ScrollView的顶部下拉和底部上拉回弹效果
要实现ScrollView的回弹效果，需要对其进行触摸事件处理。先来看一下简单的效果：
根据Android的View事件分发处理机制，下面对dispatchTouchEvent进行详细分析：
在加载布局完成之后，获取ScrollView的第一个子元素，保存它的参数，left top right bottom参数，根据顶部下拉操作和底部上拉操作进行子View的布局参数根据滑动距离改变，ACTION_UP的时候判断是否存在回弹，如果需要则进行动画回弹到原来的位置，可以添加一个回弹结束监听，比如监听回弹处理跳转到其他的页面的操作等。
具体的实现如下，添加了是否禁用顶部和底部回弹的参数设置，以及回弹效果结束监听。
/** * A Simple Rebound ScrollView * @author Denluoyia */ public class ReboundScrollView extends ScrollView{ private boolean mEnableTopRebound = true; private boolean mEnableBottomRebound = true; private OnReboundEndListener mOnReboundEndListener; private View mContentView; private Rect mRect = new Rect(); public ReboundScrollView(Context context) { super(context); } public ReboundScrollView(Context context, AttributeSet attrs) { super(context, attrs); } public ReboundScrollView(Context context, AttributeSet attrs, int defStyleAttr) { super(context, attrs, defStyleAttr); } /** after inflating view, we can get the width and height of view */ @Override protected void onFinishInflate() { super.onFinishInflate(); mContentView = getChildAt(0); } @Override protected void onLayout(boolean changed, int l, int t, int r, int b) { super.onLayout(changed, l, t, r, b); if (mContentView == null) return; // to remember the location of mContentView mRect.set(mContentView.getLeft(), mContentView.getTop(), mContentView.getRight(), mContentView.getBottom()); } public ReboundScrollView setOnReboundEndListener(OnReboundEndListener onReboundEndListener){ this.mOnReboundEndListener = onReboundEndListener; return this; } public ReboundScrollView setEnableTopRebound(boolean enableTopRebound){ this.mEnableTopRebound = enableTopRebound; return this; } public ReboundScrollView setEnableBottomRebound(boolean mEnableBottomRebound){ this.mEnableBottomRebound = mEnableBottomRebound; return this; } private int lastY; private boolean rebound = false; private int reboundDirection = 0; //<0 表示下部回弹 >0 表示上部回弹 0表示不回弹 @Override public boolean dispatchTouchEvent(MotionEvent ev) { if (mContentView == null){ return super.dispatchTouchEvent(ev); } switch (ev.getAction()){ case MotionEvent.ACTION_DOWN: lastY = (int) ev.getY(); break; case MotionEvent.ACTION_MOVE: if (!isScrollToTop() && !isScrollToBottom()){ lastY = (int) ev.getY(); break; } //处于顶部或者底部 int deltaY = (int) (ev.getY() - lastY); //deltaY > 0 下拉 deltaY < 0 上拉 //disable top or bottom rebound if ((!mEnableTopRebound && deltaY > 0) || (!mEnableBottomRebound && deltaY < 0)){ break; } int offset = (int) (deltaY * 0.48); mContentView.layout(mRect.left, mRect.top + offset, mRect.right, mRect.bottom + offset); rebound = true; break; case MotionEvent.ACTION_UP: if (!rebound) break; reboundDirection = mContentView.getTop() - mRect.top; TranslateAnimation animation = new TranslateAnimation(0, 0, mContentView.getTop(), mRect.top); animation.setDuration(300); animation.setAnimationListener(new Animation.AnimationListener() { @Override public void onAnimationStart(Animation animation) { } @Override public void onAnimationEnd(Animation animation) { if (mOnReboundEndListener != null){ if (reboundDirection > 0){ mOnReboundEndListener.onReboundTopComplete(); } if (reboundDirection < 0){ mOnReboundEndListener.onReboundBottomComplete(); } reboundDirection = 0; } } @Override public void onAnimationRepeat(Animation animation) { } }); mContentView.startAnimation(animation); mContentView.layout(mRect.left, mRect.top, mRect.right, mRect.bottom); rebound = false; break; } return super.dispatchTouchEvent(ev); } @Override public void setFillViewport(boolean fillViewport) { super.setFillViewport(true); //默认是填充ScrollView 或者再XML布局文件中设置fillViewport属性 } /** * 判断当前ScrollView是否处于顶部 */ private boolean isScrollToTop(){ return getScrollY() == 0; } /** * 判断当前ScrollView是否已滑到底部 */ private boolean isScrollToBottom(){ return mContentView.getHeight() <= getHeight() + getScrollY(); } /** * listener for top and bottom rebound * do your implement in the following methods */ public interface OnReboundEndListener{ void onReboundTopComplete(); void onReboundBottomComplete(); } }
使用：
直接在XML布局文件中把ScrollView替换成ReboundScrollView就可以了。还可以拓展把回弹顶部和底部添加其他的动画效果（之后再拓展试下）。
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" tools:context=".TestActivity"> <com.denluoyia.dtils.widget.ReboundScrollView android:id="@+id/reboundScrollView" android:layout_width="match_parent" android:layout_height="match_parent"> <LinearLayout android:layout_width="match_parent" android:layout_height="match_parent" android:background="#eefade" android:padding="16dp"> <TextView android:layout_width="match_parent" android:layout_height="match_parent" android:textSize="15sp" android:lineSpacingExtra="5dp" android:text="@string/content"/> </LinearLayout> </com.denluoyia.dtils.widget.ReboundScrollView> </LinearLayout>
如果需要禁用回弹，可以直接设置enableTopRebound和enableBottomRebound参数，同样设置回弹结束（或开始）监听。
public class TestActivity extends AppCompatActivity { private ReboundScrollView reboundScrollView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_test); reboundScrollView = findViewById(R.id.reboundScrollView); //reboundScrollView.setEnableTopRebound(false); //reboundScrollView.setEnableBottomRebound(false); reboundScrollView.setOnReboundEndListener(new ReboundScrollView.OnReboundEndListener() { @Override public void onReboundTopComplete() { Toast.makeText(TestActivity.this, "顶部回弹", Toast.LENGTH_SHORT).show(); } @Override public void onReboundBottomComplete() { Toast.makeText(TestActivity.this, "底部回弹", Toast.LENGTH_SHORT).show(); } }); } }
