exception will be thrown.</p>
*/
public static <T, V> Property<T, V> of(Class<T> hostType, Class<V> valueType, String name) {
return new ReflectiveProperty<T, V>(hostType, valueType, name);
}
/**
* A constructor that takes an identifying name and {@link #getType() type} for the property.
*/
public Property(Class<V> type, String name) {
mName = name;
mType = type;
}
/**
* Returns true if the {@link #set(Object, Object)} method does not set the value on the target
* object (in which case the {@link #set(Object, Object) set()} method should throw a {@link
* NoSuchPropertyException} exception). This may happen if the Property wraps functionality that
* allows querying the underlying value but not setting it. For example, the {@link #of(Class,
* Class, String)} factory method may return a Property with name "foo" for an object that has
* only a <code>getFoo()</code> or <code>isFoo()</code> method, but no matching
* <code>setFoo()</code> method.
*/
public boolean isReadOnly() {
return false;
}
/**
* Sets the value on <code>object</code> which this property represents. If the method is unable
* to set the value on the target object it will throw an {@link UnsupportedOperationException}
* exception.
*/
public void set(T object, V value) {
throw new UnsupportedOperationException("Property " + getName() +" is read-only");
}
/**
* Returns the current value that this property represents on the given <code>object</code>.
*/
public abstract V get(T object);
/**
* Returns the name for this property.
*/
public String getName() {
return mName;
}
/**
* Returns the type for this property.
*/
public Class<V> getType() {
return mType;
}
}