Android自定义滚动选择器实例代码

package com.linzihui.widget;

import android.annotation.SuppressLint;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Paint.Align;
import android.graphics.Paint.FontMetricsInt;
import android.graphics.Paint.Style;
import android.os.Handler;
import android.os.Message;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;


import java.util.ArrayList;
import java.util.List;
import java.util.Timer;
import java.util.TimerTask;

/**
 * 自定义滚动选择器
 * 
 * @author cuiran
 *
 */
@SuppressLint({ "HandlerLeak", "ClickableViewAccessibility" })
public class PickerScrollView extends View {

  public static final String TAG = "PickerView";
  /**
   * text之间间距和minTextSize之比
   */
  public static final float MARGIN_ALPHA = 2.8f;
  /**
   * 自动回滚到中间的速度
   */
  public static final float SPEED = 2;

  private List<Pickers> mDataList;
  /**
   * 选中的位置，这个位置是mDataList的中心位置，一直不变
   */
  private int mCurrentSelected;
  private Paint mPaint;

  private float mMaxTextSize = 20;
  private float mMinTextSize = 10;

  private float mMaxTextAlpha = 255;
  private float mMinTextAlpha = 120;

  private int mColorText = 0x333333;

  private int mViewHeight;
  private int mViewWidth;

  private float mLastDownY;
  /**
   * 滑动的距离
   */
  private float mMoveLen = 0;
  private boolean isInit = false;
  private onSelectListener mSelectListener;
  private Timer timer;
  private MyTimerTask mTask;

  Handler updateHandler = new Handler() {

    @Override
    public void handleMessage(Message msg) {
      if (Math.abs(mMoveLen) < SPEED) {
        mMoveLen = 0;
        if (mTask != null) {
          mTask.cancel();
          mTask = null;
          performSelect();
        }
      } else
        // 这里mMoveLen / Math.abs(mMoveLen)是为了保有mMoveLen的正负号，以实现上滚或下滚
        mMoveLen = mMoveLen - mMoveLen / Math.abs(mMoveLen) * SPEED;
      invalidate();
    }

  };

  public PickerScrollView(Context context) {
    super(context);
    init();
  }

  public PickerScrollView(Context context, AttributeSet attrs) {
    super(context, attrs);
    init();
  }

  public void setOnSelectListener(onSelectListener listener) {
    mSelectListener = listener;
  }

  private void performSelect() {
    if (mSelectListener != null)
      mSelectListener.onSelect(mDataList.get(mCurrentSelected));
  }

  public void setData(List<Pickers> datas) {
    mDataList = datas;
    mCurrentSelected = datas.size() / 2;
    invalidate();
  }

  /**
   * 选择选中的item的index
   * 
   * @param selected
   */
  public void setSelected(int selected) {
    mCurrentSelected = selected;
    int distance = mDataList.size() / 2 - mCurrentSelected;
    if (distance < 0)
      for (int i = 0; i < -distance; i++) {
        moveHeadToTail();
        mCurrentSelected--;
      }
    else if (distance > 0)
      for (int i = 0; i < distance; i++) {
        moveTailToHead();
        mCurrentSelected++;
      }
    invalidate();
  }

  /**
   * 选择选中的内容
   * 
   * @param mSelectItem
   */
  public void setSelected(String mSelectItem) {
    for (int i = 0; i < mDataList.size(); i++)
      if (mDataList.get(i).equals(mSelectItem)) {
        setSelected(i);
        break;
      }
  }

  private void moveHeadToTail() {
    Pickers head = mDataList.get(0);
    mDataList.remove(0);
    mDataList.add(head);
  }

  private void moveTailToHead() {
    Pickers tail = mDataList.get(mDataList.size() - 1);
    mDataList.remove(mDataList.size() - 1);
    mDataList.add(0, tail);
  }

  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    mViewHeight = getMeasuredHeight();
    mViewWidth = getMeasuredWidth();
    // 按照View的高度计算字体大小
    mMaxTextSize = mViewHeight / 8.0f;
    mMinTextSize = mMaxTextSize / 2f;
    isInit = true;
    invalidate();
  }

  private void init() {
    timer = new Timer();
    mDataList = new ArrayList<Pickers>();
    mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    mPaint.setStyle(Style.FILL);
    mPaint.setTextAlign(Align.CENTER);
    mPaint.setColor(mColorText);
  }

  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    // 根据index绘制view
    if (isInit)
      drawData(canvas);
  }

  private void drawData(Canvas canvas) {
    // 先绘制选中的text再往上往下绘制其余的text
    float scale = parabola(mViewHeight / 4.0f, mMoveLen);
    float size = (mMaxTextSize - mMinTextSize) * scale + mMinTextSize;
    mPaint.setTextSize(size);
    mPaint.setAlpha((int) ((mMaxTextAlpha - mMinTextAlpha) * scale + mMinTextAlpha));
    // text居中绘制，注意baseline的计算才能达到居中，y值是text中心坐标
    float x = (float) (mViewWidth / 2.0);
    float y = (float) (mViewHeight / 2.0 + mMoveLen);
    FontMetricsInt fmi = mPaint.getFontMetricsInt();
    float baseline = (float) (y - (fmi.bottom / 2.0 + fmi.top / 2.0));

    int indexs = mCurrentSelected;
    String textData = mDataList.get(indexs).getShowConetnt();
    canvas.drawText(textData, x, baseline, mPaint);

    // 绘制上方data
    for (int i = 1; (mCurrentSelected - i) >= 0; i++) {
      drawOtherText(canvas, i, -1);
    }
    // 绘制下方data
    for (int i = 1; (mCurrentSelected + i) < mDataList.size(); i++) {
      drawOtherText(canvas, i, 1);
    }
  }

  /**
   * @param canvas
   * @param position
   *      距离mCurrentSelected的差值
   * @param type
   *      1表示向下绘制，-1表示向上绘制
   */
  private void drawOtherText(Canvas canvas, int position, int type) {
    float d = (float) (MARGIN_ALPHA * mMinTextSize * position + type
        * mMoveLen);
    float scale = parabola(mViewHeight / 4.0f, d);
    float size = (mMaxTextSize - mMinTextSize) * scale + mMinTextSize;
    mPaint.setTextSize(size);
    mPaint.setAlpha((int) ((mMaxTextAlpha - mMinTextAlpha) * scale + mMinTextAlpha));
    float y = (float) (mViewHeight / 2.0 + type * d);
    FontMetricsInt fmi = mPaint.getFontMetricsInt();
    float baseline = (float) (y - (fmi.bottom / 2.0 + fmi.top / 2.0));

    int indexs = mCurrentSelected + type * position;
    String textData = mDataList.get(indexs).getShowConetnt();
    canvas.drawText(textData, (float) (mViewWidth / 2.0), baseline, mPaint);
  }

  /**
   * 抛物线
   * 
   * @param zero
   *      零点坐标
   * @param x
   *      偏移量
   * @return scale
   */
  private float parabola(float zero, float x) {
    float f = (float) (1 - Math.pow(x / zero, 2));
    return f < 0 ? 0 : f;
  }

  @Override
  public boolean onTouchEvent(MotionEvent event) {
    switch (event.getActionMasked()) {
    case MotionEvent.ACTION_DOWN:
      doDown(event);
      break;
    case MotionEvent.ACTION_MOVE:
      doMove(event);
      break;
    case MotionEvent.ACTION_UP:
      doUp(event);
      break;
    }
    return true;
  }

  private void doDown(MotionEvent event) {
    if (mTask != null) {
      mTask.cancel();
      mTask = null;
    }
    mLastDownY = event.getY();
  }

  private void doMove(MotionEvent event) {

    mMoveLen += (event.getY() - mLastDownY);

    if (mMoveLen > MARGIN_ALPHA * mMinTextSize / 2) {
      // 往下滑超过离开距离
      moveTailToHead();
      mMoveLen = mMoveLen - MARGIN_ALPHA * mMinTextSize;
    } else if (mMoveLen < -MARGIN_ALPHA * mMinTextSize / 2) {
      // 往上滑超过离开距离
      moveHeadToTail();
      mMoveLen = mMoveLen + MARGIN_ALPHA * mMinTextSize;
    }

    mLastDownY = event.getY();
    invalidate();
  }

  private void doUp(MotionEvent event) {
    // 抬起手后mCurrentSelected的位置由当前位置move到中间选中位置
    if (Math.abs(mMoveLen) < 0.0001) {
      mMoveLen = 0;
      return;
    }
    if (mTask != null) {
      mTask.cancel();
      mTask = null;
    }
    mTask = new MyTimerTask(updateHandler);
    timer.schedule(mTask, 0, 10);
  }

  class MyTimerTask extends TimerTask {
    Handler handler;

    public MyTimerTask(Handler handler) {
      this.handler = handler;
    }

    @Override
    public void run() {
      handler.sendMessage(handler.obtainMessage());
    }

  }

  public interface onSelectListener {
    void onSelect(Pickers pickers);
  }
}