仿 MIUI 弹性拉伸 view ，支持RecyclerView, ListView, GridView, ScrollView ...

首先申明：这个库是基于 Over-Scroll

---

Elasticity 支持 Android 原生控件 RecyclerView, ListView, GridView, ScrollView …

这个库可以让几乎所有的 Android View 具有类似 MIUI 系统里面的一个弹性拉伸的效果。具体的效果可以参考下面的动图。

源码
demo apk

Gradle 依赖

在你的项目的 build.gradle 文件添加如下内容:

allprojects {
    repositories {
        ...
        maven { url "https://jitpack.io" }
    }
}

在你的 module 的 build.gradle 文件中添加如下内容:

dependencies {
    // ...

    compile 'com.github.XanderWang:elasticity:1.0.0'
}

使用

RecyclerView

支持线性和瀑布流的 layout managers，可以很容易接入。实例接入代码如下：

RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);

// Horizontal
ElasticityHelper.setUpOverScroll(recyclerView, ORIENTATION.HORIZONTAL);
// Vertical
ElasticityHelper.setUpOverScroll(recyclerView, ORIENTATION.VERTICAL);

RecyclerView items 的 swiping / dragging 支持

查看 高级用法 .

ListView

ListView listView = (ListView) findViewById(R.id.list_view);
ElasticityHelper.setUpOverScroll(listView);

GridView

GridView gridView = (GridView) findViewById(R.id.grid_view);
ElasticityHelper.setUpOverScroll(gridView);

ViewPager

ViewPager viewPager = (ViewPager) findViewById(R.id.view_pager);
ElasticityHelper.setUpOverScroll(viewPager);

ScrollView, HorizontalScrollView

ScrollView scrollView = (ScrollView) findViewById(R.id.scroll_view);
ElasticityHelper.setUpOverScroll(scrollView);

HorizontalScrollView horizontalScrollView = (HorizontalScrollView) findViewById(R.id.horizontal_scroll_view);
ElasticityHelper.setUpOverScroll(horizontalScrollView);

任何 View - Text, Image… (可以认为一开始就是 Over-Scroll 状态)

View view = findViewById(R.id.demo_view);

// Horizontal
ElasticityHelper.setUpStaticOverScroll(view, ORIENTATION.HORIZONTAL);
// Vertical
ElasticityHelper.setUpStaticOverScroll(view, ORIENTATION.VERTICAL);

高级用法

// Horizontal RecyclerView
RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
new HorizontalElasticityBounceEffect(new RecyclerViewElasticityAdapter(recyclerView));

// ListView (vertical)
ListView listView = (ListView) findViewById(R.id.list_view);
new VerticalElasticityBounceEffect(new AbsListViewElasticityAdapter(listView));

// GridView (vertical)
GridView gridView = (GridView) findViewById(R.id.grid_view);
new VerticalElasticityBounceEffect(new AbsListViewElasticityAdapter(gridView));

// ViewPager
ViewPager viewPager = (ViewPager) findViewById(R.id.view_pager);
new HorizontalElasticityBounceEffect(new ViewPagerElasticityAdapter(viewPager));

// A simple TextView - horizontal
View textView = findViewById(R.id.title);
new HorizontalElasticityBounceEffect(new StaticElasticityAdapter(view));

RecyclerView 借助 ItemTouchHelper 实现 item swiping / dragging

理论上可以很好的支持 item swiping / dragging (based on ItemTouchHelper)， 但是还是建议按如下代码使用。

// Normally you would attach an ItemTouchHelper & a callback to a RecyclerView, this way:
RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
ItemTouchHelper.Callback myCallback = new ItemTouchHelper.Callback() {
    ...
};
ItemTouchHelper myHelper = new ItemTouchHelper(myCallback);
myHelper.attachToRecyclerView(recyclerView);

// INSTEAD of attaching the helper yourself, simply use the dedicated adapter c'tor, e.g.:
new VerticalElasticityBounceEffect(new RecyclerViewElasticityAdapter(recyclerView, myCallback));

查看更多的 swiping / dragging 原理, 可以参考 this useful tutorial.

Over-Scroll Listeners

提供 2 种监听的方式来获取滚动过程中的状态，具体如下

State-Change Listener

状态改变监听，通过这个监听回调，你可以知道状态的改变，使用范例如下：

// Note: over-scroll is set-up using the helper method.
IElasticity elasticity = ElasticityHelper.setUpOverScroll(recyclerView, ORIENTATION.HORIZONTAL);

elasticity.setOverScrollStateListener(new IElasticityStateListener() {
    @Override
    public void onOverScrollStateChange(IElasticity elasticity, int oldState, int newState) {
        switch (newState) {
            case STATE_IDLE:
                // No over-scroll is in effect.
                break;
            case STATE_DRAG_START_SIDE:
                // Dragging started at the left-end.
                break;
            case STATE_DRAG_END_SIDE:
                // Dragging started at the right-end.
                break;
            case STATE_BOUNCE_BACK:
                if (oldState == STATE_DRAG_START_SIDE) {
                    // Dragging stopped -- view is starting to bounce back from the *left-end* onto natural position.
                } else { // i.e. (oldState == STATE_DRAG_END_SIDE)
                    // View is starting to bounce back from the *right-end*.
                }
                break;
        }
    }
}

Real-time Updates Listener

滑动过程监听，可以监听滑动过程中手势的具体变化。

// Note: over-scroll is set-up by explicity instantiating a decorator rather than using the helper; The two methods can be used interchangeably for registering listeners.
IElasticity elasticity = new VerticalElasticityBounceEffect(new RecyclerViewElasticityAdapter(recyclerView, itemTouchHelperCallback));

elasticity.setOverScrollUpdateListener(new IElasticityUpdateListener() {
    @Override
    public void onOverScrollUpdate(IElasticity elasticity, int state, float offset) {
        final View view = elasticity.getView();
        if (offset > 0) {
            // 'view' is currently being over-scrolled from the top.
        } else if (offset < 0) {
            // 'view' is currently being over-scrolled from the bottom.
        } else {
            // No over-scroll is in-effect.
            // This is synonymous with having (state == STATE_IDLE).
        }
    }
});

这两个监听可以单独使用，也可以同时使用，具体看你的需求。

自定义 Views

public class CustomView extends View {
    // ...
}

final CustomView view = (CustomView) findViewById(R.id.custom_view);
new VerticalElasticityBounceEffect(new IElasticityAdapter() {

    @Override
    public View getView() {
        return view;
    }

    @Override
    public boolean isInAbsoluteStart() {
        // canScrollUp() is an example of a method you must implement
        return !view.canScrollUp();
    }

    @Override
    public boolean isInAbsoluteEnd() {
         // canScrollDown() is an example of a method you must implement
        return !view.canScrollDown();
    }
});

完全自定义

/// Make over-scroll applied over a list-view feel more 'stiff'
new VerticalElasticityBounceEffect(new AbsListViewElasticityAdapter(view),
        5f, // Default is 3
        VerticalElasticityBounceEffect.DEFAULT_TOUCH_DRAG_MOVE_RATIO_BCK,
        VerticalElasticityBounceEffect.DEFAULT_DECELERATE_FACTOR,
        VerticalElasticityBounceEffect.MAX_SCALE_FACTOR);

// Make over-scroll applied over a list-view bounce-back more softly
new VerticalElasticityBounceEffect(new AbsListViewElasticityAdapter(view),
        VerticalElasticityBounceEffect.DEFAULT_TOUCH_DRAG_MOVE_RATIO_FWD,
        VerticalElasticityBounceEffect.DEFAULT_TOUCH_DRAG_MOVE_RATIO_BCK,
        -1f // Default is -2,
        VerticalElasticityBounceEffect.MAX_SCALE_FACTOR);