Android PickerView滚动选择器的使用方法

2020-01-02 07:00:20

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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。

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