自定义轻量级的安卓滚轮选择控件

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.text.TextPaint;
import android.util.AttributeSet;
import android.util.TypedValue;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.widget.Scroller;

import java.util.ArrayList;

/**
 * 滚轮视图，可设置是否循环模式，实现OnScrollChangedListener接口以监听滚轮变化
 * Created by huzn on 2016/10/27.
 */
public class EasyPickerView extends View {

    // 文字大小
    private int textSize;
    // 颜色，默认Color.BLACK
    private int textColor;
    // 文字之间的间隔，默认10dp
    private int textPadding;
    // 文字最大放大比例，默认2.0f
    private float textMaxScale;
    // 文字最小alpha值，范围0.0f~1.0f，默认0.4f
    private float textMinAlpha;
    // 是否循环模式，默认是
    private boolean isRecycleMode;
    // 正常状态下最多显示几个文字，默认3（偶数时，边缘的文字会截断）
    private int maxShowNum;

    private TextPaint textPaint;
    private Paint.FontMetrics fm;

    private Scroller scroller;
    private VelocityTracker velocityTracker;
    private int minimumVelocity;
    private int maximumVelocity;
    private int scaledTouchSlop;

    // 数据
    private ArrayList<String> dataList = new ArrayList<>();
    // 中间x坐标
    private int cx;
    // 中间y坐标
    private int cy;
    // 文字最大宽度
    private float maxTextWidth;
    // 文字高度
    private int textHeight;
    // 实际内容宽度
    private int contentWidth;
    // 实际内容高度
    private int contentHeight;

    // 按下时的y坐标
    private float downY;
    // 本次滑动的y坐标偏移值
    private float offsetY;
    // 在fling之前的offsetY
    private float oldOffsetY;
    // 当前选中项
    private int curIndex;
    private int offsetIndex;

    // 回弹距离
    private float bounceDistance;
    // 是否正处于滑动状态
    private boolean isSliding = false;

    public EasyPickerView(Context context) {
        this(context, null);
    }

    public EasyPickerView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public EasyPickerView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);

        TypedArray a = context.getTheme().obtainStyledAttributes(attrs, R.styleable.EasyPickerView, defStyleAttr, 0);
        textSize = a.getDimensionPixelSize(R.styleable.EasyPickerView_epvTextSize, (int) TypedValue.applyDimension(
                TypedValue.COMPLEX_UNIT_SP, 16, getResources().getDisplayMetrics()));
        textColor = a.getColor(R.styleable.EasyPickerView_epvTextColor, Color.BLACK);
        textPadding = a.getDimensionPixelSize(R.styleable.EasyPickerView_epvTextPadding, (int) TypedValue.applyDimension(
                TypedValue.COMPLEX_UNIT_DIP, 20, getResources().getDisplayMetrics()));
        textMaxScale = a.getFloat(R.styleable.EasyPickerView_epvTextMaxScale, 2.0f);
        textMinAlpha = a.getFloat(R.styleable.EasyPickerView_epvTextMinAlpha, 0.4f);
        isRecycleMode = a.getBoolean(R.styleable.EasyPickerView_epvRecycleMode, true);
        maxShowNum = a.getInteger(R.styleable.EasyPickerView_epvMaxShowNum, 3);
        a.recycle();

        textPaint = new TextPaint();
        textPaint.setColor(textColor);
        textPaint.setTextSize(textSize);
        textPaint.setAntiAlias(true);
        fm = textPaint.getFontMetrics();

        scroller = new Scroller(context);
        minimumVelocity = ViewConfiguration.get(getContext()).getScaledMinimumFlingVelocity();
        maximumVelocity = ViewConfiguration.get(getContext()).getScaledMaximumFlingVelocity();
        scaledTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int mode = MeasureSpec.getMode(widthMeasureSpec);
        int width = MeasureSpec.getSize(widthMeasureSpec);
        contentWidth = (int) (maxTextWidth + getPaddingLeft() + getPaddingRight());
        if (mode != MeasureSpec.EXACTLY) { // wrap_content
            width = contentWidth;
        }

        mode = MeasureSpec.getMode(heightMeasureSpec);
        int height = MeasureSpec.getSize(heightMeasureSpec);
        textHeight = (int) (fm.bottom - fm.top);
        contentHeight = textHeight * maxShowNum + textPadding * maxShowNum;
        if (mode != MeasureSpec.EXACTLY) { // wrap_content
            height = contentHeight + getPaddingTop() + getPaddingBottom();
        }

        cx = width / 2;
        cy = height / 2;

        setMeasuredDimension(width, height);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        addVelocityTracker(event);
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                if (!scroller.isFinished()) {
                    scroller.forceFinished(true);
                    finishScroll();
                }
                downY = event.getY();
                break;

            case MotionEvent.ACTION_MOVE:
                offsetY = event.getY() - downY;
                if (isSliding || Math.abs(offsetY) > scaledTouchSlop) {
                    isSliding = true;
                    reDraw();
                }
                break;

            case MotionEvent.ACTION_UP:
                int scrollYVelocity = 2 * getScrollYVelocity() / 3;
                if (Math.abs(scrollYVelocity) > minimumVelocity) {
                    oldOffsetY = offsetY;
                    scroller.fling(0, 0, 0, scrollYVelocity, 0, 0, -Integer.MAX_VALUE, Integer.MAX_VALUE);
                    invalidate();
                } else {
                    finishScroll();
                }

                // 没有滑动，则判断点击事件
                if (!isSliding) {
                    if (downY < contentHeight / 3)
                        moveBy(-1);
                    else if (downY > 2 * contentHeight / 3)
                        moveBy(1);
                }

                isSliding = false;
                recycleVelocityTracker();
                break;
        }
        return true;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        if (null != dataList && dataList.size() > 0) {
            canvas.clipRect(
                    cx - contentWidth / 2,
                    cy - contentHeight / 2,
                    cx + contentWidth / 2,
                    cy + contentHeight / 2
            );

            // 绘制文字，从当前中间项往前2个开始，往后一共绘制5个字
            int size = dataList.size();
            int centerPadding = textHeight + textPadding;
            int half = maxShowNum / 2 + 1;
            for (int i = -half; i <= half; i++) {
                int index = curIndex - offsetIndex + i;

                if (isRecycleMode) {
                    if (index < 0)
                        index = (index + 1) % dataList.size() + dataList.size() - 1;
                    else if (index > dataList.size() - 1)
                        index = index % dataList.size();
                }

                if (index >= 0 && index < size) {
                    // 计算每个字的中间y坐标
                    int tempY = cy + i * centerPadding;
                    tempY += offsetY % centerPadding;

                    // 根据每个字中间y坐标到cy的距离，计算出scale值
                    float scale = 1.0f - (1.0f * Math.abs(tempY - cy) / centerPadding);

                    // 根据textMaxScale，计算出tempScale值，即实际text应该放大的倍数，范围 1~textMaxScale
                    float tempScale = scale * (textMaxScale - 1.0f) + 1.0f;
                    tempScale = tempScale < 1.0f ? 1.0f : tempScale;
                    textPaint.setTextSize(textSize * tempScale);
                    textPaint.setAlpha((int) (255 * textMinAlpha * tempScale));

                    // 绘制
                    Paint.FontMetrics tempFm = textPaint.getFontMetrics();
                    String text = dataList.get(index);
                    float textWidth = textPaint.measureText(text);
                    canvas.drawText(text, cx - textWidth / 2, tempY - (tempFm.ascent + tempFm.descent) / 2, textPaint);
                }
            }
        }
    }

    @Override
    public void computeScroll() {
        if (scroller.computeScrollOffset()) {
            offsetY = oldOffsetY + scroller.getCurrY();

            if (!scroller.isFinished())
                reDraw();
            else
                finishScroll();
        }
    }

    private void addVelocityTracker(MotionEvent event) {
        if (velocityTracker == null)
            velocityTracker = VelocityTracker.obtain();

        velocityTracker.addMovement(event);
    }

    private void recycleVelocityTracker() {
        if (velocityTracker != null) {
            velocityTracker.recycle();
            velocityTracker = null;
        }
    }

    private int getScrollYVelocity() {
        velocityTracker.computeCurrentVelocity(1000, maximumVelocity);
        int velocity = (int) velocityTracker.getYVelocity();
        return velocity;
    }

    private void reDraw() {
        // curIndex需要偏移的量
        int i = (int) (offsetY / (textHeight + textPadding));
        if (isRecycleMode || (curIndex - i >= 0 && curIndex - i < dataList.size())) {
            if (offsetIndex != i) {
                offsetIndex = i;

                if (null != onScrollChangedListener)
                    onScrollChangedListener.onScrollChanged(getNowIndex(-offsetIndex));
            }
            postInvalidate();
        } else {
            finishScroll();
        }
    }

    private void finishScroll() {
        // 判断结束滑动后应该停留在哪个位置
        int centerPadding = textHeight + textPadding;
        float v = offsetY % centerPadding;
        if (v > 0.5f * centerPadding)
            ++offsetIndex;
        else if (v < -0.5f * centerPadding)
            --offsetIndex;

        // 重置curIndex
        curIndex = getNowIndex(-offsetIndex);

        // 计算回弹的距离
        bounceDistance = offsetIndex * centerPadding - offsetY;
        offsetY += bounceDistance;

        // 更新
        if (null != onScrollChangedListener)
            onScrollChangedListener.onScrollFinished(curIndex);

        // 重绘
        reset();
        postInvalidate();
    }

    private int getNowIndex(int offsetIndex) {
        int index = curIndex + offsetIndex;
        if (isRecycleMode) {
            if (index < 0)
                index = (index + 1) % dataList.size() + dataList.size() - 1;
            else if (index > dataList.size() - 1)
                index = index % dataList.size();
        } else {
            if (index < 0)
                index = 0;
            else if (index > dataList.size() - 1)
                index = dataList.size() - 1;
        }
        return index;
    }

    private void reset() {
        offsetY = 0;
        oldOffsetY = 0;
        offsetIndex = 0;
        bounceDistance = 0;
    }

    /**
     * 设置要显示的数据
     *
     * @param dataList 要显示的数据
     */
    public void setDataList(ArrayList<String> dataList) {
        this.dataList.clear();
        this.dataList.addAll(dataList);

        // 更新maxTextWidth
        if (null != dataList && dataList.size() > 0) {
            int size = dataList.size();
            for (int i = 0; i < size; i++) {
                float tempWidth = textPaint.measureText(dataList.get(i));
                if (tempWidth > maxTextWidth)
                    maxTextWidth = tempWidth;
            }
            curIndex = 0;
        }
        requestLayout();
    }

    /**
     * 获取当前状态下，选中的下标
     *
     * @return 选中的下标
     */
    public int getCurIndex() {
        return curIndex - offsetIndex;
    }

    /**
     * 滚动到指定位置
     *
     * @param index 需要滚动到的指定位置
     */
    public void moveTo(int index) {
        if (index < 0 || index >= dataList.size() || curIndex == index)
            return;

        if (!scroller.isFinished())
            scroller.forceFinished(true);

        finishScroll();

        int dy = 0;
        int centerPadding = textHeight + textPadding;
        if (!isRecycleMode) {
            dy = (curIndex - index) * centerPadding;
        } else {
            int offsetIndex = curIndex - index;
            int d1 = Math.abs(offsetIndex) * centerPadding;
            int d2 = (dataList.size() - Math.abs(offsetIndex)) * centerPadding;

            if (offsetIndex > 0) {
                if (d1 < d2)
                    dy = d1; // ascent
                else
                    dy = -d2; // descent
            } else {
                if (d1 < d2)
                    dy = -d1; // descent
                else
                    dy = d2; // ascent
            }
        }
        scroller.startScroll(0, 0, 0, dy, 500);
        invalidate();
    }

    /**
     * 滚动指定的偏移量
     *
     * @param offsetIndex 指定的偏移量
     */
    public void moveBy(int offsetIndex) {
        moveTo(getNowIndex(offsetIndex));
    }

    /**
     * 滚动发生变化时的回调接口
     */
    public interface OnScrollChangedListener {
        public void onScrollChanged(int curIndex);

        public void onScrollFinished(int curIndex);
    }

    private OnScrollChangedListener onScrollChangedListener;

    public void setOnScrollChangedListener(OnScrollChangedListener onScrollChangedListener) {
        this.onScrollChangedListener = onScrollChangedListener;
    }
}

 MainActivity.java

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {

    private int hour;
    private int minute;
    private TextView tv;
    private EasyPickerView epvH;
    private EasyPickerView epvM;

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

        tv = (TextView) findViewById(R.id.tv);

        // hours
        initHours();

        // minutes
        initMinutes();

        // btns
        initBtns();
    }

    private void initHours() {
        epvH = (EasyPickerView) findViewById(R.id.epv_h);
        final ArrayList<String> hDataList = new ArrayList<>();
        for (int i = 0; i < 24; i++)
            hDataList.add("" + i);

        epvH.setDataList(hDataList);
        epvH.setOnScrollChangedListener(new EasyPickerView.OnScrollChangedListener() {
            @Override
            public void onScrollChanged(int curIndex) {
                hour = Integer.parseInt(hDataList.get(curIndex));
                tv.setText(hour + "h" + minute + "m");
            }

            @Override
            public void onScrollFinished(int curIndex) {
                hour = Integer.parseInt(hDataList.get(curIndex));
                tv.setText(hour + "h" + minute + "m");
            }
        });
    }

    private void initMinutes() {
        epvM = (EasyPickerView) findViewById(R.id.epv_m);
        final ArrayList<String> dataList2 = new ArrayList<>();
        for (int i = 0; i < 60; i++)
            dataList2.add("" + i);

        epvM.setDataList(dataList2);
        epvM.setOnScrollChangedListener(new EasyPickerView.OnScrollChangedListener() {
            @Override
            public void onScrollChanged(int curIndex) {
                minute = Integer.parseInt(dataList2.get(curIndex));
                tv.setText(hour + "h" + minute + "m");
            }

            @Override
            public void onScrollFinished(int curIndex) {
                minute = Integer.parseInt(dataList2.get(curIndex));
                tv.setText(hour + "h" + minute + "m");
            }
        });
    }

    private void initBtns() {
        // hours
        final EditText et_h = (EditText) findViewById(R.id.et_h);

        Button btnTo = (Button) findViewById(R.id.btn_to_h);
        btnTo.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (!TextUtils.isEmpty(et_h.getText())) {
                    int index = Integer.parseInt(et_h.getText().toString());
                    epvH.moveTo(index);
                }
            }
        });

        Button btnBy = (Button) findViewById(R.id.btn_by_h);
        btnBy.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (!TextUtils.isEmpty(et_h.getText())) {
                    int index = Integer.parseInt(et_h.getText().toString());
                    epvH.moveBy(index);
                }
            }
        });

        // minutes
        final EditText et_m = (EditText) findViewById(R.id.et_m);

        Button btnTo_m = (Button) findViewById(R.id.btn_to_m);
        btnTo_m.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (!TextUtils.isEmpty(et_m.getText())) {
                    int index = Integer.parseInt(et_m.getText().toString());
                    epvM.moveTo(index);
                }
            }
        });

        Button btnBy_m = (Button) findViewById(R.id.btn_by_m);
        btnBy_m.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (!TextUtils.isEmpty(et_m.getText())) {
                    int index = Integer.parseInt(et_m.getText().toString());
                    epvM.moveBy(index);
                }
            }
        });
    }
}

 activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:custom="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.hzn.easypickerview.MainActivity"
    >

    <TextView
        android:id="@+id/tv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="30dp"
        android:textColor="#8f8f8f"
        android:textSize="20sp"
        />

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        >

        <com.hzn.easypickerview.EasyPickerView
            android:id="@+id/epv_h"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:paddingLeft="15dp"
            android:paddingRight="15dp"
            custom:epvMaxShowNum="3"
            custom:epvRecycleMode="true"
            custom:epvTextColor="#4aa4a4"
            custom:epvTextMaxScale="2.0"
            custom:epvTextMinAlpha="0.35"
            custom:epvTextPadding="10dp"
            custom:epvTextSize="30sp"
            />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="5dp"
            android:layout_marginTop="70dp"
            android:text="h"
            android:textColor="#4aa4a4"
            android:textSize="20sp"
            />

        <com.hzn.easypickerview.EasyPickerView
            android:id="@+id/epv_m"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="10dp"
            android:paddingLeft="15dp"
            android:paddingRight="15dp"
            custom:epvMaxShowNum="3"
            custom:epvRecycleMode="false"
            custom:epvTextColor="#e98d3c"
            custom:epvTextMaxScale="2.0"
            custom:epvTextMinAlpha="0.35"
            custom:epvTextPadding="10dp"
            custom:epvTextSize="30sp"
            />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="5dp"
            android:layout_marginTop="70dp"
            android:text="m"
            android:textColor="#e98d3c"
            android:textSize="20sp"
            />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="40dp"
        android:gravity="center"
        android:orientation="horizontal"
        >

        <EditText
            android:id="@+id/et_h"
            android:layout_width="60dp"
            android:layout_height="40dp"
            android:hint="h"
            android:inputType="numberSigned"
            android:textColor="#4aa4a4"
            android:textColorHint="#dedede"
            />

        <Button
            android:id="@+id/btn_to_h"
            android:layout_width="wrap_content"
            android:layout_height="30dp"
            android:layout_marginLeft="10dp"
            android:background="#4aa4a4"
            android:text="move to"
            android:textColor="#ffffff"
            />

        <Button
            android:id="@+id/btn_by_h"
            android:layout_width="wrap_content"
            android:layout_height="30dp"
            android:layout_marginLeft="10dp"
            android:background="#4aa4a4"
            android:minHeight="0dp"
            android:text="move by"
            android:textColor="#ffffff"
            />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="20dp"
        android:gravity="center"
        android:orientation="horizontal"
        >

        <EditText
            android:id="@+id/et_m"
            android:layout_width="60dp"
            android:layout_height="40dp"
            android:hint="m"
            android:inputType="numberSigned"
            android:textColor="#4aa4a4"
            android:textColorHint="#dedede"
            />

        <Button
            android:id="@+id/btn_to_m"
            android:layout_width="wrap_content"
            android:layout_height="30dp"
            android:layout_marginLeft="10dp"
            android:background="#e98d3c"
            android:text="move to"
            android:textColor="#ffffff"
            />

        <Button
            android:id="@+id/btn_by_m"
            android:layout_width="wrap_content"
            android:layout_height="30dp"
            android:layout_marginLeft="10dp"
            android:background="#e98d3c"
            android:text="move by"
            android:textColor="#ffffff"
            />
    </LinearLayout>
</LinearLayout>

 rec.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
       android:shape="rectangle"
    >

    <corners android:radius="8dp"/>
    <solid android:color="#f1f1f1"/>
    <stroke
        android:width="1dp"
        android:color="#af1e7f"
        />
</shape>

 atts.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="EasyPickerView">
        <attr name="epvTextSize" format="dimension"/>
        <attr name="epvTextColor" format="color"/>
        <attr name="epvTextPadding" format="dimension"/>
        <attr name="epvTextMaxScale" format="float"/>
        <attr name="epvTextMinAlpha" format="float"/>
        <attr name="epvRecycleMode" format="boolean"/>
        <attr name="epvMaxShowNum" format="integer"/>
    </declare-styleable>
</resources>

 效果图：

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学习来源：http://blog.csdn.net/u012199331/article/details/72778973

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