Android官方DataBinding（十）：双向绑定之基于InverseBindingAdapter的反向绑定

小咪咪 2024-02-18 14:54 4阅读 0赞

**Android官方DataBinding（十）：双向绑定之基于InverseBindingAdapter的反向绑定**

我给出一个简单例子，说明如何基于InverseBindingAdapter进行双向绑定中的反向绑定。  
以一个经典的开发需求任务：下拉刷新。一般的下拉刷新，头部出现一个滚动的进度显示（ProgressBar）和一些文字提示，当下拉加载完毕后自动消失。  
我写一个自定义view，继承自NestedScrollView，继承自NestedScrollView主要是为了利用NestedScrollView的下拉滚动事件。在这里面触发下拉刷新事件。  
老规矩，先写一个model：

package zhangphil.test;
    
    import android.databinding.BaseObservable;
    import android.databinding.ObservableBoolean;
    
    /**
     * Created by Phil on 2017/8/25.
     */
    
    public class ViewModel extends BaseObservable {
        public final ObservableBoolean isRefreshing = new ObservableBoolean();
    }

写布局，activity\_main.xml：

<?xml version="1.0" encoding="utf-8"?>
    <layout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto">
    
        <data>
    
            <import type="android.view.View" />
    
            <variable
                name="model"
                type="zhangphil.test.ViewModel" />
        </data>
    
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical">
    
            <ProgressBar
                android:layout_width="100dp"
                android:layout_height="100dp"
                android:layout_gravity="center_horizontal"
                android:visibility="@{model.isRefreshing ? View.VISIBLE:View.GONE}" />
    
            <TextView
                android:layout_width="match_parent"
                android:layout_height="50dp"
                android:background="@android:color/holo_red_light"
                android:gravity="center"
                android:text="加载中..."
                android:visibility="@{model.isRefreshing ? View.VISIBLE:View.GONE}" />
    
            <zhangphil.test.PhilView
                android:id="@+id/philview"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:background="@android:color/holo_blue_light"
                app:refreshing="@={model.isRefreshing}">
    
                <LinearLayout
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:orientation="vertical">
    
                    <TextView
                        android:layout_width="match_parent"
                        android:layout_height="150dp"
                        android:gravity="center"
                        android:text="z" />
    
                    <TextView
                        android:layout_width="match_parent"
                        android:layout_height="150dp"
                        android:gravity="center"
                        android:text="h" />
    
                    <TextView
                        android:layout_width="match_parent"
                        android:layout_height="150dp"
                        android:gravity="center"
                        android:text="a" />
    
                    <TextView
                        android:layout_width="match_parent"
                        android:layout_height="150dp"
                        android:gravity="center"
                        android:text="n" />
    
                    <TextView
                        android:layout_width="match_parent"
                        android:layout_height="150dp"
                        android:gravity="center"
                        android:text="g" />
                </LinearLayout>
    
            </zhangphil.test.PhilView>
        </LinearLayout>
    </layout>

自定义的PhilView.java：

package zhangphil.test;
    
    import android.content.Context;
    import android.databinding.BindingAdapter;
    import android.databinding.InverseBindingAdapter;
    import android.databinding.InverseBindingListener;
    import android.support.v4.widget.NestedScrollView;
    import android.util.AttributeSet;
    import android.util.Log;
    
    /**
     * Created by Phil on 2017/8/25.
     */
    
    public class PhilView extends NestedScrollView {
        private static final String TAG = "调试";
        private static boolean isRefreshing = false;
        private static InverseBindingListener mInverseBindingListener;
    
        public PhilView(Context context, AttributeSet attrs) {
            super(context, attrs);
        }
    
        @BindingAdapter(value = "refreshing", requireAll = false)
        public static void setRefreshing(PhilView view, boolean refreshing) {
            if (isRefreshing == refreshing) {
                //防止死循环
                Log.d(TAG, "重复设置");
                return;
            } else {
                Log.d(TAG, "setRefreshing " + refreshing);
                isRefreshing = refreshing;
            }
        }
    
        @InverseBindingAdapter(attribute = "refreshing", event = "refreshingAttrChanged")
        public static boolean getRefreshing(PhilView view) {
            return isRefreshing;
        }
    
        @BindingAdapter(value = {"refreshingAttrChanged"}, requireAll = false)
        public static void setRefreshingAttrChanged(PhilView view, final InverseBindingListener inverseBindingListener) {
            Log.d(TAG, "setRefreshingAttrChanged");
    
            if (inverseBindingListener == null) {
                view.setRefreshingListener(null);
            } else {
                mInverseBindingListener = inverseBindingListener;
                view.setRefreshingListener(mOnRefreshingListener);
            }
        }
    
        @Override
        protected void onScrollChanged(int x, int y, int oldx, int oldy) {
            super.onScrollChanged(x, y, oldx, oldy);
    
            if ((y < oldy) && y == 0) {
                if (isRefreshing) {
                    Log.d(TAG, "正在刷新，请勿重复加载");
                    return;
                } else {
                    longTimeTask();
                }
            }
        }
    
        public void setRefreshingListener(OnRefreshingListener listener) {
            this.mOnRefreshingListener = listener;
        }
    
        public static abstract class OnRefreshingListener {
            public void startRefreshing() {
                isRefreshing = true;
                mInverseBindingListener.onChange();
            }
    
            public void stopRefreshing() {
                isRefreshing = false;
                mInverseBindingListener.onChange();
            }
        }
    
        private static OnRefreshingListener mOnRefreshingListener = new OnRefreshingListener() {
            @Override
            public void startRefreshing() {
                super.startRefreshing();
            }
    
            @Override
            public void stopRefreshing() {
                super.stopRefreshing();
            }
        };
    
        private void longTimeTask() {
            new Thread(new Runnable() {
                @Override
                public void run() {
                    mOnRefreshingListener.startRefreshing();
    
                    try {
                        //假设这里做了一个长时间的耗时操作
                        Thread.sleep(5000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
    
                    mOnRefreshingListener.stopRefreshing();
                }
            }).start();
        }
    }

测试的MainActivity.java：

package zhangphil.test;
    
    import android.databinding.DataBindingUtil;
    import android.support.v7.app.AppCompatActivity;
    import android.os.Bundle;
    
    import zhangphil.test.databinding.ActivityMainBinding;
    
    public class MainActivity extends AppCompatActivity {
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
    
            ActivityMainBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_main);
    
            ViewModel vm = new ViewModel();
            binding.setModel(vm);
        }
    }

代码运行结果初始化状态：

![Center][]

当下拉时候：

![Center 1][]

注意，代码有些小问题：只有先向上翻滚，再往下拉时候才会触发头部的刷新滚动提醒。然而这不是本文要解决的重点，随后的文章将改进。  
  
  
  
附录：  
1，《Android官方DataBinding简例（一）》链接：http://blog.csdn.net/zhangphil/article/details/77322530  
2，《Android官方DataBinding（二）：动态数据更新notifyPropertyChanged》链接：http://blog.csdn.net/zhangphil/article/details/77328688  
3，《Android官方DataBinding（三）：RecyclerView 使用ViewDataBinding更新数据》链接：http://blog.csdn.net/zhangphil/article/details/77367432  
4，《Android官方DataBinding（四）：BindingAdapter》链接：http://blog.csdn.net/zhangphil/article/details/77374211  
5，《Android官方DataBinding（五）：ObservableMap，ObservableArrayMap》链接：http://blog.csdn.net/zhangphil/article/details/77448933  
6，《Android官方DataBinding（六）： @= 操作符进行双向绑定》链接：http://blog.csdn.net/zhangphil/article/details/77454045  
7，《Android官方DataBinding（七）：BindingMethods与BindingMethod》链接：http://blog.csdn.net/zhangphil/article/details/77479843  
8，《Android官方DataBinding（八）：Lambda长表达式事件处理》链接：http://blog.csdn.net/zhangphil/article/details/77503013  
9，《Android官方DataBinding（九）：反向绑定，View变化结果回写进数据模型中》链接：http://blog.csdn.net/zhangphil/article/details/77649256

[Center]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/29/ffabef977f60473c80ee9f1744fdf589.png
[Center 1]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/29/077d3c2382994363957b76eccde776e4.png