我有一个由工作线程管理的自定义SurfaceView。我使用的代码非常类似于以下博客文章中的代码来管理SurfaceView：
http://android-coding.blogspot.com/2011/05/drawing-on-surfaceview.html
我的自定义SurfaceView是可滚动的，因为我会监听触摸事件，将它们发送到手势检测器，并实现onScroll。我会跟踪某些成员变量（x轴和y轴）中的滚动距离，并在绘制到画布时将任何坐标转换为适当的量。我还可以钳制滚动距离，并且可以在夹紧时轻松计算和存储任何过量滚动量。
一切正常。
问题是我想在我的自定义SurfaceView上显示标准的Android过度滚动效果。我尝试手动调用overScrollBy，但它没有工作，我最好的猜测是因为我从工作线程中绘制视图，这意味着视图的onDraw永远不会被调用。
我发现以下有关自定义过卷效果的stackoverflow帖子：
How can I change the OverScroll color in Android 2.3.1?
该帖子不适用于SurfaceViews，但我可能会调整代码。那说，还有更好的方法吗？我想展示其他地方显示的完全相同的过度滚动效果。复制过度滚动的drawables并尝试复制过度滚动逻辑似乎......丑陋。
答案 0 :(得分：4)
好吧，我设法通过使用OverScroller在简单的View中汇总了一个简单的过度滚动示例：
package net.project.experimental;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PointF;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.widget.OverScroller;
public class WorksheetView extends View
{
protected static final int OVERSCROLL_DISTANCE = 10;
protected static final int INVALID_POINTER_ID = -1;
private int fWorksheetWidth = 2000;
private int fWorksheetHeight = 2000;
private OverScroller fScroller;
private VelocityTracker fVelocityTracker = null;
private int fMinimumVelocity;
// The ‘active pointer’ is the one currently moving our object.
private int fTranslatePointerId = INVALID_POINTER_ID;
private PointF fTranslateLastTouch = new PointF( );
private boolean fInteracting = false;
public WorksheetView(Context context, AttributeSet attrs)
{
super( context, attrs );
this.initView( context, attrs );
}
public WorksheetView(Context context, AttributeSet attrs, int defStyle)
{
super( context, attrs, defStyle );
this.initView( context, attrs );
}
protected void initView(Context context, AttributeSet attrs)
{
fScroller = new OverScroller( this.getContext( ) );
this.setOverScrollMode( OVER_SCROLL_ALWAYS );
final ViewConfiguration configuration = ViewConfiguration.get( getContext( ) );
//fTouchSlop = configuration.getScaledTouchSlop( );
fMinimumVelocity = configuration.getScaledMinimumFlingVelocity( );
}
@Override
public boolean onTouchEvent(MotionEvent event)
{
if ( fVelocityTracker == null )
{
fVelocityTracker = VelocityTracker.obtain( );
}
fVelocityTracker.addMovement( event );
final int action = event.getAction( );
switch ( action & MotionEvent.ACTION_MASK )
{
case MotionEvent.ACTION_DOWN:
{
if ( !fScroller.isFinished( ) )
fScroller.abortAnimation( );
final float x = event.getX( );
final float y = event.getY( );
fTranslateLastTouch.set( x, y );
fTranslatePointerId = event.getPointerId( 0 );
this.startInteracting( );
break;
}
case MotionEvent.ACTION_MOVE:
{
final int pointerIndexTranslate = event.findPointerIndex( fTranslatePointerId );
if ( pointerIndexTranslate >= 0 )
{
float translateX = event.getX( pointerIndexTranslate );
float translateY = event.getY( pointerIndexTranslate );
this.overScrollBy(
(int) (fTranslateLastTouch.x - translateX),
(int) (fTranslateLastTouch.y - translateY),
this.getScrollX( ),
this.getScrollY( ),
fWorksheetWidth - this.getWidth( ),
fWorksheetHeight - this.getHeight( ),
OVERSCROLL_DISTANCE,
OVERSCROLL_DISTANCE,
true );
fTranslateLastTouch.set( translateX, translateY );
this.invalidate( );
}
break;
}
case MotionEvent.ACTION_UP:
{
final VelocityTracker velocityTracker = fVelocityTracker;
velocityTracker.computeCurrentVelocity( 1000 );
//velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
int initialXVelocity = (int) velocityTracker.getXVelocity( );
int initialYVelocity = (int) velocityTracker.getYVelocity( );
if ( (Math.abs( initialXVelocity ) + Math.abs( initialYVelocity ) > fMinimumVelocity) )
{
this.fling( -initialXVelocity, -initialYVelocity );
}
else
{
if ( fScroller.springBack( this.getScrollX( ), this.getScrollY( ), 0, fWorksheetWidth - this.getWidth( ), 0, fWorksheetHeight - this.getHeight( ) ) )
this.invalidate( );
this.stopInteracting( );
}
if ( fVelocityTracker != null )
{
fVelocityTracker.recycle( );
fVelocityTracker = null;
}
fTranslatePointerId = INVALID_POINTER_ID;
break;
}
case MotionEvent.ACTION_POINTER_DOWN:
{
break;
}
case MotionEvent.ACTION_POINTER_UP:
{
final int pointerIndex = (event.getAction( ) & MotionEvent.ACTION_POINTER_INDEX_MASK) >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
final int pointerId = event.getPointerId( pointerIndex );
if ( pointerId == fTranslatePointerId )
{
// This was our active pointer going up. Choose a new
// active pointer and adjust accordingly.
final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
fTranslateLastTouch.set( event.getX( newPointerIndex ), event.getY( newPointerIndex ) );
fTranslatePointerId = event.getPointerId( newPointerIndex );
}
break;
}
case MotionEvent.ACTION_CANCEL:
{
if ( fScroller.springBack( this.getScrollX( ), this.getScrollY( ), 0, fWorksheetWidth - this.getWidth( ), 0, fWorksheetHeight - this.getHeight( ) ) )
this.invalidate( );
fTranslatePointerId = INVALID_POINTER_ID;
break;
}
}
return true;
}
private void fling(int velocityX, int velocityY)
{
int x = this.getScrollX( );
int y = this.getScrollY( );
this.startInteracting( );
//fScroller.setFriction( ViewConfiguration.getScrollFriction( ) );
fScroller.fling( x, y, velocityX, velocityY, 0, fWorksheetWidth - this.getWidth( ), 0, fWorksheetHeight - this.getHeight( ) );
this.invalidate( );
}
private void startInteracting()
{
fInteracting = true;
}
private void stopInteracting()
{
fInteracting = false;
}
@Override
public void computeScroll()
{
if ( fScroller != null && fScroller.computeScrollOffset( ) )
{
int oldX = this.getScrollX( );
int oldY = this.getScrollY( );
int x = fScroller.getCurrX( );
int y = fScroller.getCurrY( );
if ( oldX != x || oldY != y )
{
this.overScrollBy(
x - oldX,
y - oldY,
oldX,
oldY,
fWorksheetWidth - this.getWidth( ),
fWorksheetHeight - this.getHeight( ),
OVERSCROLL_DISTANCE,
OVERSCROLL_DISTANCE,
false );
}
if ( fScroller.isFinished( ) )
this.stopInteracting( );
this.postInvalidate( );
}
}
@Override
protected void onOverScrolled(int scrollX, int scrollY, boolean clampedX, boolean clampedY)
{
// Treat animating scrolls differently; see #computeScroll() for why.
if ( !fScroller.isFinished( ) )
{
super.scrollTo( scrollX, scrollY );
if ( clampedX || clampedY )
{
fScroller.springBack( this.getScrollX( ), this.getScrollY( ), 0, fWorksheetWidth - this.getWidth( ), 0, fWorksheetHeight - this.getHeight( ) );
}
}
else
{
super.scrollTo( scrollX, scrollY );
}
awakenScrollBars( );
}
@Override
protected int computeHorizontalScrollExtent()
{
return this.getWidth( );
}
@Override
protected int computeHorizontalScrollRange()
{
return fWorksheetWidth;
}
@Override
protected int computeHorizontalScrollOffset()
{
return this.getScrollX( );
}
@Override
protected int computeVerticalScrollExtent()
{
return this.getHeight( );
}
@Override
protected int computeVerticalScrollRange()
{
return fWorksheetHeight;
}
@Override
protected int computeVerticalScrollOffset()
{
return this.getScrollY( );
}
@Override
protected void onDraw(Canvas canvas)
{
canvas.drawColor( Color.BLACK );
Paint paint = new Paint( );
if ( fInteracting )
;
paint.setColor( Color.WHITE );
canvas.drawRect( 0, 0, fWorksheetWidth, fWorksheetHeight, paint );
paint.setColor( Color.RED );
for (int i = 0; i < 1500; i += 10)
{
canvas.drawLine( i, 0, i + 100, 500, paint );
}
canvas.drawRect( fWorksheetWidth - 50, 0, fWorksheetWidth, fWorksheetHeight, paint );
canvas.drawRect( 0, fWorksheetHeight - 50, fWorksheetWidth, fWorksheetHeight, paint );
}
}
答案 1 :(得分：1)
好的，要真正回答Android风格过度滚动的问题。您可以比我的上一个答案（代码）更进一步使用OverScroller通过绘图实现过度滚动后，您可以限制页面移动，因此页面不会过度滚动。相反，您可以为Android风格的过度滚动绘制资源 - 这就是您所说的“手动”。
请参阅下面的示例，这是我昨天发布的代码的补充。现在，'onDraw'不会让页面在视觉上过度滚动。然后'displatchDraw'将绘制一个可绘制的资源来表示Android风格的过度滚动。
注意，我是一个记忆狂，所以我在所有四个角上使用相同的资源，并在画布上渲染时通过矩阵手动旋转。
private void compensateForOverscroll(Canvas canvas)
{
int x = this.getScrollX( );
int y = this.getScrollY( );
Matrix matrix = canvas.getMatrix( );
int maxX = fWorksheetWidth - this.getWidth( );
int maxY = fWorksheetHeight - this.getHeight( );
if ( x < 0 || x > maxX || y < 0 || y > maxY )
{
if ( x < 0 )
matrix.postTranslate( x, 0 );
else if ( x > maxX )
matrix.postTranslate( (x - maxX), 0 );
if ( y < 0 )
matrix.postTranslate( 0, y );
else if ( y > maxY )
matrix.postTranslate( 0, (y - maxY) );
canvas.setMatrix( matrix );
}
}
@Override
protected void dispatchDraw(Canvas canvas)
{
int width = this.getWidth( );
int height = this.getHeight( );
int maxX = fWorksheetWidth - width;
int maxY = fWorksheetHeight - height;
int x = this.getScrollX( );
int y = this.getScrollY( );
if ( x < 0 || x > maxX )
{
canvas.save( );
Matrix canvasMatrix = canvas.getMatrix( );
if ( x < 0 )
{
fOverScrollDrawable.setBounds( 0, x, height, x - x );
canvasMatrix.preRotate( -90 );
canvasMatrix.preTranslate( - y - height, 0 );
}
else if ( x > maxX )
{
fOverScrollDrawable.setBounds( 0, maxX, height, x );
canvasMatrix.preRotate( 90 );
canvasMatrix.preTranslate( y, - x - fWorksheetWidth );
}
canvas.setMatrix( canvasMatrix );
fOverScrollDrawable.draw( canvas );
canvas.restore( );
}
if ( y < 0 || y > maxY )
{
canvas.save( );
Matrix canvasMatrix = canvas.getMatrix( );
if ( y < 0 )
{
fOverScrollDrawable.setBounds( x, y, x + width, y - y );
}
else if ( y > maxY )
{
fOverScrollDrawable.setBounds( 0, maxY, width, y );
canvasMatrix.preRotate( 180 );
canvasMatrix.preTranslate( - x - width, - y - fWorksheetHeight );
}
canvas.setMatrix( canvasMatrix );
fOverScrollDrawable.draw( canvas );
canvas.restore( );
}
}
@Override
protected void onDraw(Canvas canvas)
{
canvas.save( );
this.compensateForOverscroll( canvas );
canvas.drawColor( Color.BLACK );
Paint paint = new Paint( );
if ( fInteracting )
;
paint.setColor( Color.WHITE );
canvas.drawRect( 0, 0, fWorksheetWidth, fWorksheetHeight, paint );
paint.setColor( Color.RED );
for (int i = 0; i < 1500; i += 10)
{
canvas.drawLine( i, 0, i + 100, 500, paint );
}
canvas.drawRect( fWorksheetWidth - 50, 0, fWorksheetWidth, fWorksheetHeight, paint );
canvas.drawRect( 0, fWorksheetHeight - 50, fWorksheetWidth, fWorksheetHeight, paint );
canvas.restore( );
}
drawable初始化如下：
Drawable fOverScrollDrawable;
...
Resources rsr = context.getResources( );
fOverScrollDrawable = rsr.getDrawable( R.drawable.overscroll_glow );
过度滚动的图像资源发光，我在sdk中拍摄了两张图像，并将它们合并为一个可绘制的资源：
答案 2 :(得分：0)
嗯，我有同样的问题。
我查看了android视图的实现，并在'onOverScrolled'里面只有注释“故意为空”。
看看ListView实现，我可以看到他们通过获取drawables'com.android.internal.R.styleable.ListView_overScrollHeader'和'com.android.internal.R.styleable.ListView_overScrollFooter'手动实现了它。不能从外面使用。不幸的是，我无法在消息来源中找到这些资源。
因为看起来我们不得不手动进行过度滚动......