AutoScrollBackLayout

在ListView，GridView，RecyclerView列表滚动向底部一段距离，就自动显示一个返回顶部的按钮

效果

使用

1、添加依赖：

compile ('com.gaoneng.library:autoscrollbacklayout:1.1.1'){
        exclude group: 'com.android.support', module: 'recyclerview-v7'
    }

2、通过xml文件添加如下：

<?xml version="1.0" encoding="utf-8"?>
<com.gaoneng.library.AutoScrollBackLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/scroll_layout"
    android:layoutwidth="matchparent"
    android:layoutheight="matchparent"
    android:orientation="vertical"
    android:paddingLeft="8dp"
    android:paddingRight="8dp"
    app:show_scroll="true">
<ListView         android:id="@android:id/list"         android:layoutwidth="matchparent"         android:layoutheight="matchparent"         android:layout_weight="1"         android:drawSelector /> </com.gaoneng.library.AutoScrollBackLayout>

3、调用bindScrollBack()：

AutoScrollBackLayout autoScrollBackLayout = (AutoScrollBackLayout) findViewById(R.id.scroll_layout); ListView listView = (ListView) findViewById(android.R.id.list); List<String> list = new ArrayList<>(); for (int i = 0; i < 20; i++) {     list.add("this is a test! in " + i); } listView.setAdapter(new ArrayAdapter<>(this, android.R.layout.simplelistitem_1, list)); autoScrollBackLayout.bindScrollBack();

原理

• 针对ListView和GridView,通过反射和动态代理的方式监听OnScrollListener，这样就不会影响已有的OnScrollListener的正常运行。

**但是这里需要注意的是，如果已经使用AbsListView.setOnScrollListener()设置过监听， 一定要在其后面调用autoScrollBackLayout.bindScrollBack()**

private void hookScrollListenerForListview() {         try {             //通过反射获取mOnScrollListener对象             Field scrollListenerField = AbsListView.class.getDeclaredField("mOnScrollListener");             scrollListenerField.setAccessible(true);             Object object = scrollListenerField.get(wrapView);             //需要被代理的目前对象             AbsListView.OnScrollListener target;             if (object == null) {                 //如果mOnScrollListener没有设置过，就设置一个空的用来hook                 target = new FakeScrollLitener();             } else {                 target = (AbsListView.OnScrollListener) object;             }             //InvocationHandler对象，用于添加额外的控制处理             ScrollListenerInvocationHandler listenerInvocationHandler = new ScrollListenerInvocationHandler(target);             //Proxy.newProxyInstance生成动态代理对象             AbsListView.OnScrollListener proxy = listenerInvocationHandler.getProxy();             if (DEBUG) {                 Log.i(TAG, "target=" + target.getClass().getName() + " ,proxy=" + proxy.getClass().getName() + ", proxied interfaces=" + Arrays.toString(proxy.getClass().getInterfaces()));             }             //将代理对象proxy设置到被反射的mOnScrollListener的字段中             scrollListenerField.set(wrapView, proxy);         } catch (Exception e) {             Log.e(TAG, e.toString());         }     }

• 针对RecyclerView，因为其内部的监听已经是List<OnScrollListener>形式，所以直接addOnScrollListener()方式添加即可；

private void addScrollListenerForRecyclerView() {         ((RecyclerView) wrapView).addOnScrollListener(new RecyclerView.OnScrollListener() {             @Override             public void onScrollStateChanged(RecyclerView recyclerView, int newState) {                 if (myScrollLitener != null)                     myScrollLitener.onScrollStateChanged(recyclerView, newState);             }

@Override             public void onScrolled(RecyclerView recyclerView, int dx, int dy) {                 if (myScrollLitener != null) myScrollLitener.onScroll(recyclerView, dy, 0, 0);             }         });     }

其他属性

attrs | value ------------ | ------------- app:show_scroll | true/false 是否自动显示返回按钮，默认true app:scroll_distance | dp 触发显示返回按钮的滚动距离，默认100dp app:showanimation | anim 按钮出现动画，默认 R.anim.fabscale_up app:hideanimation | anim 按钮出现动画，默认 R.anim.fabscale_down app:autoarrowicon | drawable 按钮图标，默认 R.drawable.go_top app:scrollgravity | Gravity 按钮的位置，默认 Gravity.BOTTOM and Gravity.CENTERHORIZONTAL