Android自定义实现滚动选择器

在开发的过程中，现有的控件满足不了功能的需求，这个时候就需要我们自定义控件了。最近在开发中需要实现滚动进行类别的选择，也就是我们所说的滚动选择器，这里我们自定义来实现这个功能。

实现步骤：
1、先看需要实现的效果图
2、实现自定义控件(PickerScrollView )
3、popupwindow实现类(CommonPopWindow )
4.主界面(MainActivity)
5、实体类(GetConfigReq )
6、底部弹出框布局文件

实现过程：
1、先看需要实现的效果图

2、实现自定义控件(PickerScrollView )

/**
 * 滚动选择器
 */
public class PickerScrollView extends View {

    public static final String TAG = "PickerScrollView:";
    /**
     * 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 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 = 20;
    private float mMinTextSize = 10;

    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 PickerScrollView(Context context) {
        super(context);
        init();
    }

    public PickerScrollView(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 datas) {
        mDataList = datas;
        mCurrentSelected = datas.size() / 2;
        invalidate();
    }

    /**
     * 选择选中的item的index
     *
     * @param selected
     */
    public void setSelected(int selected) {
        mCurrentSelected = selected;
        int distance = mDataList.size() / 2 - mCurrentSelected;
        if (distance < 0)
            for (int i = 0; i < -distance; i++) {
                moveHeadToTail();
                mCurrentSelected--;
            }
        else if (distance > 0)
            for (int i = 0; i < distance; i++) {
                moveTailToHead();
                mCurrentSelected++;
            }
        invalidate();
    }

    /**
     * 选择选中的内容
     *
     * @param mSelectItem
     */
    public void setSelected(String mSelectItem) {
        for (int i = 0; i < mDataList.size(); i++)
            if (mDataList.get(i).equals(mSelectItem)) {
                setSelected(i);
                break;
            }
    }

    private void moveHeadToTail() {
        GetConfigReq.DatasBean datasBean = mDataList.get(0);
        mDataList.remove(0);
        mDataList.add(datasBean);
    }

    private void moveTailToHead() {
        GetConfigReq.DatasBean datasBean = mDataList.get(mDataList.size() - 1);
        mDataList.remove(mDataList.size() - 1);
        mDataList.add(0, datasBean);
    }

    @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 / 8.0f;
        mMinTextSize = mMaxTextSize / 2f;
        isInit = true;
        invalidate();
    }

    private void init() {
        timer = new Timer();
        mDataList = new ArrayList<>();
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mPaint.setStyle(Paint.Style.FILL);
        mPaint.setTextAlign(Paint.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);
        Paint.FontMetricsInt fmi = mPaint.getFontMetricsInt();
        float baseline = (float) (y - (fmi.bottom / 2.0 + fmi.top / 2.0));

        int indexs = mCurrentSelected;
        String textData = mDataList.get(indexs).getCategoryName();
        canvas.drawText(textData, 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);
        Paint.FontMetricsInt fmi = mPaint.getFontMetricsInt();
        float baseline = (float) (y - (fmi.bottom / 2.0 + fmi.top / 2.0));

        int indexs = mCurrentSelected + type * position;
        String textData = mDataList.get(indexs).getCategoryName();
        canvas.drawText(textData, (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(GetConfigReq.DatasBean pickers);
    }
}  

3、popupwindow实现类(CommonPopWindow )

/**
 * popupwindow
 */
public class CommonPopWindow {
    private static PopupWindow mPopupWindow;
    private static Builder mBuilder;
    private static View mContentView;
    private static Window mWindow;

    public interface ViewClickListener {
        void getChildView(PopupWindow mPopupWindow, View view, int mLayoutResId);
    }

    private CommonPopWindow() {
        mBuilder = new Builder();
    }

    public static Builder newBuilder() {
        if (mBuilder == null) {
            mBuilder = new Builder();
        }
        return mBuilder;
    }

    /**
     * 获取PopupWindow宽度
     *
     * @return
     */
    public int getWidth() {
        if (mPopupWindow != null) {
            return mContentView.getMeasuredWidth();
        }
        return 0;
    }


    /**
     * 获取PopupWindow高度
     *
     * @return
     */
    public int getHeight() {
        if (mPopupWindow != null) {
            return mContentView.getMeasuredHeight();
        }
        return 0;
    }

    /**
     * 显示在控件的下方
     */
    public CommonPopWindow showDownPop(View parent) {
        if (parent.getVisibility() == View.GONE) {
            mPopupWindow.showAtLocation(parent, Gravity.NO_GRAVITY, 0, 0);
        } else {
            int[] location = new int[2];
            parent.getLocationOnScreen(location);
            if (mPopupWindow != null) {
                mPopupWindow.showAtLocation(parent, Gravity.NO_GRAVITY, location[0], location[1] + parent.getHeight());
            }
        }
        return this;
    }

    /**
     * 显示在控件的上方
     */
    public CommonPopWindow showAsUp(View view) {
        if (view.getVisibility() == View.GONE) {
            mPopupWindow.showAtLocation(view, Gravity.NO_GRAVITY, 0, 0);
        } else {
            int[] location = new int[2];
            view.getLocationOnScreen(location);
            if (mPopupWindow != null) {
                mPopupWindow.showAtLocation(view, Gravity.NO_GRAVITY, location[0], location[1] - view.getHeight());
                //方式二
//                mPopupWindow.showAsDropDown(view, 0, -(getHeight() + view.getMeasuredHeight()));
            }
        }
        return this;
    }

    /**
     * 显示在控件的左边
     */
    public CommonPopWindow showAsLeft(View view) {
        if (view.getVisibility() == View.GONE) {
            mPopupWindow.showAtLocation(view, Gravity.NO_GRAVITY, 0, 0);
        } else {
            int[] location = new int[2];
            view.getLocationOnScreen(location);
            if (mPopupWindow != null) {
                mPopupWindow.showAtLocation(view, Gravity.NO_GRAVITY, location[0] - getWidth(), location[1]);
            }
        }
        return this;
    }

    /**
     * 显示在控件右边
     */
    public CommonPopWindow showAsRight(View view) {
        if (view.getVisibility() == View.GONE) {
            mPopupWindow.showAtLocation(view, Gravity.NO_GRAVITY, 0, 0);
        } else {
            int[] location = new int[2];
            view.getLocationOnScreen(location);
            if (mPopupWindow != null) {
                mPopupWindow.showAtLocation(view, Gravity.NO_GRAVITY, location[0] + view.getWidth(), location[1]);
            }
        }
        return this;
    }

    /**
     * 显示控件下方
     *
     * @param view
     * @return
     */
    public CommonPopWindow showAsDown(View view) {
        if (mPopupWindow != null) {
            mPopupWindow.showAsDropDown(view);
        }
        return this;
    }

    /**
     * 全屏弹出
     */
    public CommonPopWindow showAsBottom(View view) {
        if (view.getVisibility() == View.GONE) {
            mPopupWindow.showAtLocation(view, Gravity.NO_GRAVITY, 0, 0);
        } else {
            int[] location = new int[2];
            view.getLocationOnScreen(location);
            if (mPopupWindow != null) {
                mPopupWindow.showAtLocation(view, Gravity.BOTTOM, 0, 0);
            }
        }
        return this;
    }

    public CommonPopWindow showAtLocation(View anchor, int gravity, int x, int y) {
        if (mPopupWindow != null) {
            mPopupWindow.showAtLocation(anchor, gravity, x, y);
        }
        return this;
    }

    /**
     * 取消
     */
    public static void dismiss() {
        if (mWindow != null) {
            WindowManager.LayoutParams params = mWindow.getAttributes();
            params.alpha = 1.0f;
            mWindow.setAttributes(params);
        }
        if (mPopupWindow != null && mPopupWindow.isShowing())
            mPopupWindow.dismiss();
    }

    /*
     * ---------------------Builder-------------------------
     */
    public static class Builder implements PopupWindow.OnDismissListener {
        private Context mContext;
        private int mLayoutResId;//布局ID
        private int mWidth, mHeight;//弹窗宽高
        private int mAnimationStyle;//动画样式
        private ViewClickListener mListener;//子View监听回调
        private Drawable mDrawable;//背景Drawable
        private boolean mTouchable = true;//是否相应touch事件
        private boolean mFocusable = true;//是否获取焦点
        private boolean mOutsideTouchable = true;//设置外部是否点击
        private boolean mBackgroundDarkEnable = false;//是否背景窗体变暗
        private float mDarkAlpha = 1.0f;//透明值

        public CommonPopWindow build(Context context) {
            this.mContext = context;
            CommonPopWindow popWindow = new CommonPopWindow();
            apply();
            if (mListener != null && mLayoutResId != 0) {
                mListener.getChildView(mPopupWindow, mContentView, mLayoutResId);
            }
            return popWindow;
        }

        private void apply() {
            if (mLayoutResId != 0) {
                mContentView = LayoutInflater.from(mContext).inflate(mLayoutResId, null);
            }
            if (mWidth != 0 && mHeight != 0) {
                mPopupWindow = new PopupWindow(mContentView, mWidth, mHeight);
            } else {
                mPopupWindow = new PopupWindow(mContentView, ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);
            }

            mPopupWindow.setTouchable(mTouchable);
            mPopupWindow.setFocusable(mFocusable);
            mPopupWindow.setOutsideTouchable(mOutsideTouchable);

            if (mDrawable != null) {
                mPopupWindow.setBackgroundDrawable(mDrawable);
            } else {
                mPopupWindow.setBackgroundDrawable(new ColorDrawable());
            }
            if (mAnimationStyle != -1) {
                mPopupWindow.setAnimationStyle(mAnimationStyle);
            }
            if (mWidth == 0 || mHeight == 0) {
                measureWidthAndHeight(mContentView);
                //如果没有设置高度的情况下，设置宽高并赋值
                mWidth = mPopupWindow.getContentView().getMeasuredWidth();
                mHeight = mPopupWindow.getContentView().getMeasuredHeight();
            }

            Activity activity = (Activity) mContext;
            if (activity != null && mBackgroundDarkEnable) {
                float alpha = (mDarkAlpha >= 0f || mDarkAlpha <= 1f) ? mDarkAlpha : 0.7f;
                mWindow = activity.getWindow();
                WindowManager.LayoutParams params = mWindow.getAttributes();
                params.alpha = alpha;
                mWindow.setAttributes(params);
            }

            mPopupWindow.setOnDismissListener(this);

            mPopupWindow.update();
        }

        @Override
        public void onDismiss() {
            dismiss();
        }

        /**
         * 测量View的宽高
         *
         * @param mContentView
         */
        private void measureWidthAndHeight(View mContentView) {
            int widthMeasureSpec = View.MeasureSpec.makeMeasureSpec((1 << 30) - 1, View.MeasureSpec.AT_MOST);
            int heightMeasureSpec = View.MeasureSpec.makeMeasureSpec((1 << 30) - 1, View.MeasureSpec.AT_MOST);
            mContentView.measure(widthMeasureSpec, heightMeasureSpec);
        }

        /**
         * 设置布局ID
         *
         * @param layoutResId
         * @return
         */
        public Builder setView(@LayoutRes int layoutResId) {
            mContentView = null;
            this.mLayoutResId = layoutResId;
            return this;
        }

        /**
         * 设置宽高
         *
         * @param width
         * @param height
         * @return
         */
        public Builder setSize(int width, int height) {
            mWidth = width;
            mHeight = height;
            return this;
        }

        /**
         * 设置背景
         *
         * @param drawable
         * @return
         */
        public Builder setBackgroundDrawable(Drawable drawable) {
            mDrawable = drawable;
            return this;
        }

        /**
         * 设置背景是否变暗
         *
         * @param darkEnable
         * @return
         */
        public Builder setBackgroundDarkEnable(boolean darkEnable) {
            mBackgroundDarkEnable = darkEnable;
            return this;
        }

        /**
         * 设置背景透明度
         *
         * @param dackAlpha
         * @return
         */
        public Builder setBackgroundAlpha(@FloatRange(from = 0.0, to = 1.0) float dackAlpha) {
            mDarkAlpha = dackAlpha;
            return this;
        }

        /**
         * 是否点击Outside消失
         *
         * @param touchable
         * @return
         */
        public Builder setOutsideTouchable(boolean touchable) {
            mOutsideTouchable = touchable;
            return this;
        }

        /**
         * 是否设置Touch事件
         *
         * @param touchable
         * @return
         */
        public Builder setTouchable(boolean touchable) {
            mTouchable = touchable;
            return this;
        }

        /**
         * 设置动画
         *
         * @param animationStyle
         * @return
         */
        public Builder setAnimationStyle(@StyleRes int animationStyle) {
            mAnimationStyle = animationStyle;
            return this;
        }

        /**
         * 是否设置获取焦点
         *
         * @param focusable
         * @return
         */
        public Builder setFocusable(boolean focusable) {
            mFocusable = focusable;
            return this;
        }

        /**
         * 设置子View点击事件回调
         *
         * @param listener
         * @return
         */
        public Builder setViewOnClickListener(ViewClickListener listener) {
            this.mListener = listener;
            return this;
        }
    }
}

4.主界面(MainActivity)

public class MainActivity extends AppCompatActivity implements View.OnClickListener,CommonPopWindow.ViewClickListener{

    private TextView click;
    private TextView text;
    private List datasBeanList;
    private String categoryName;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();
        initData();
        initListener();
    }

    private void initListener() {
        click.setOnClickListener(this);
    }

    private void initData() {
        //模拟请求后台返回数据
        String response = "{\"ret\":0,\"msg\":\"succes,\",\"datas\":[{\"ID\":\"  0\",\"categoryName\":\"\\u793e\\u56e2\",\"state\":\"1\"},{\"ID\":\"1\",\"categoryName\":\"\\u539f\\u521b\",\"state\":\"1\"},{\"ID\":\"2\",\"categoryName\":\"\\u73b0\\u8d27\",\"state\":\"1\"}]}";
        GetConfigReq getConfigReq = new Gson().fromJson(response, GetConfigReq.class);
        //0请求表示成功
        if (getConfigReq.getRet() == 0) {
            //滚动选择数据集合
            datasBeanList = getConfigReq.getDatas();
        }
    }

    private void initView() {
        click = findViewById(R.id.textClick);
        text = findViewById(R.id.text);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.textClick:
                setAddressSelectorPopup(v);
                break;
        }
    }

    /**
     * 将选择器放在底部弹出框
     * @param v
     */
    private void setAddressSelectorPopup(View v) {
        int screenHeigh = getResources().getDisplayMetrics().heightPixels;

        CommonPopWindow.newBuilder()
                .setView(R.layout.pop_picker_selector_bottom)
                .setAnimationStyle(R.style.AnimUp)
                .setBackgroundDrawable(new BitmapDrawable())
                .setSize(ViewGroup.LayoutParams.MATCH_PARENT, Math.round(screenHeigh * 0.3f))
                .setViewOnClickListener(this)
                .setBackgroundDarkEnable(true)
                .setBackgroundAlpha(0.7f)
                .setBackgroundDrawable(new ColorDrawable(999999))
                .build(this)
                .showAsBottom(v);
    }


    @Override
    public void getChildView(final PopupWindow mPopupWindow, View view, int mLayoutResId) {
        switch (mLayoutResId) {
            case R.layout.pop_picker_selector_bottom:
                TextView imageBtn = view.findViewById(R.id.img_guanbi);
                PickerScrollView addressSelector = view.findViewById(R.id.address);

                // 设置数据，默认选择第一条
                addressSelector.setData(datasBeanList);
                addressSelector.setSelected(0);

                //滚动监听
                addressSelector.setOnSelectListener(new PickerScrollView.onSelectListener() {
                    @Override
                    public void onSelect(GetConfigReq.DatasBean pickers) {
                        categoryName = pickers.getCategoryName();
                    }
                });

                //完成按钮
                imageBtn.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        mPopupWindow.dismiss();
                        text.setText(categoryName);
                    }
                });
                break;
        }
    }
}

5、实体类(GetConfigReq )

public class GetConfigReq {
    /**
     * ret : 0
     * msg : succes,
     * datas : [{"ID":"  0","categoryName":"社团","state":"1"},{"ID":"1","categoryName":"原创","state":"1"},{"ID":"2","categoryName":"现货","state":"1"}]
     */

    private int ret;
    private String msg;
    private List datas;

    public int getRet() {
        return ret;
    }

    public void setRet(int ret) {
        this.ret = ret;
    }

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }

    public List getDatas() {
        return datas;
    }

    public void setDatas(List datas) {
        this.datas = datas;
    }

    public static class DatasBean {
        /**
         * ID :   0
         * categoryName : 社团
         * state : 1
         */

        private String ID;
        private String categoryName;
        private String state;

        public String getID() {
            return ID;
        }

        public void setID(String ID) {
            this.ID = ID;
        }

        public String getCategoryName() {
            return categoryName;
        }

        public void setCategoryName(String categoryName) {
            this.categoryName = categoryName;
        }

        public String getState() {
            return state;
        }

        public void setState(String state) {
            this.state = state;
        }
    }
}

6、底部弹出框布局文件

7、到这里就实现了滚动选择器的功能，主要还是自定义控件的实现。
需要Demo的童鞋底部公众号回复："滚动选择器"即可获取。

---

以下是公众号(longxuanzhigu)，之后发布的文章会同步到该公众号，方便交流学习Android知识及分享个人爱好文章：