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      1 /*
      2  * Copyright (C) 2013 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 
     17 package android.content;
     18 
     19 import android.os.Parcel;
     20 import android.os.Parcelable;
     21 
     22 /**
     23  * A single undoable operation.  You must subclass this to implement the state
     24  * and behavior for your operation.  Instances of this class are placed and
     25  * managed in an {@link UndoManager}.
     26  *
     27  * @hide
     28  */
     29 public abstract class UndoOperation<DATA> implements Parcelable {
     30     UndoOwner mOwner;
     31 
     32     /**
     33      * Create a new instance of the operation.
     34      * @param owner Who owns the data being modified by this undo state; must be
     35      * returned by {@link UndoManager#getOwner(String, Object) UndoManager.getOwner}.
     36      */
     37     public UndoOperation(UndoOwner owner) {
     38         mOwner = owner;
     39     }
     40 
     41     /**
     42      * Construct from a Parcel.
     43      */
     44     protected UndoOperation(Parcel src, ClassLoader loader) {
     45     }
     46 
     47     /**
     48      * Owning object as given to {@link #UndoOperation(UndoOwner)}.
     49      */
     50     public UndoOwner getOwner() {
     51         return mOwner;
     52     }
     53 
     54     /**
     55      * Synonym for {@link #getOwner()}.{@link android.content.UndoOwner#getData()}.
     56      */
     57     public DATA getOwnerData() {
     58         return (DATA)mOwner.getData();
     59     }
     60 
     61     /**
     62      * Return true if this undo operation is a member of the given owner.
     63      * The default implementation is <code>owner == getOwner()</code>.  You
     64      * can override this to provide more sophisticated dependencies between
     65      * owners.
     66      */
     67     public boolean matchOwner(UndoOwner owner) {
     68         return owner == getOwner();
     69     }
     70 
     71     /**
     72      * Return true if this operation actually contains modification data.  The
     73      * default implementation always returns true.  If you return false, the
     74      * operation will be dropped when the final undo state is being built.
     75      */
     76     public boolean hasData() {
     77         return true;
     78     }
     79 
     80     /**
     81      * Return true if this operation can be merged with a later operation.
     82      * The default implementation always returns true.
     83      */
     84     public boolean allowMerge() {
     85         return true;
     86     }
     87 
     88     /**
     89      * Called when this undo state is being committed to the undo stack.
     90      * The implementation should perform the initial edits and save any state that
     91      * may be needed to undo them.
     92      */
     93     public abstract void commit();
     94 
     95     /**
     96      * Called when this undo state is being popped off the undo stack (in to
     97      * the temporary redo stack).  The implementation should remove the original
     98      * edits and thus restore the target object to its prior value.
     99      */
    100     public abstract void undo();
    101 
    102     /**
    103      * Called when this undo state is being pushed back from the transient
    104      * redo stack to the main undo stack.  The implementation should re-apply
    105      * the edits that were previously removed by {@link #undo}.
    106      */
    107     public abstract void redo();
    108 
    109     public int describeContents() {
    110         return 0;
    111     }
    112 }
    113