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This class encapsulates scrolling.
Introduction
This class encapsulates scrolling.
You can use scrollers (Scroller or OverScroller) to collect the data you need to produce a scrolling animation—for example, in response to a fling gesture.
Scrollers track scroll offsets for you over time, but they don't automatically apply those positions to your view.
See Also
Scroller - Android SDK | Android DevelopersScroller的方法startScroll、fling、computeScrollOffset_scroller.startscroll-CSDN博客Is an Instagram ‘like’ micro-cheating? Gen Z embraces digital sleuthing.Daily Briefing: 'Twas the morning of the debateIt's your responsibility to get and apply new coordinates at a rate that will make the scrolling animation look smooth.
Here is a simple example:
private Scroller mScroller = new Scroller(context); ... public void zoomIn() { // Revert any animation currently in progress mScroller.forceFinished(true); // Start scrolling by providing a starting point and // the distance to travel mScroller.startScroll(0, 0, 100, 0); // Invalidate to request a redraw invalidate(); }
To track the changing positions of the x/y coordinates, use #computeScrollOffset.
The method returns a boolean to indicate whether the scroller is finished.
If it isn't, it means that a fling or programmatic pan operation is still in progress.
You can use this method to find the current offsets of the x and y coordinates, for example:
if (mScroller.computeScrollOffset()) { // Get current x and y positions int currX = mScroller.getCurrX(); int currY = mScroller.getCurrY(); ...}
Example
The following code shows how to use Scroller from android.widget.
Example 1
import android.app.Activity;import android.content.Context;import android.util.AttributeSet;import android.view.MotionEvent;import android.view.View;import android.view.ViewConfiguration;import android.view.animation.DecelerateInterpolator;import android.widget.Scroller;public class SwipeBackView extends View { public interface SwipeBackListener { void onSwipeBack(); }// ww w . de m o 2 s . c o m private SwipeBackListener swipeBackListener; public void setSwipeBackListener(SwipeBackListener swipeBackListener) { this.swipeBackListener = swipeBackListener; } /////////////////////////////////////////// private View rootView; private int touchSlop; private Scroller scroller; private boolean startScroll = false; private float lastX; public SwipeBackView(Context context) { super(context); init(context); } public SwipeBackView(Context context, AttributeSet attrs) { super(context, attrs); init(context); } private void init(Context context) { final Activity activity = (Activity) context; rootView = activity.getWindow().getDecorView(); touchSlop = ViewConfiguration.get(context).getScaledTouchSlop(); scroller = new Scroller(context, new DecelerateInterpolator()); swipeBackListener = new SwipeBackListener() { @Override public void onSwipeBack() { activity.finish(); activity.overridePendingTransition(R.anim.nothing, R.anim.out_slide_to_right); } }; } @Override public boolean onTouchEvent(MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: lastX = event.getRawX(); return true; case MotionEvent.ACTION_MOVE: float curX = event.getRawX(); int delta = (int) (curX - lastX); if (delta > touchSlop && !startScroll) { startScroll = true; } if (startScroll && rootView.getScrollX() - delta <= 0) { rootView.scrollBy(-delta, 0); lastX = curX; } break; case MotionEvent.ACTION_UP: startScroll = false; if (-rootView.getScrollX() > rootView.getWidth() / 3) { if (swipeBackListener != null) { swipeBackListener.onSwipeBack(); } } else { scroller.startScroll(rootView.getScrollX(), 0, -rootView.getScrollX(), 0); invalidate(); } break; default: break; } return super.onTouchEvent(event); } @Override public void computeScroll() { if (scroller.computeScrollOffset()) { rootView.scrollTo(scroller.getCurrX(), scroller.getCurrY()); invalidate(); } }}
Example 2
import android.content.Context;import android.graphics.Bitmap;import android.graphics.BitmapShader;import android.graphics.Canvas;import android.graphics.Matrix;import android.graphics.Shader;import android.graphics.drawable.Drawable;import android.util.AttributeSet;import android.view.animation.LinearInterpolator;import android.widget.Scroller;import android.widget.TextView;public class TitanicTextViewEx extends TextView { private Scroller mScroller; private Drawable wave; private BitmapShader mShader; // shader matrix private Matrix shaderMatrix; private int width; private int height; boolean up = false; private boolean running = false; public TitanicTextViewEx(Context context) { super(context); init();// w w w . d e m o2 s . c o m } public TitanicTextViewEx(Context context, AttributeSet attrs) { super(context, attrs); init(); } public TitanicTextViewEx(Context context, AttributeSet attrs, int defStyleAttr) { super(context, attrs, defStyleAttr); init(); } private void init() { mScroller = new Scroller(this.getContext(), new LinearInterpolator()); shaderMatrix = new Matrix(); } public void start() { running = true; invalidate(); } @Override public void computeScroll() { if (running) { if (mScroller.computeScrollOffset()) { shaderMatrix.setTranslate(mScroller.getCurrX(), mScroller.getCurrY()); invalidate(); } else { if (height != 0) { if (up) { mScroller.startScroll(0, -height / 2, 10 * width, height, 10000); up = false; } else { mScroller.startScroll(0, height / 2, 10 * width, -height, 10000); up = true; } } else { shaderMatrix.setTranslate(0, height / 2); } invalidate(); } } } private void createShalder() { if (wave == null) { wave = getResources().getDrawable(R.drawable.wave); } width = wave.getIntrinsicWidth(); height = this.getHeight(); Bitmap b = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888); wave.setBounds(0, 0, width, height); Canvas c = new Canvas(b); c.drawColor(getCurrentTextColor()); wave.draw(c); mShader = new BitmapShader(b, Shader.TileMode.REPEAT, Shader.TileMode.CLAMP); shaderMatrix.setTranslate(0, height / 2); } @Override public void draw(Canvas canvas) { if (running) { if (mShader == null) { createShalder(); } mShader.setLocalMatrix(shaderMatrix); this.getPaint().setShader(mShader); } super.draw(canvas); }}
Example 3
import android.content.Context;import android.content.res.TypedArray;import android.graphics.Canvas;import android.graphics.Paint;import android.graphics.drawable.Drawable;import android.util.AttributeSet;import android.view.View;import android.view.animation.Interpolator;import android.widget.Scroller;/**/* w w w . d e m o2 s . c o m*/ * TODO: document your custom view class. */public class TabSliderView extends View { private int color; private float lineHeight; private Paint paint; private int position = 0; private Scroller scroller; private int tabCount = 0; int contentWidth = 0; int prevNotifyPosition = -1; public interface OnMoveEndListener { void onMoveEnd(int position); } private OnMoveEndListener listener; public void setOnMoveEnd(OnMoveEndListener l) { listener = l; } public void setTabCount(int tabCount) { this.tabCount = tabCount; } public void setPosition(final int position) { if (this.position != position) { this.position = position; int dx = contentWidth * position / tabCount - scroller.getCurrX(); scroller.startScroll(scroller.getCurrX(), 0, dx, 0, 400); invalidate(); } } private Drawable indicator; public TabSliderView(Context context) { super(context); init(null, 0); } public TabSliderView(Context context, AttributeSet attrs) { super(context, attrs); init(attrs, 0); } public TabSliderView(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); init(attrs, defStyle); } private void init(AttributeSet attrs, int defStyle) { // Load attributes final TypedArray a = getContext().obtainStyledAttributes(attrs, R.styleable.TabSliderView, defStyle, 0); if (a.hasValue(R.styleable.TabSliderView_indicator)) { indicator = a.getDrawable(R.styleable.TabSliderView_indicator); indicator.setCallback(this); color = a.getColor(R.styleable.TabSliderView_barColor, 0x0); lineHeight = a.getDimension(R.styleable.TabSliderView_lineHeight, 0); } a.recycle(); paint = new Paint(); paint.setColor(color); scroller = new Scroller(getContext(), new Interpolator() { private float s = 1.70158f; public float getInterpolation(float t) { return calculate(t, 0, 1, 1); } public Float calculate(float t, float b, float c, float d) { return c * ((t = t / d - 1) * t * ((s + 1) * t + s) + 1) + b; } }); } public void setInterpolator(Interpolator interpolator) { scroller = new Scroller(getContext(), interpolator); } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); if (tabCount == 0) { return; } int paddingLeft = getPaddingLeft(); int paddingTop = getPaddingTop(); int paddingRight = getPaddingRight(); int paddingBottom = getPaddingBottom(); contentWidth = getWidth() - paddingLeft - paddingRight; int contentHeight = getHeight() - paddingTop - paddingBottom; if (indicator != null) { int bgWidth = contentWidth / tabCount; indicator.setBounds(scroller.getCurrX() + paddingLeft - bgWidth / 10, paddingTop, scroller.getCurrX() + paddingLeft + bgWidth + bgWidth / 10, paddingTop + contentHeight - (int) lineHeight); indicator.draw(canvas); } canvas.drawRect(paddingLeft, paddingTop + contentHeight - lineHeight, paddingLeft + contentWidth, paddingTop + contentHeight, paint); if (scroller.computeScrollOffset()) { invalidate(); } else { if (prevNotifyPosition != position) { if (listener != null) { prevNotifyPosition = position; listener.onMoveEnd(position); } } } }}
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Related
- Android Scroller isFinished()
- Android Scroller Scroller(Context context)
- Android Scroller Scroller(Context context, Interpolator interpolator)
- Android Scroller tutorial with examples
- Android android.widget ScrollView
- Android ScrollView addOnLayoutChangeListener(OnLayoutChangeListener listener)
- Android ScrollView addView(View child)
