00CA6045E4F124CC21BF813006E740A8.gif
代码：
package com.example.gyfpickerview;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.support.annotation.Nullable;
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;
/**
* Created by 龚勇峰 on 2017/6/22.
*/
public class GyfPickerView extends View {
//文字大小
private int textSize;
//文字顔色，默认color.blcak
private int textColor;
//文字之间的间隔；默认10dp
private int textPading;
//文字放大比例，默认2.0f
private float textMaxScale;
//文本最小的alpha
private float textMinAlpha;
//时候循环，默认循环
private boolean isRecycleMode;
//文本对象，主要有 top bottom asent，desent，四个属性
private Paint.FontMetrics fm;
//显示的行数，默认是3
private int maxShowNum;
private Scroller scroller;
//速率追踪器
private VelocityTracker velocityTracker;
//数据
private ArrayList dataList = new ArrayList<>();
//中间x坐标
private int cx;
//中间y坐标
private int cy;
//文字的最大宽度
private float textMaxwidth;
//文字的高度
private int textHeight;
//实际内容的宽度
private int contentWidth;
//实际内容的高度
private int contentHeight;
//按下时y的坐标
private float downY;
//本次滑动Y坐标的偏移值
private float offsetY;
//在fling之前的offsetY
private float oldOffsetY;
//当前的选中项
private int curIndex;
//滚动的偏移项
private int offsetIndex;
//回弹距离
private float bonceDistance;
//是否处于滑动状态
private boolean isSilding = false;
private TextPaint textPaint;
private int minNumVelocity;
private int maxNumVelocity;
private int scaleTouchSlop;
public GyfPickerView(Context context) {
this(context, null);
}
public GyfPickerView(Context context, @Nullable AttributeSet attrs) {
this(context, attrs, 0);
}
public GyfPickerView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.GyfPickerView);
textSize = a.getDimensionPixelSize(R.styleable.GyfPickerView_gyfTextSize,
getDimension(TypedValue.COMPLEX_UNIT_SP, 16, context));
textColor = a.getColor(R.styleable.GyfPickerView_gyfTextColor, Color.BLACK);
textPading = a.getDimensionPixelSize(R.styleable.GyfPickerView_gyfTextPading, getDimension(
TypedValue.COMPLEX_UNIT_DIP, 20, context));
textMaxScale = a.getFloat(R.styleable.GyfPickerView_gfyTextMaxScale, 2.0f);
textMinAlpha = a.getFloat(R.styleable.GyfPickerView_gyfTextMinAlpha, 0.4f);
isRecycleMode = a.getBoolean(R.styleable.GyfPickerView_gyfRecycleMode, true);
maxShowNum = a.getInteger(R.styleable.GyfPickerView_gyfMaxShowNum, 3);
a.recycle();
textPaint = new TextPaint(Paint.ANTI_ALIAS_FLAG);
textPaint.setColor(textColor);
textPaint.setTextSize(textSize);
fm = textPaint.getFontMetrics();
scroller = new Scroller(context);
velocityTracker = VelocityTracker.obtain();
minNumVelocity = ViewConfiguration.get(context).getScaledMinimumFlingVelocity();
maxNumVelocity = ViewConfiguration.get(context).getScaledMaximumFlingVelocity();
scaleTouchSlop = ViewConfiguration.get(context).getScaledTouchSlop();
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
//测量宽度
int mode = MeasureSpec.getMode(widthMeasureSpec);
int width = MeasureSpec.getSize(widthMeasureSpec);
contentWidth = (int) (textMaxwidth * textMaxScale + getPaddingLeft() + getPaddingRight());
if (mode != MeasureSpec.EXACTLY) {
//处理warp_content的情况
width = contentWidth;
}
//测量高度
mode = MeasureSpec.getMode(heightMeasureSpec);
int height = MeasureSpec.getSize(heightMeasureSpec);
textHeight = (int) (fm.bottom - fm.top);
contentHeight = textHeight * maxShowNum + textPading * maxShowNum;
if (mode != MeasureSpec.EXACTLY) {
height = contentHeight + getPaddingTop() + getPaddingBottom();
}
setMeasuredDimension(width, height);
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
//确定中心点坐标
cx = w / 2;
cy = h / 2;
}
@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 (isSilding || Math.abs(offsetY) > scaleTouchSlop) {
isSilding = true;
reDraw();
}
break;
case MotionEvent.ACTION_UP:
int scrollYVelocity = 2 * getScrollYVelocity() / 3;
if (Math.abs(scrollYVelocity) > minNumVelocity) {
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 (!isSilding) {
if (downY < contentHeight / 3)
moveBy(-1);
else if (downY > 2 * contentHeight / 3)
moveBy(1);
}
isSilding = false;
recycleVelocityTacvker();
break;
}
return true;
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
if (dataList.isEmpty())
return;
//规定的绘制区域，我们要绘制maxShowCount+2个，但只显示maxShowCount
canvas.clipRect(cx - contentWidth / 2, cy - contentHeight / 2,
cx + contentWidth / 2, cy + contentHeight / 2);
//绘制文字
int size = dataList.size();
int contentPadding = textHeight + textPading;
int half = maxShowNum / 2 + 1;
for (int i = -half; i <= half; i++) {
//当前要绘制的字符对应的下标
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) {
//计算每个字的中间坐标
int tempY = cy + i * contentPadding;
tempY += offsetY % contentPadding;
//根据每个字中间y坐标到cy的距离，计算出scale的值
float scale = 1.0f - (1.0f * Math.abs(tempY - cy) / contentPadding);
//根据textMaxScale，计算出tempScale，范围为1-textMaxScale
float tempScale = scale * (textMaxScale - 1.0f) + 1.0f;
tempScale = tempScale < 1.0f ? 1.0f : tempScale;
//计算文字的alpha值
float textAlpha=textMinAlpha;
if (textMaxScale != 1) {
float tempAlpha = (tempScale - 1) / (textMaxScale - 1);
textAlpha = (1 - textMinAlpha) * tempAlpha + textMinAlpha;
}
textPaint.setTextSize(textSize * tempScale);
textPaint.setAlpha((int) (255 * textAlpha));
// 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);
}
}
}
//标准尺寸转化
private int getDimension(int unit, float value, Context context) {
return (int) TypedValue.applyDimension(unit, value, context.getResources().getDisplayMetrics());
}
/**
* 设置要显示的数据
*
* @param dataList 要显示的数据
*/
public void setDataList(ArrayList 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 > textMaxwidth)
textMaxwidth = tempWidth;
}
curIndex = 0;
}
requestLayout();
invalidate();
}
//添加速率追踪器
private void addVelocityTracker(MotionEvent event){
if (velocityTracker==null)
velocityTracker=VelocityTracker.obtain();
velocityTracker.addMovement(event);
}
//回收
private void recycleVelocityTacvker(){
if (velocityTracker!=null)
velocityTracker.recycle();
velocityTracker=null;
}
//得到速率值
private int getScrollYVelocity() {
velocityTracker.computeCurrentVelocity(1000, maxNumVelocity);
int velocity = (int) velocityTracker.getYVelocity();
return velocity;
}
//滚动时重新绘制
private void reDraw() {
// curIndex需要偏移的量
int i = (int) (offsetY / (textHeight + textPading));
if (isRecycleMode || (curIndex - i >= 0 && curIndex - i < dataList.size())) {
if (offsetIndex != i) {
offsetIndex = i;
if (null != onScrollChangedListener)
onScrollChangedListener.onScrollChanged(getNowIndex(-offsetIndex),this);
}
postInvalidate();
} else {
finishScroll();
}
}
//结束滚动
private void finishScroll() {
// 判断结束滑动后应该停留在哪个位置
int centerPadding = textHeight + textPading;
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
bonceDistance = offsetIndex * centerPadding - offsetY;
offsetY += bonceDistance;
// 更新
if (null != onScrollChangedListener)
onScrollChangedListener.onScrollFinished(curIndex,this);
// 重绘
reset();
postInvalidate();
}
//得到当前的选中项
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;
}
/**
* 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 + textPading;
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();
}
//回复数据
private void reset() {
offsetY = 0;
oldOffsetY = 0;
offsetIndex = 0;
bonceDistance = 0;
}
/**
* 滚动发生变化时的回调接口
*/
public interface OnScrollChangedListener {
public void onScrollChanged(int curIndex,View view);
public void onScrollFinished(int curIndex,View view);
}
@Override
public void computeScroll() {
if (scroller.computeScrollOffset()) {
offsetY = oldOffsetY + scroller.getCurrY();
if (!scroller.isFinished())
reDraw();
else
finishScroll();
}
}
private OnScrollChangedListener onScrollChangedListener;
public void setOnScrollChangedListener(OnScrollChangedListener onScrollChangedListener) {
this.onScrollChangedListener = onScrollChangedListener;
}
}
Github地址：https://github.com/momoshusheng/GyfPickerView