Android自定义控件实战——滚动选择器PickerView

   转载请声明出处http://blog.csdn.net/zhongkejingwang/article/details/38513301

  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~

源码下载

来源：http://blog.csdn.net/zhongkejingwang/article/details/38513301

来自为知笔记(Wiz)