今天在做项目时遇到一个对话框弹出滚动选择器的效果，对于还是一个菜鸟的我，想了很久，于是决定用自定义PickerView来完成，话不多说直接上代码。
package com.feitong.orderMyView;
import java.util.ArrayList;
import java.util.List;
import java.util.Timer;
import java.util.TimerTask;
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;
public class PickerView 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<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 = 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 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();
}
public void setSelected(int selected) {
mCurrentSelected = selected;
}
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 / 6.0f;
mMinTextSize = mMaxTextSize / 3f;
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));
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) {
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(String text);
}
}
注意：如果想要设置字体大小就再这里改变值mMaxTextSize = mViewHeight / 6.0f;,布局文件我就不写了，但是值得提的是必须根据类对应的包名，来写布局文件