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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 android.databinding;
     17 
     18 /**
     19  * A listener implemented by all two-way bindings to be notified when a triggering change happens.
     20  * For example, when there is a two-way binding for android:text, an implementation of
     21  * <code>InverseBindingListener</code> will be generated in the layout's binding class.
     22  * <pre>
     23  * private static class InverseListenerTextView implements InverseBindingListener {
     24  *     &commat;Override
     25  *     public void onChange() {
     26  *         mObj.setTextValue(mTextView.getText());
     27  *     }
     28  * }
     29  * </pre>
     30  * <p>
     31  * A {@link BindingAdapter} should be used to assign the event listener.
     32  * For example, <code>android:onTextChanged</code> will need to trigger the event listener
     33  * for the <code>android:text</code> attribute.
     34  * <pre>
     35  * &commat;InverseBindingAdapter(attribute = "android:text", event = "android:textAttrChanged")
     36  * public static void captureTextValue(TextView view, ObservableField&lt;CharSequence> value) {
     37  *     CharSequence newValue = view.getText();
     38  *     CharSequence oldValue = value.get();
     39  *     if (oldValue == null) {
     40  *         value.set(newValue);
     41  *     } else if (!contentEquals(newValue, oldValue)) {
     42  *         value.set(newValue);
     43  *     }
     44  * }
     45  * &commat;BindingAdapter(value = {"android:beforeTextChanged", "android:onTextChanged",
     46  *                          "android:afterTextChanged", "android:textAttrChanged"},
     47  *                          requireAll = false)
     48  * public static void setTextWatcher(TextView view, final BeforeTextChanged before,
     49  *                                   final OnTextChanged on, final AfterTextChanged after,
     50  *                                   final InverseBindingListener textAttrChanged) {
     51  *     TextWatcher newValue = new TextWatcher() {
     52  *         ...
     53  *         &commat;Override
     54  *         public void onTextChanged(CharSequence s, int start, int before, int count) {
     55  *             if (on != null) {
     56  *                 on.onTextChanged(s, start, before, count);
     57  *             }
     58  *             if (textAttrChanged != null) {
     59  *                 textAttrChanged.onChange();
     60  *             }
     61  *         }
     62  *     }
     63  *     TextWatcher oldValue = ListenerUtil.trackListener(view, newValue, R.id.textWatcher);
     64  *     if (oldValue != null) {
     65  *         view.removeTextChangedListener(oldValue);
     66  *     }
     67  *     view.addTextChangedListener(newValue);
     68  * }
     69  * </pre>
     70  */
     71 public interface InverseBindingListener {
     72     /**
     73      * Notifies the data binding system that the attribute value has changed.
     74      */
     75     void onChange();
     76 }
     77