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,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),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,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
源码下载：PickerView滚动选择器
希望本文对大家学习滚动选择器PickerVIEw有所帮助。
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