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：
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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);
}
}
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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：
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<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>
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两个pickerview两个textview，很简单。
下面是mainactivity的代码：
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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;
}
}
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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。