Home | History | Annotate | Download | only in content 
      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.annotation.UnsupportedAppUsage;
     20 import android.os.Parcel;
     21 import android.os.Parcelable;
     22 
     23 /**
     24  * A single undoable operation.  You must subclass this to implement the state
     25  * and behavior for your operation.  Instances of this class are placed and
     26  * managed in an {@link UndoManager}.
     27  *
     28  * @hide
     29  */
     30 public abstract class UndoOperation<DATA> implements Parcelable {
     31     UndoOwner mOwner;
     32 
     33     /**
     34      * Create a new instance of the operation.
     35      * @param owner Who owns the data being modified by this undo state; must be
     36      * returned by {@link UndoManager#getOwner(String, Object) UndoManager.getOwner}.
     37      */
     38     @UnsupportedAppUsage
     39     public UndoOperation(UndoOwner owner) {
     40         mOwner = owner;
     41     }
     42 
     43     /**
     44      * Construct from a Parcel.
     45      */
     46     @UnsupportedAppUsage
     47     protected UndoOperation(Parcel src, ClassLoader loader) {
     48     }
     49 
     50     /**
     51      * Owning object as given to {@link #UndoOperation(UndoOwner)}.
     52      */
     53     public UndoOwner getOwner() {
     54         return mOwner;
     55     }
     56 
     57     /**
     58      * Synonym for {@link #getOwner()}.{@link android.content.UndoOwner#getData()}.
     59      */
     60     public DATA getOwnerData() {
     61         return (DATA)mOwner.getData();
     62     }
     63 
     64     /**
     65      * Return true if this undo operation is a member of the given owner.
     66      * The default implementation is <code>owner == getOwner()</code>.  You
     67      * can override this to provide more sophisticated dependencies between
     68      * owners.
     69      */
     70     public boolean matchOwner(UndoOwner owner) {
     71         return owner == getOwner();
     72     }
     73 
     74     /**
     75      * Return true if this operation actually contains modification data.  The
     76      * default implementation always returns true.  If you return false, the
     77      * operation will be dropped when the final undo state is being built.
     78      */
     79     public boolean hasData() {
     80         return true;
     81     }
     82 
     83     /**
     84      * Return true if this operation can be merged with a later operation.
     85      * The default implementation always returns true.
     86      */
     87     public boolean allowMerge() {
     88         return true;
     89     }
     90 
     91     /**
     92      * Called when this undo state is being committed to the undo stack.
     93      * The implementation should perform the initial edits and save any state that
     94      * may be needed to undo them.
     95      */
     96     public abstract void commit();
     97 
     98     /**
     99      * Called when this undo state is being popped off the undo stack (in to
    100      * the temporary redo stack).  The implementation should remove the original
    101      * edits and thus restore the target object to its prior value.
    102      */
    103     public abstract void undo();
    104 
    105     /**
    106      * Called when this undo state is being pushed back from the transient
    107      * redo stack to the main undo stack.  The implementation should re-apply
    108      * the edits that were previously removed by {@link #undo}.
    109      */
    110     public abstract void redo();
    111 
    112     public int describeContents() {
    113         return 0;
    114     }
    115 }
    116