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      1 /*
      2  * Copyright (C) 2015 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 package com.android.messaging.datamodel.binding;
     17 
     18 /**
     19  * The binding class keeps track of a binding between a ui component and an item of BindableData
     20  * It allows each side to ensure that when it communicates with the other they are still bound
     21  * together.
     22  * NOTE: Ensure that the UI component uses the same binding instance for it's whole lifetime
     23  *  (DO NOT CREATE A NEW BINDING EACH TIME A NEW PIECE OF DATA IS BOUND)...
     24  *
     25  * The ui component owns the binding instance.
     26  * It can use it [isBound(data)] to see if the binding still binds to the right piece of data
     27  *
     28  * Upon binding the data is informed of a unique binding key generated in this class and can use
     29  * that to ensure that it is still issuing callbacks to the right piece of ui.
     30  */
     31 public abstract class BindingBase<T extends BindableData> {
     32     /**
     33      * Creates a new exclusively owned binding for the owner object.
     34      */
     35     public static <T extends BindableData> Binding<T> createBinding(final Object owner) {
     36         return new Binding<T>(owner);
     37     }
     38 
     39     /**
     40      * Creates a new read-only binding referencing the source binding object.
     41      * TODO: We may want to refcount the Binding references, so that when the binding owner
     42      * calls unbind() when there's still outstanding references we can catch it.
     43      */
     44     public static <T extends BindableData> ImmutableBindingRef<T> createBindingReference(
     45             final BindingBase<T> srcBinding) {
     46         return new ImmutableBindingRef<T>(srcBinding);
     47     }
     48 
     49     /**
     50      * Creates a detachable binding for the owner object. Use this if your owner object is a UI
     51      * component that may undergo a "detached from window" -> "re-attached to window" transition.
     52      */
     53     public static <T extends BindableData> DetachableBinding<T> createDetachableBinding(
     54             final Object owner) {
     55         return new DetachableBinding<T>(owner);
     56     }
     57 
     58     public abstract T getData();
     59 
     60     /**
     61      * Check if binding connects to the specified data instance
     62      */
     63     public abstract boolean isBound();
     64 
     65     /**
     66      * Check if binding connects to the specified data instance
     67      */
     68     public abstract boolean isBound(final T data);
     69 
     70     /**
     71      * Throw if binding connects to the specified data instance
     72      */
     73     public abstract void ensureBound();
     74 
     75     /**
     76      * Throw if binding connects to the specified data instance
     77      */
     78     public abstract void ensureBound(final T data);
     79 
     80     /**
     81      * Return the binding id for this binding (will be null if not bound)
     82      */
     83     public abstract String getBindingId();
     84 }
     85