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。