最近项目用到滚动选择器，网上找了很多，效果都不是很好，其中一个还不可以，但是没有fling效果，于是就自己动手改了改。
总共就一个自定义View，一个文件解决。
public class StringPicker extends View {
/** 自动回滚到中间的速度 */
private static final float SPEED = 2;
private List<String> dataList = new ArrayList<>();
/** 选中的位置，这个位置是dataList的中心位置，一直不变 */
private int currentSelected;
private Paint paint;
private float selectedTextSize = -1;
private float normalTextSize = -1;
private float textSpace = -1;
private int selectedTextColor = 0xFF00839A;
private int normalTextColor = 0x66666666;
private int height;
private int width;
private float lastDownY;
/** 滑动的距离 */
private float moveLen = 0;
private boolean isInit = false;
private onSelectListener selectListener;
private Timer timer;
private MyTimerTask task;
private GestureDetector gestureDetector;
private Scroller scroller;
private boolean isFling;
public StringPicker(Context context) {
this(context, null);
}
public StringPicker(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
private void init() {
timer = new Timer();
paint = new Paint(Paint.ANTI_ALIAS_FLAG);
paint.setStyle(Paint.Style.FILL);
paint.setTextAlign(Paint.Align.CENTER);
gestureDetector = new GestureDetector(getContext(), new GestureDetector.SimpleOnGestureListener() {
@Override
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
isFling = true;
scroller.fling((int) e2.getX(), (int) e2.getY(), 0, (int)velocityY, 0, 0, -2000, 2000);
return super.onFling(e1, e2, velocityX, velocityY);
}
});
scroller = new Scroller(getContext());
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
height = getHeight();
width = getWidth();
if (selectedTextSize == -1 || normalTextSize == -1) {
selectedTextSize = height / 3f;
normalTextSize = selectedTextSize / 2f;
}
if (textSpace == -1) textSpace = normalTextSize * 1.7f;
isInit = true;
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
// 根据index绘制view
if (isInit)
drawData(canvas);
}
@Override
public void computeScroll() {
if (scroller.computeScrollOffset()) {
if (isFling) doMove(null);
} else {
if (isFling) {
doUp(null);
isFling = false;
}
}
}
public void setOnSelectListener(onSelectListener listener) {
selectListener = listener;
}
public void setTextColor(int selectedTextColor, int normalTextColor) {
this.selectedTextColor = selectedTextColor;
this.normalTextColor = normalTextColor;
postInvalidate();
}
public void setTextSize(float selectedTextSize, float normalTextSize) {
this.selectedTextSize = selectedTextSize;
this.normalTextSize = normalTextSize;
postInvalidate();
}
/**字体间距，指未选中字体间距*/
public void setTextSpace(float space) {
textSpace = space;
}
public void setTypeface(Typeface typeface) {
paint.setTypeface(typeface);
postInvalidate();
}
private void performSelect() {
if (selectListener != null)
selectListener.onSelect(dataList.get(currentSelected));
}
public void setData(List<String> dataList) {
if (dataList == null || dataList.size() == 0) return;
this.dataList = dataList;
currentSelected = dataList.size() / 2;
postInvalidate();
}
/**
* 选择选中的item的index
*/
public void setSelected(String item) {
for (int i = 0; i < dataList.size(); i++) {
if (dataList.get(i).equals(item)) {
currentSelected = i;
}
}
int distance = dataList.size() / 2 - currentSelected;
if (distance < 0) {
for (int i = 0; i < -distance; i++) {
moveHeadToTail();
currentSelected--;
}
} else if (distance > 0) {
for (int i = 0; i < distance; i++) {
moveTailToHead();
currentSelected++;
}
}
performSelect();
postInvalidate();
}
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(height / 4.0f, moveLen);
float size = (selectedTextSize - normalTextSize) * scale + normalTextSize;
paint.setTextSize(size);
paint.setColor(getColor(scale));
// 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 = width / 2f;
float y = height / 2f + moveLen;
Paint.FontMetricsInt fmi = paint.getFontMetricsInt();
float baseline = y - (fmi.bottom / 2f + fmi.top / 2f);
int indexs = currentSelected;
String textData = dataList.get(indexs);
canvas.drawText(textData, x, baseline, paint);
// 绘制上方data
for (int i = 1; (currentSelected - i) >= 0; i++) {
drawOtherText(canvas, i, -1);
}
// 绘制下方data
for (int i = 1; (currentSelected + i) < dataList.size(); i++) {
drawOtherText(canvas, i, 1);
}
}
/**
* @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 = textSpace * position + type * moveLen;
float scale = parabola(height / 4.0f, d);
float size = (selectedTextSize - normalTextSize) * scale + normalTextSize;
paint.setTextSize(size);
paint.setColor(getColor(scale));
float y = (float) (height / 2.0 + type * d);
Paint.FontMetricsInt fmi = paint.getFontMetricsInt();
float baseline = (float) (y - (fmi.bottom / 2.0 + fmi.top / 2.0));
int indexs = currentSelected + type * position;
String textData = dataList.get(indexs);
canvas.drawText(textData, (float) (width / 2.0), baseline, paint);
}
private int getColor(float scale) {
int Aa = normalTextColor >> 24 & 0xff;
int Ra = normalTextColor >> 16 & 0xff;
int Ga = normalTextColor >> 8 & 0xff;
int Ba = normalTextColor & 0xff;
int Ab = selectedTextColor >> 24 & 0xff;
int Rb = selectedTextColor >> 16 & 0xff;
int Gb = selectedTextColor >> 8 & 0xff;
int Bb = selectedTextColor & 0xff;
int a = (int) (Aa + (Ab - Aa) * scale);
int r = (int) (Ra + (Rb - Ra) * scale);
int g = (int) (Ga + (Gb - Ga) * scale);
int b = (int) (Ba + (Bb - Ba) * scale);
return Color.argb(a, r, g, b);
}
/**
* 抛物线
* @param zero 零点坐标
* @param x 偏移量
*/
private float parabola(float zero, float x) {
float f = (float) (1 - Math.pow(x / zero, 2));
return f < 0 ? 0 : f;
}
private void moveHeadToTail() {
dataList.add(dataList.remove(0));
}
private void moveTailToHead() {
dataList.add(0, dataList.remove(dataList.size() - 1));
}
@Override
public boolean onTouchEvent(MotionEvent event) {
gestureDetector.onTouchEvent(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(!scroller.isFinished()) {
scroller.abortAnimation();
}
if (task != null) {
task.cancel();
task = null;
}
lastDownY = event.getY();
}
private void doMove(MotionEvent event) {
float currY;
if (event == null) {
currY = scroller.getCurrY();
} else {
currY = event.getY();
}
moveLen += currY - lastDownY;
if (moveLen > textSpace / 2) {
// 往下滑超过离开距离
moveTailToHead();
moveLen = moveLen - textSpace;
} else if (moveLen < -textSpace / 2) {
// 往上滑超过离开距离
moveHeadToTail();
moveLen = moveLen + textSpace;
}
lastDownY = currY;
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(moveLen) < 0.0001) {
moveLen = 0;
return;
}
if (task != null) {
task.cancel();
task = null;
}
task = new MyTimerTask(updateHandler);
timer.schedule(task, 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);
}
final Handler updateHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
if (Math.abs(moveLen) < SPEED) {
moveLen = 0;
if (task != null) {
task.cancel();
task = 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
moveLen = moveLen - moveLen / Math.abs(moveLen) * SPEED;
invalidate();
}
};
}布局文件：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.zfs.stringpicker.MainActivity">
<com.zfs.stringpicker.StringPicker
android:id="@+id/string_picker"
android:layout_width="match_parent"
android:layout_height="200dp"/>
</RelativeLayout>MainActivity中使用：
public class MainActivity extends AppCompatActivity {
private Toast toast;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
toast = Toast.makeText(this, "", Toast.LENGTH_SHORT);
StringPicker stringPicker = (StringPicker) findViewById(R.id.string_picker);
List<String> list = new ArrayList<>();
for (int i = 1900; i <= 2016; i++) {
list.add(String.valueOf(i));
}
stringPicker.setData(list);
try {
stringPicker.setTypeface(Typeface.createFromAsset(getAssets(), "slender.ttf"));
} catch (Exception e){
e.printStackTrace();
}
//滚动监听
stringPicker.setOnSelectListener(new StringPicker.onSelectListener() {
@Override
public void onSelect(String text) {
toast.setText(text);
toast.show();
}
});
}
}