项目中用到一个比较觉得不错的控件：WheelView，即上下滚动View。它是继承ScrollView实现，在Android各版本上的效果都是如下：也许在git上有许多这样功能的控件，但个人认为这个控件实现的方式简单，比较让人容易理解，对自定义控件的实现有借鉴意义，故在此做个记录。
代码如下：
public class WheelView extends ScrollView {
public static final String TAG = WheelView.class.getSimpleName();
public static class OnWheelViewListener {
public void onSelected(int selectedIndex, String item) {
}
}
private Context context;
private LinearLayout views;
public WheelView(Context context) {
super(context);
init(context);
}
public WheelView(Context context, AttributeSet attrs) {
super(context, attrs);
init(context);
}
public WheelView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init(context);
}
List<String> items;
private List<String> getItems() {
return items;
}
public void setItems(List<String> list) {
if (null == items) {
items = new ArrayList<String>();
}
items.clear();
items.addAll(list);
// 前面和后面补全
for (int i = 0; i < offset; i++) {
items.add(0, "");
items.add("");
}
initData();
}
public static final int OFF_SET_DEFAULT = 1;
int offset = OFF_SET_DEFAULT; // 偏移量（需要在最前面和最后面补全）
public int getOffset() {
return offset;
}
public void setOffset(int offset) {
this.offset = offset;
}
int displayItemCount; // 每页显示的数量
int selectedIndex = 1;
private void init(Context context) {
this.context = context;
Log.d(TAG, "parent: " + this.getParent());
this.setVerticalScrollBarEnabled(false);
views = new LinearLayout(context);
views.setOrientation(LinearLayout.VERTICAL);
this.addView(views);
scrollerTask = new Runnable() {
public void run() {
int newY = getScrollY();
if (initialY - newY == 0) { // stopped
final int remainder = initialY % itemHeight;
final int divided = initialY / itemHeight;
if (remainder == 0) {
selectedIndex = divided + offset;
onSeletedCallBack();
} else {
if (remainder > itemHeight / 2) {
WheelView.this.post(new Runnable() {
@Override
public void run() {
WheelView.this.smoothScrollTo(0, initialY - remainder + itemHeight);
selectedIndex = divided + offset + 1;
onSeletedCallBack();
}
});
} else {
WheelView.this.post(new Runnable() {
@Override
public void run() {
WheelView.this.smoothScrollTo(0, initialY - remainder);
selectedIndex = divided + offset;
onSeletedCallBack();
}
});
}
}
} else {
initialY = getScrollY();
WheelView.this.postDelayed(scrollerTask, newCheck);
}
}
};
// 默认初始不滑动时执行一次回调
if (null != onWheelViewListener) {
onWheelViewListener.onSelected(selectedIndex, items.get(selectedIndex));
}
}
int initialY;
Runnable scrollerTask;
int newCheck = 50;
public void startScrollerTask() {
initialY = getScrollY();
this.postDelayed(scrollerTask, newCheck);
}
private void initData() {
displayItemCount = offset * 2 + 1;
views.removeAllViews();
for (String item : items) {
views.addView(createView(item));
}
refreshItemView(0);
}
int itemHeight = 0;
private TextView createView(String item) {
TextView tv = new TextView(context);
tv.setLayoutParams(new LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT));
tv.setSingleLine(true);
tv.setTextSize(TypedValue.COMPLEX_UNIT_SP, 20);
tv.setText(item);
tv.setGravity(Gravity.CENTER);
int padding = dip2px(15);
tv.setPadding(padding, padding, padding, padding);
if (0 == itemHeight) {
itemHeight = getViewMeasuredHeight(tv);
Log.d(TAG, "itemHeight: " + itemHeight);
views.setLayoutParams(new LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, itemHeight * displayItemCount, Gravity.CENTER_HORIZONTAL));
views.setGravity(Gravity.CENTER);
LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams) this.getLayoutParams();
this.setLayoutParams(new LinearLayout.LayoutParams(lp.width, itemHeight * displayItemCount));
}
return tv;
}
@Override
protected void onScrollChanged(int l, int t, int oldl, int oldt) {
super.onScrollChanged(l, t, oldl, oldt);
refreshItemView(t);
if (t > oldt) {
// Log.d(TAG, "向下滚动");
scrollDirection = SCROLL_DIRECTION_DOWN;
} else {
// Log.d(TAG, "向上滚动");
scrollDirection = SCROLL_DIRECTION_UP;
}
}
private void refreshItemView(int y) {
int position = y / itemHeight + offset;
int remainder = y % itemHeight;
int divided = y / itemHeight;
if (remainder == 0) {
position = divided + offset;
} else {
if (remainder > itemHeight / 2) {
position = divided + offset + 1;
}
}
int childSize = views.getChildCount();
for (int i = 0; i < childSize; i++) {
TextView itemView = (TextView) views.getChildAt(i);
if (null == itemView) {
return;
}
if (position == i) {
itemView.setTextColor(context.getResources().getColor(R.color.colorAccent));
} else {
itemView.setTextColor(context.getResources().getColor(R.color.colorPrimaryDark));
}
}
}
/**
* 获取选中区域的边界
*/
int[] selectedAreaBorder;
private int[] obtainSelectedAreaBorder() {
if (null == selectedAreaBorder) {
selectedAreaBorder = new int[2];
selectedAreaBorder[0] = itemHeight * offset;
selectedAreaBorder[1] = itemHeight * (offset + 1);
}
return selectedAreaBorder;
}
private int scrollDirection = -1;
private static final int SCROLL_DIRECTION_UP = 0;
private static final int SCROLL_DIRECTION_DOWN = 1;
Paint paint;
int viewWidth;
@Override
public void setBackgroundDrawable(Drawable background) {
if (viewWidth == 0) {
// viewWidth = ((Activity) context).getWindowManager().getDefaultDisplay().getWidth();
viewWidth = views.getWidth();
Log.d(TAG, "viewWidth: " + viewWidth);
}
if (null == paint) {
paint = new Paint();
paint.setColor(Color.parseColor("#83cde6"));
paint.setStrokeWidth(dip2px(1f));
}
background = new Drawable() {
@Override
public void draw(Canvas canvas) {
canvas.drawLine(viewWidth * 1 / 6, obtainSelectedAreaBorder()[0], viewWidth * 5 / 6, obtainSelectedAreaBorder()[0], paint);
canvas.drawLine(viewWidth * 1 / 6, obtainSelectedAreaBorder()[1], viewWidth * 5 / 6, obtainSelectedAreaBorder()[1], paint);
}
@Override
public void setAlpha(int alpha) {
}
@Override
public void setColorFilter(ColorFilter cf) {
}
@Override
public int getOpacity() {
return PixelFormat.UNKNOWN;
}
};
super.setBackgroundDrawable(background);
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
Log.d(TAG, "w: " + w + ", h: " + h + ", oldw: " + oldw + ", oldh: " + oldh);
setBackgroundDrawable(null);
}
/**
* 选中回调
*/
private void onSeletedCallBack() {
if (null != onWheelViewListener) {
onWheelViewListener.onSelected(selectedIndex, items.get(selectedIndex));
}
}
public void setSeletion(int position) {
final int p = position;
selectedIndex = p + offset;
this.post(new Runnable() {
@Override
public void run() {
WheelView.this.smoothScrollTo(0, p * itemHeight);
}
});
}
public String getSeletedItem() {
return items.get(selectedIndex);
}
public int getSeletedIndex() {
return selectedIndex - offset;
}
@Override
public void fling(int velocityY) {
super.fling(velocityY / 3);
}
@Override
public boolean onTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_UP) {
startScrollerTask();
}
return super.onTouchEvent(ev);
}
private OnWheelViewListener onWheelViewListener;
public OnWheelViewListener getOnWheelViewListener() {
return onWheelViewListener;
}
public void setOnWheelViewListener(OnWheelViewListener onWheelViewListener) {
this.onWheelViewListener = onWheelViewListener;
// 默认初始不滑动时执行一次回调
onWheelViewListener.onSelected(selectedIndex, items.get(selectedIndex));
}
private int dip2px(float dpValue) {
final float scale = context.getResources().getDisplayMetrics().density;
return (int) (dpValue * scale + 0.5f);
}
private int getViewMeasuredHeight(View view) {
int width = View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED);
int expandSpec = View.MeasureSpec.makeMeasureSpec(Integer.MAX_VALUE >> 2,
View.MeasureSpec.AT_MOST);
view.measure(width, expandSpec);
return view.getMeasuredHeight();
}
}
MainActivity代码：
public class MainActivity extends AppCompatActivity {
private TextView mTvYear;
private List<String> mList = new ArrayList<>();
private String mSelectText = "";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mTvYear = findViewById(R.id.tv_year);
mTvYear.setOnClickListener(mClickListener);
for (int i = 10; i <= 99; i++) {
mList.add(String.format("%d后", i));
}
}
private void showDialog(TextView textView, List<String> list, int selected) {
showChoiceDialog(list, textView, selected,
new WheelView.OnWheelViewListener() {
@Override
public void onSelected(int selectedIndex, String item) {
mSelectText = item;
}
});
}
private void showChoiceDialog(List<String> mList, final TextView textView, int selected, WheelView.OnWheelViewListener listener) {
mSelectText = "";
View view = LayoutInflater.from(this).inflate(R.layout.item, null);
WheelView wheelView = view.findViewById(R.id.wheel);
wheelView.setOffset(2);
wheelView.setSeletion(selected);
wheelView.setItems(mList);
wheelView.setOnWheelViewListener(listener);
AlertDialog alertDialog = new AlertDialog.Builder(this)
.setView(view)
.setPositiveButton("确认", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
textView.setText(mSelectText);
textView.setTextColor(getResources().getColor(R.color.colorPrimaryDark));
}
}).create();
alertDialog.show();
}
private View.OnClickListener mClickListener = new View.OnClickListener() {
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.tv_year:
showDialog(mTvYear, mList, 40);
break;
}
}
};
}
item布局文件：
<com.example.demo.WheelView
android:id="@+id/wheel"
android:layout_width="match_parent"
android:layout_height="40dp" />
-
首先WheelView继承ScrollView，这样就很好的解决了上下滚动的问题。
-
WheelView里面add了一个 LinearLayout作为它的唯一子View。LinearLayout竖向排列，当调用setItems(List<String> list) 的时候就是给Linearlayout添加一个个的子view，竖向排列，并设置Linearlayout和WheelView的高度为3个Item的高度。
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当所有的Item都添加完后，会触发protected void onSizeChanged(int w, int h, int oldw, int oldh)，在这里设置WheelView的背景，也就是夹着中间Item的上下两根蓝色线。
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在onTouchEvent(MotionEvent ev)方法中，当手指抬起的时候处理移动的距离不是一个Item高度的整数倍的情况，让Linearlayout缓慢滚动的位置上。
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最后onScrollChanged(int l, int t, int oldl, int oldt)方法处理每个Item的字体的颜色。
