Android自定义控件实战——滚动选择器PickerView续

最近做项目，遇到一个需要实现滚动选择的需求。以前做过一个自定义实现滚动选择的view(https://blog.csdn.net/u014763302/article/details/53104814)，但发现不大符合需求。本着快速实现的目标，就找到了这为大神的博客（https://blog.csdn.net/zhongkejingwang/article/details/38513301），看了下实现的差不多了，就拿过来用，顺便加了一些小功能，并对存在的bug做了一些优化，特记录。

目前需求：

• 上下可循环滚动选择
• 点击按钮自动上下滚动一格

效果如下：

思路讲解：

由于代码本身是基于上面博文的基础上来的，逻辑大部分还是没变，需要细节的请移步开头的链接，博文中思路细节大神讲的很明白。
说下我添加的功能及优化的地方：

• 点击按钮自动滚动一格：原来的滚动实现是基于触摸事件+记录滑动距离，因此自动滚动也基于一样的逻辑：主动调用触摸方法模拟触摸事件。
• 原博文存在瞬滑时回滚很多造成不友好现象，修复是在ACTION_UP时通过计算矫正滑动位置和data item的对应关系。

下面上代码。

package com.example.wheelview;
import android.animation.Animator;
import android.animation.AnimatorListenerAdapter;
import android.animation.ValueAnimator;
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 android.view.animation.LinearInterpolator;
import java.util.ArrayList;
import java.util.List;
/** * 滚动选择器,https://blog.csdn.net/zhongkejingwang/article/details/38513301 * * @author huanghp */
public class PickerView extends View {
public static final String TAG = "PickerView";
//minTextSize和text之间间距之比
public static final float MARGIN_ALPHA = 1.56f;
//自动回滚到中间的速度
public static final byte SPEED = 2;
public static final byte PERIOD = 10;
public static final byte CODE = 0X10;
private List<String> 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 = 48;
private float mMinTextSize = 32;
private float mMaxTextAlpha = 255;
private float mMinTextAlpha = 120;
private int mColorText = 0xffffff;
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 volatile boolean isInAnimate;
private Handler updateHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
if (Math.abs(mMoveLen) < SPEED) {
mMoveLen = 0;
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;
sendEmptyMessageDelayed(CODE, PERIOD);
}
invalidate();
}
};
public PickerView(Context context) {
this(context, null);
}
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) {
if (datas != null) {
mDataList.addAll(datas);
}
mCurrentSelected = mDataList.size() / 2;
performSelect();
invalidate();
}
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() {
mDataList = new ArrayList<>();
mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaint.setStyle(Style.FILL);
mPaint.setTextAlign(Align.CENTER);
mPaint.setColor(mColorText);
// mPaint.setTypeface(Typeface.create("eurostile", Typeface.NORMAL));
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
if (isInit) drawData(canvas);
}
private void drawData(Canvas canvas) {
if (mDataList.isEmpty()) return;
// 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));//这里是经过简化后的公式
canvas.drawText(mDataList.get(mCurrentSelected), 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));
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) {
updateHandler.removeMessages(CODE);
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;
}
//这段是为了修正瞬滑导致回滚较多现象，屏蔽亦可
if (Math.abs(mMoveLen) > MARGIN_ALPHA * mMinTextSize / 2) {
int m = (int) (Math.abs(mMoveLen) / (MARGIN_ALPHA * mMinTextSize / 2));
for (int i = 0; i < m; i++) {
if (mMoveLen > 0) moveTailToHead();
else moveHeadToTail();
}
if (mMoveLen > 0) mMoveLen -= MARGIN_ALPHA * mMinTextSize * m / 2;
else mMoveLen += MARGIN_ALPHA * mMinTextSize * m / 2;
}
updateHandler.removeMessages(CODE);
updateHandler.sendEmptyMessage(CODE);
}
/** * @param up 是否向上滑动 */
public void autoScroll(boolean up) {
if (isInAnimate) return;
isInAnimate = true;
final float[] values = up ? new float[]{MARGIN_ALPHA * mMinTextSize + 1, 0} : new float[]{0, MARGIN_ALPHA * mMinTextSize + 1};
ValueAnimator va = ValueAnimator.ofFloat(values);
va.setDuration(100);
va.setInterpolator(new LinearInterpolator());
va.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
@Override
public void onAnimationUpdate(ValueAnimator animation) {
float v = (float) animation.getAnimatedValue();
doMove(MotionEvent.obtain(System.currentTimeMillis(), 0, 0, 0f, v, 0));
}
});
va.addListener(new AnimatorListenerAdapter() {
@Override
public void onAnimationEnd(Animator animation) {
doUp(null);
isInAnimate = false;
}
@Override
public void onAnimationStart(Animator animation) {
doDown(MotionEvent.obtain(System.currentTimeMillis(), 0, 0, 0f, values[0], 0));
}
});
va.start();
}
public interface onSelectListener {
void onSelect(String text);
}
}

谢谢！

本文地址：https://blog.csdn.net/u014763302/article/details/108171993