Android 仿 iphone 自定义滚动选择器

背景：其实我们都知道，在我们做开发的过程中，会遇到Android 自身所带控件不够的情况，那么这个时候，就需要我们自定义控件，所以，也就造成了，在开发的过程中，我们一定要掌握好自定义控件，不然，当你去一家公司，产品萌妹子过来找你，这个效果很不错，问你能不能实现的时候，你难道能有理由说不行么，男人嘛，哪里能说不行了，直接用浑厚的声音告诉她，行，怎么不行，直接KO她。

一：多的不说，效果图，先走起

哎，请见谅，不会做那种动画的效果图

二：实例源码

（1）自定义控件

package com.pickerscrollview.views;

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

import android.annotation.SuppressLint;
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;

import com.pickerscrollview.bean.Pickers;

/**
 * 自定义滚动选择器
 * 
 * @author zengtao 2015年5月20日 下午7:36:03
 *
 */
@SuppressLint({ "HandlerLeak", "ClickableViewAccessibility" })
public class PickerScrollView 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<Pickers> 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 = 20;
    private float mMinTextSize = 10;

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

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

    /**
     * 选择选中的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();
    }

    /**
     * 选择选中的内容
     * 
     * @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() {
        Pickers head = mDataList.get(0);
        mDataList.remove(0);
        mDataList.add(head);
    }

    private void moveTailToHead() {
        Pickers 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 / 8.0f;
        mMinTextSize = mMaxTextSize / 2f;
        isInit = true;
        invalidate();
    }

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

        int indexs = mCurrentSelected;
        String textData = mDataList.get(indexs).getShowConetnt();
        canvas.drawText(textData, 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));

        int indexs = mCurrentSelected + type * position;
        String textData = mDataList.get(indexs).getShowConetnt();
        canvas.drawText(textData, (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(Pickers pickers);
    }
}

（2）实体类

package com.pickerscrollview.bean;

import java.io.Serializable;

/**
 * 
 * @author zengtao 2015年5月20日下午7:18:14
 *
 */
public class Pickers implements Serializable {

    private static final long serialVersionUID = 1L;

    private String showConetnt;
    private String showId;

    public String getShowConetnt() {
        return showConetnt;
    }

    public String getShowId() {
        return showId;
    }

    public Pickers(String showConetnt, String showId) {
        super();
        this.showConetnt = showConetnt;
        this.showId = showId;
    }

    public Pickers() {
        super();
    }

}

package com.pickerscrollview.ui;

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

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.RelativeLayout;

import com.pickerscrollview.bean.Pickers;
import com.pickerscrollview.views.PickerScrollView;
import com.pickerscrollview.views.PickerScrollView.onSelectListener;

/**
 * 主界面
 * 
 * @author zengtao 2015年5月20日 下午7:36:03
 *
 */
public class MainActivity extends Activity {

    private Button bt_scrollchoose; // 滚动选择器按钮
    private PickerScrollView pickerscrlllview; // 滚动选择器
    private List<Pickers> list; // 滚动选择器数据
    private String[] id;
    private String[] name;

    private Button bt_yes; // 确定按钮
    private RelativeLayout picker_rel; // 选择器布局

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        initView();
        initLinstener();
        initData();
    }

    /**
     * 初始化
     */
    private void initView() {
        bt_scrollchoose = (Button) findViewById(R.id.bt_scrollchoose);
        picker_rel = (RelativeLayout) findViewById(R.id.picker_rel);
        pickerscrlllview = (PickerScrollView) findViewById(R.id.pickerscrlllview);
        bt_yes = (Button) findViewById(R.id.picker_yes);
    }

    /**
     * 设置监听事件
     */
    private void initLinstener() {
        bt_scrollchoose.setOnClickListener(onClickListener);
        pickerscrlllview.setOnSelectListener(pickerListener);
        bt_yes.setOnClickListener(onClickListener);
    }

    /**
     * 初始化数据
     */
    private void initData() {
        list = new ArrayList<Pickers>();
        id = new String[] { "1", "2", "3", "4", "5", "6" };
        name = new String[] { "中国银行", "农业银行", "招商银行", "工商银行", "建设银行", "民生银行" };
        for (int i = 0; i < name.length; i++) {
            list.add(new Pickers(name[i], id[i]));
        }
        // 设置数据，默认选择第一条
        pickerscrlllview.setData(list);
        pickerscrlllview.setSelected(0);
    }

    // 滚动选择器选中事件
    onSelectListener pickerListener = new onSelectListener() {

        @Override
        public void onSelect(Pickers pickers) {
            System.out.println("选择：" + pickers.getShowId() + "--银行："
                    + pickers.getShowConetnt());
        }
    };

    // 点击监听事件
    OnClickListener onClickListener = new OnClickListener() {

        @Override
        public void onClick(View v) {
            if (v == bt_scrollchoose) {
                picker_rel.setVisibility(View.VISIBLE);
            } else if (v == bt_yes) {
                picker_rel.setVisibility(View.GONE);
            }
        }
    };
}

先做一下解析，在滑动手指的时候，有一个突出的点，就是有点像圆弧那个弧度一样的感觉，所以我们要用parabola这个方法去计算出来，画多大的字也是需要计算控件的高度，和宽度来绘制，首先我们先绘制中间的文体，在绘制上下两边的字，当然，我们也要设置一个手势监听，用于监听用户按下，滑动，抬起的时候，的一个操作，我们会根据手指往上移动和向下移动距离的多少来判断显示那个文字，选中了那个。

Demo下载地址：http://download.csdn.net/detail/u011546655/8729407