android:TimePicker仿照IOS時間選擇器,可自定義選擇器

背景:
項目要求寫一個選擇器:不僅僅是單純的時間,還包括自定義部分.
搜了很久,搜出來只用一個自定義view.java類,再簡單封裝下的選擇器:
貼下源碼:

public class PickerView extends View{
public static final String TAG = "PickerView";
/**
 * text之間間距和minTextSize之比
 */
public static final float MARGIN_ALPHA = 2.8f;
/**
 * 自動回滾到中間的速度
 */
public static final float SPEED = 2;

private List<String> mDataList;
/**
 * 選中的位置，這個位置是mDataList的中心位置，一直不變
 */
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;
/**
 * 滑動的距離
 */
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
            // 這裏mMoveLen / Math.abs(mMoveLen)是爲了保有mMoveLen的正負號，以實現上滾或下滾
            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();
}

/**
 * 選擇選中的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();
}

/**
 * 選擇選中的內容
 * 
 * @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()
{
    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的高度計算字體大小
    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);
    // 根據index繪製view
    if (isInit)
        drawData(canvas);
}

private void drawData(Canvas canvas)
{
    // 先繪製選中的text再往上往下繪製其餘的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居中繪製，注意baseline的計算才能達到居中，y值是text中心座標
    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);
    // 繪製上方data
    for (int i = 1; (mCurrentSelected - i) >= 0; i++)
    {
        drawOtherText(canvas, i, -1);
    }
    // 繪製下方data
    for (int i = 1; (mCurrentSelected + i) < mDataList.size(); i++)
    {
        drawOtherText(canvas, i, 1);
    }

}

/**
 * @param canvas
 * @param position
 *            距離mCurrentSelected的差值
 * @param type
 *            1表示向下繪製，-1表示向上繪製
 */
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);
}

/**
 * 拋物線
 * 
 * @param zero
 *            零點座標
 * @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)
    {
        // 往下滑超過離開距離
        moveTailToHead();
        mMoveLen = mMoveLen - MARGIN_ALPHA * mMinTextSize;
    } else if (mMoveLen < -MARGIN_ALPHA * mMinTextSize / 2)
    {
        // 往上滑超過離開距離
        moveHeadToTail();
        mMoveLen = mMoveLen + MARGIN_ALPHA * mMinTextSize;
    }

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

private void doUp(MotionEvent event)
{
    // 擡起手後mCurrentSelected的位置由當前位置move到中間選中位置
    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);
}

}
`

這裏定義的就是可以滾動的view,直接放入xml文件中即可