Android PickerView滚动选择器的使用方法

手机里设置闹钟需要选择时间，那个选择时间的控件就是滚动选择器，前几天用手机刷了MIUI，发现自带的那个时间选择器效果挺好看的，于是就自己仿写了一个，权当练手。先来看效果：

效果还行吧？实现思路就是自定义一个PickerView，单独滚动的是一个PickerView，显然上图中有分和秒的选择所以在布局里用了两个PickerView。由于这里不涉及到text的点击事件，所以只需要继承View就行了，直接把text用canvas画上去。PickerView的实现的主要难点：

难点1：

字体随距离的渐变。可以看到，text随离中心位置的距离变化而变化，这里变化的是透明度alpha和字体大小TexSize，这两个值我都设置了Max和Min值，通过其与中心点的距离计算scale。我用的是变化曲线是抛物线scale=1-ax^2(x<=Height/4),scale = 0(x>Height/4)，a=(4/Height)^2。x就是距离View中心的偏移量。用图片表示如下：

难点2：

text的居中。绘制text的时候不仅要使其在x方向上居中，还要在y方向上居中，在x方向上比较简单，设置Paint的Align为Align.CENTER就行了，但是y方向上很蛋疼，需要计算text的baseline。

难点3：

循环滚动。为了解决循环滚动的问题我把存放text的List从中间往上下摊开，通过不断地moveHeadToTail和moveTailToHead使选中的text始终是list的中间position的值。

以上就是几个难点，了解了之后可以来看PickerView的代码了：

package com.jingchen.timerpicker; 

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

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; 

/**
 * 滚动选择器
 *
 * @author chenjing
 *
 */
public class PickerView 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<String> 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 = 80;
  private float mMinTextSize = 40; 

  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 PickerView(Context context)
  {
    super(context);
    init();
  } 

  public PickerView(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<String> datas)
  {
    mDataList = datas;
    mCurrentSelected = datas.size() / 2;
    invalidate();
  } 

  public void setSelected(int selected)
  {
    mCurrentSelected = selected;
  } 

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

  private void moveTailToHead()
  {
    String 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 / 4.0f;
    mMinTextSize = mMaxTextSize / 2f;
    isInit = true;
    invalidate();
  } 

  private void init()
  {
    timer = new Timer();
    mDataList = new ArrayList<String>();
    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)); 

    canvas.drawText(mDataList.get(mCurrentSelected), 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));
    canvas.drawText(mDataList.get(mCurrentSelected + type * position),
        (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(String text);
  }
}

代码里的注释都写的很清楚了。接下来，我们就用写好的PickerView实现文章开头的图片效果吧~
首先看MainActivity的布局：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:background="#000000" > 

  <RelativeLayout
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerInParent="true"
    android:background="#ffffff" > 

    <com.jingchen.timerpicker.PickerView
      android:id="@+id/minute_pv"
      android:layout_width="80dp"
      android:layout_height="160dp" /> 

    <TextView
      android:id="@+id/minute_tv"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_centerVertical="true"
      android:layout_toRightOf="@id/minute_pv"
      android:text="分"
      android:textColor="#ffaa33"
      android:textSize="26sp"
      android:textStyle="bold" /> 

    <com.jingchen.timerpicker.PickerView
      android:id="@+id/second_pv"
      android:layout_width="80dp"
      android:layout_height="160dp"
      android:layout_toRightOf="@id/minute_tv" /> 

    <TextView
      android:id="@+id/second_tv"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_centerVertical="true"
      android:layout_toRightOf="@id/second_pv"
      android:text="秒"
      android:textColor="#ffaa33"
      android:textSize="26sp"
      android:textStyle="bold" />
  </RelativeLayout> 

</RelativeLayout>

两个PickerView两个TextView，很简单。
下面是MainActivity的代码：

package com.jingchen.timerpicker; 

import java.util.ArrayList;
import java.util.List; 

import com.jingchen.timerpicker.PickerView.onSelectListener; 

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.widget.TextView;
import android.widget.Toast; 

public class MainActivity extends Activity
{ 

  PickerView minute_pv;
  PickerView second_pv; 

  @Override
  protected void onCreate(Bundle savedInstanceState)
  {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    minute_pv = (PickerView) findViewById(R.id.minute_pv);
    second_pv = (PickerView) findViewById(R.id.second_pv);
    List<String> data = new ArrayList<String>();
    List<String> seconds = new ArrayList<String>();
    for (int i = 0; i < 10; i++)
    {
      data.add("0" + i);
    }
    for (int i = 0; i < 60; i++)
    {
      seconds.add(i < 10 ? "0" + i : "" + i);
    }
    minute_pv.setData(data);
    minute_pv.setOnSelectListener(new onSelectListener()
    { 

      @Override
      public void onSelect(String text)
      {
        Toast.makeText(MainActivity.this, "选择了 " + text + " 分",
            Toast.LENGTH_SHORT).show();
      }
    });
    second_pv.setData(seconds);
    second_pv.setOnSelectListener(new onSelectListener()
    { 

      @Override
      public void onSelect(String text)
      {
        Toast.makeText(MainActivity.this, "选择了 " + text + " 秒",
            Toast.LENGTH_SHORT).show();
      }
    });
  } 

  @Override
  public boolean onCreateOptionsMenu(Menu menu)
  {
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
  } 

}

OK了，自定义自己的TimerPicker就是这么简单

源码下载：PickerView滚动选择器

希望本文对大家学习滚动选择器PickerView有所帮助。