Android侧边栏滑动切换的view效果

 import android.content.Context; import android.graphics.Canvas; import android.graphics.Paint; import android.graphics.drawable.BitmapDrawable; import android.util.AttributeSet; import android.view.MotionEvent; import android.view.View; public class SideBar extends View { private static final int MARGIN_BOTTOM = 2; private int mItemHeight = 18; private OnLetterTouchListener mOnLetterTouchListener; private Paint mPaint; private float mWidthCenter; private int backgroundColor = 0x00F0F0F0; private char[] chars = AppCommon.INDEXER_CHARS; public interface OnLetterTouchListener { public abstract void onPressedDown(int index, char ch); public abstract void onPressedUp(int index, char ch); } public SideBar(Context context) { this(context, null); } public SideBar(Context context, AttributeSet attrs) { this(context, attrs, -1); } public SideBar(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); init(); } private int startY = 0;//其实位置的y轴坐标 public SideBar setChars(char[] chars) { this.chars = chars; //   for(int i = 0 ; i <(26 - chars.length) / 2 ; i++){ //     startY += i * mItemHeight; //   } init(); postInvalidate(); return this; } private void init() { mPaint = new Paint(); mPaint.setColor(0xFFCFCFD0); mPaint.setAntiAlias(true); mPaint.setFakeBoldText(true); mPaint.setTextSize(32); mPaint.setColor(getResources().getColor(R.color.blue)); mPaint.setSubpixelText(true); mPaint.setTextAlign(Paint.Align.CENTER); setBackgroundColor(backgroundColor); } public boolean onTouchEvent(MotionEvent event) { super.onTouchEvent(event); int idx = (int) event.getY() / mItemHeight; if (idx >= chars.length) { idx = chars.length - 1; } else if (idx <0) { idx = 0; } if (event.getAction() == MotionEvent.ACTION_DOWN || event.getAction() == MotionEvent.ACTION_MOVE) { setBackgroundResource(R.color.sidebar_select_background); if (mOnLetterTouchListener != null) { mOnLetterTouchListener.onPressedDown(idx, chars[idx]); } } else if (event.getAction() == MotionEvent.ACTION_UP) { setBackgroundDrawable(new BitmapDrawable()); setBackgroundColor(backgroundColor); if (mOnLetterTouchListener != null) { mOnLetterTouchListener.onPressedUp(idx, chars[idx]); } } return true; } @Override protected void onSizeChanged(int w, int h, int oldw, int oldh) { mItemHeight = (h - MARGIN_BOTTOM) / 26; mWidthCenter = getMeasuredWidth() / 2; super.onSizeChanged(w, h, oldw, oldh); } protected void onDraw(Canvas canvas) { for (int i = 0; i