Android PickerView的实现

/*
* 使用：xml文件中直接引用，需要多少列数据就用多少个PickerView
* 在Activity中：获取到PickerView实例后，使用setData()方法设置数据，其他方法见103行
* 关联数据:比如现在第一列选中xx市,可以在监听中为第二个PickerView调用setData()来更新第二列的数据
*/
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;
/**
* 默认初始化时选中的位置，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();
}

};

//构造方法都调用init
public PickerView(Context context)
{
super(context);
init();
}

public PickerView(Context context, AttributeSet attrs)
{
super(context, attrs);
init();
}
//以下为主要使用的public方法---------------------------------------------------------------------------------

/*
* 获取到当前选中的数据在数据集中的position
*/
public int getCurrentItem(){
return mCurrentSelected;
};
/*
* 设置监听,这个onSelectedLisener需要实现一个onSelect(String text)方法
* text是当前显示的数据
*/
public void setOnSelectListener(onSelectListener listener)
{
mSelectListener = listener;
}
/*
* 设置数据集，参数类型为List
*/
public void setData(List<String> datas)
{
mDataList = datas;
mCurrentSelected = datas.size() / 2;
invalidate();
}
/*
* 设置当前选中的数据
*/
public void setSelected(int selected)
{
mCurrentSelected = selected;
}

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

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(Paint.Style.FILL);
mPaint.setTextAlign(Paint.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);
Paint.FontMetricsInt fmi = mPaint.getFontMetricsInt();
float baseline = (float) (y - (fmi.bottom / 2.0 + fmi.top / 2.0));

canvas.drawText(mDataList.get(mCurrentSelected), x, baseline, mPaint);
Paint linePaint=new Paint();
linePaint.setColor(Color.LTGRAY);
linePaint.setStrokeWidth(3);

// 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);
Paint.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);
}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">
<LinearLayout
android:layout_centerHorizontal="true"
android:orientation="horizontal"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
<com.liu.pickerview.PickerView
android:id="@+id/year_picker"
android:layout_width="100dp"
android:layout_height="100dp" />
<com.liu.pickerview.PickerView
android:id="@+id/month_picker"
android:layout_width="100dp"
android:layout_height="100dp" />
</LinearLayout>

</RelativeLayout>

public class MainActivity extends AppCompatActivity {
private PickerView year, month;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

year = (PickerView) findViewById(R.id.year_picker);
month = (PickerView) findViewById(R.id.month_picker);

ArrayList<String> month_list=new ArrayList<>();
for (int i=0;i<12;i++){
month_list.add(i + "");
}
ArrayList<String> year_list=new ArrayList<>();
for (int i=0;i<100;i++){
year_list.add( i + "");
}

year.setData(year_list);
month.setData(month_list);

year.setOnSelectListener(new PickerView.onSelectListener() {
@Override
public void onSelect(String text) {
Log.i("tag","选择了"+text);
}
});
month.setOnSelectListener(new PickerView.onSelectListener() {
@Override
public void onSelect(String text) {
Log.i("tag","选择了"+text);
}
});
}
}