Android自定义控件实战——滚动选择器PickerView

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：

[java] view
plain copy

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：

[html] view
plain copy

<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：

[java] view
plain copy

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;

}

}