Android自定义控件实战—滚动选择器PickerView

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转载自： 中科靖的博客 

手机里设置闹钟需要选择时间，那个选择时间的控件就是滚动选择器，前几天用手机刷了MIUI，发现自带的那个时间选择器效果挺好看的，于是就自己仿写了一个，权当练手。先来看效果：

                                                                 

效果还行吧？实现思路就是自定义一个PickerView，单独滚动的是一个PickerView，显然上图中有分和秒的选择所以在布局里用了两个PickerView。由于这里不涉及到text的点击事件，所以只需要继承View就行了，直接把text用canvas画上去。PickerView的实现的主要难点：

难点1：

        字体随距离的渐变。可以看到，text随离中心位置的距离变化而变化，这里变化的是透明度alpha和字体大小TexSize，这两个值我都设置了Max和Min值，通过其与中心点的距离计算scale。我用的是变化曲线是抛物线scale=1-ax^2(x<=Height/4),scale = 0(x>Height/4)，a=(4/Height)^2。x就是距离View中心的偏移量。用图片表示如下：

难点2：

     text的居中。绘制text的时候不仅要使其在x方向上居中，还要在y方向上居中，在x方向上比较简单，设置Paint的Align为Align.CENTER就行了，但是y方向上很蛋疼，需要计算text的baseline。

难点3：

    循环滚动。为了解决循环滚动的问题我把存放text的List从中间往上下摊开，通过不断地moveHeadToTail和moveTailToHead使选中的text始终是list的中间position的值。

  

     以上就是几个难点，了解了之后可以来看PickerView的代码了：

    package com.jingchen.timerpicker;         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;         /**     * 滚动选择器     *      * @author chenjing     *      */    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 / 4.0f;            mMinTextSize = mMaxTextSize / 2f;            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);        }    }

代码里的注释都写的很清楚了。接下来，我们就用写好的PickerView实现文章开头的图片效果吧~

首先看MainActivity的布局：

    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"        android:layout_width="match_parent"        android:layout_height="match_parent"        android:background="#000000" >             <RelativeLayout            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:layout_centerInParent="true"            android:background="#ffffff" >                 <com.jingchen.timerpicker.PickerView                android:id="@+id/minute_pv"                android:layout_width="80dp"                android:layout_height="160dp" />                 <TextView                android:id="@+id/minute_tv"                android:layout_width="wrap_content"                android:layout_height="wrap_content"                android:layout_centerVertical="true"                android:layout_toRightOf="@id/minute_pv"                android:text="分"                android:textColor="#ffaa33"                android:textSize="26sp"                android:textStyle="bold" />                 <com.jingchen.timerpicker.PickerView                android:id="@+id/second_pv"                android:layout_width="80dp"                android:layout_height="160dp"                android:layout_toRightOf="@id/minute_tv" />                 <TextView                android:id="@+id/second_tv"                android:layout_width="wrap_content"                android:layout_height="wrap_content"                android:layout_centerVertical="true"                android:layout_toRightOf="@id/second_pv"                android:text="秒"                android:textColor="#ffaa33"                android:textSize="26sp"                android:textStyle="bold" />        </RelativeLayout>         </RelativeLayout>

两个PickerView两个TextView，很简单。

下面是MainActivity的代码：

    package com.jingchen.timerpicker;         import java.util.ArrayList;    import java.util.List;         import com.jingchen.timerpicker.PickerView.onSelectListener;         import android.app.Activity;    import android.os.Bundle;    import android.view.Menu;    import android.widget.TextView;    import android.widget.Toast;         public class MainActivity extends Activity    {             PickerView minute_pv;        PickerView second_pv;             @Override        protected void onCreate(Bundle savedInstanceState)        {            super.onCreate(savedInstanceState);            setContentView(R.layout.activity_main);            minute_pv = (PickerView) findViewById(R.id.minute_pv);            second_pv = (PickerView) findViewById(R.id.second_pv);            List<String> data = new ArrayList<String>();            List<String> seconds = new ArrayList<String>();            for (int i = 0; i < 10; i++)            {                data.add("0" + i);            }            for (int i = 0; i < 60; i++)            {                seconds.add(i < 10 ? "0" + i : "" + i);            }            minute_pv.setData(data);            minute_pv.setOnSelectListener(new onSelectListener()            {                     @Override                public void onSelect(String text)                {                    Toast.makeText(MainActivity.this, "选择了 " + text + " 分",                            Toast.LENGTH_SHORT).show();                }            });            second_pv.setData(seconds);            second_pv.setOnSelectListener(new onSelectListener()            {                     @Override                public void onSelect(String text)                {                    Toast.makeText(MainActivity.this, "选择了 " + text + " 秒",                            Toast.LENGTH_SHORT).show();                }            });        }             @Override        public boolean onCreateOptionsMenu(Menu menu)        {            getMenuInflater().inflate(R.menu.main, menu);            return true;        }         }

OK了，自定义自己的TimerPicker就是这么简单~.

github地址：https://github.com/jingchenUSTC/TimePicker