Android自定义控件View（二）继承控件

在前一篇博客中学习了Android自定义控件View的流程步骤和注意点，不了解的童鞋可以参考Android自定义控件View（一）。这一节开始学习自定义控件View（二）之继承系统已有的控件。我们来自定义一个圆形ImageView。

RoundImageView

随着Android UI效果越来越炫，很多系统自带的控件已经无法满足日常开发需求，比如很多应用的头像是圆形的，QQ头像就是圆形的图片。但是Android系统提供的控件当中没有一个是圆形的。那么怎么才能实现圆形头像效果呢？两种方法：

• 图片直接做成圆形的
• 自定义一个圆形的view控件来加载图片

第一种方法有局限性，因为大多数图片都是矩形的，也无法确保用户提供的图片是圆形的。因此此方法直接放弃。
第二种方法就是我们经常使用的，继承ImageView重新自定义一个RoundImageView。

根据自定义控件View的流程，我们一步一步来实现RoundImageView吧。

1.自定义attrs.xml属性文件

<--圆形轮廓的宽度-->
 <attr name="border_thickness" format="dimension"></attr>
 <--圆形轮廓外边框的颜色-->
 <attr name="border_outside_color" format="color"></attr>
 <--圆形轮廓内边框的颜色-->
 <attr name="border_inside_color" format="color"></attr>

2.获取View的属性值

 private void setCustomAttributes(AttributeSet attrs) {
        TypedArray a = mContext.obtainStyledAttributes(attrs,
                R.styleable.RoundImageView);
        mBorderThickness = a.getDimensionPixelSize(
                R.styleable.RoundImageView_border_thickness, 0);
        mBorderOutsideColor = a
                .getColor(R.styleable.RoundImageView_border_outside_color,
                        defaultColor);
        mBorderInsideColor = a.getColor(
                R.styleable.RoundImageView_border_inside_color, defaultColor);
        a.recycle();
    }

可以看到，我们这里自定义了3个属性，因为RoundImageViwe控件是继承自ImageView的，所以继承了ImageView所有的属性和方法，因此，RoundImageView可以使用ImageView的一切属性。
3.重写onDraw方法

    @Override
    protected void onDraw(Canvas canvas) {
        Drawable drawable = getDrawable();
        if (drawable == null) {
            return;
        }

        if (getWidth() == 0 || getHeight() == 0) {
            return;
        }
        this.measure(0, 0);
        if (drawable.getClass() == NinePatchDrawable.class) {
            return;
        }
        Bitmap b = ((BitmapDrawable) drawable).getBitmap();
        Bitmap bitmap = b.copy(Bitmap.Config.ARGB_8888, true);

        int radius = getRadius(canvas);

        Bitmap roundBitmap = getCroppedRoundBitmap(bitmap, radius);
        canvas.drawBitmap(roundBitmap, requestWH / 2 - radius, requestWH
                / 2 - radius, null);
    }

根据控件的布局大小，获得圆形图片的半径值大小，然后根据图片的半径大小裁剪出圆形图片，最后canvas.drawBitmap画出圆形图片。

最后贴出所有代码

package com.xjp.customview;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.Rect;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.graphics.drawable.NinePatchDrawable;
import android.util.AttributeSet;
import android.util.Log;
import android.widget.ImageView;

/**
 * Description:圆形ImageView，可设置最多两个宽度不同且颜色不同的圆形边框。
 * User: xjp
 * Date: 2015/5/28
 * Time: 16:24
 */

public class RoundImageView extends ImageView {

    private static final String TAG = "RoundImageView";
    private static final boolean DEBUG = true;
    private int mBorderThickness = 0;
    private Context mContext;
    private int defaultColor = 0xFFFFFFFF;
    // 如果只有其中一个有值，则只画一个圆形边框
    private int mBorderOutsideColor = 0;
    private int mBorderInsideColor = 0;
    // 控件默认长、宽
    private int defaultWidth = 0;
    private int defaultHeight = 0;
    //控件画圆的宽高。
    private int requestWH = 0;

    public RoundImageView(Context context) {
        this(context, null);
    }

    public RoundImageView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public RoundImageView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        mContext = context;
        setCustomAttributes(attrs);
    }

    /**
     * 获得自定义控件属性值
     *
     * @param attrs
     */
    private void setCustomAttributes(AttributeSet attrs) {
        TypedArray a = mContext.obtainStyledAttributes(attrs,
                R.styleable.RoundImageView);
        mBorderThickness = a.getDimensionPixelSize(
                R.styleable.RoundImageView_border_thickness, 0);
        mBorderOutsideColor = a
                .getColor(R.styleable.RoundImageView_border_outside_color,
                        defaultColor);
        mBorderInsideColor = a.getColor(
                R.styleable.RoundImageView_border_inside_color, defaultColor);
        a.recycle();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        Drawable drawable = getDrawable();
        if (drawable == null) {
            return;
        }

        if (getWidth() == 0 || getHeight() == 0) {
            return;
        }
        this.measure(0, 0);
        if (drawable.getClass() == NinePatchDrawable.class) {
            return;
        }
        Bitmap b = ((BitmapDrawable) drawable).getBitmap();
        Bitmap bitmap = b.copy(Bitmap.Config.ARGB_8888, true);

        int radius = getRadius(canvas);

        Bitmap roundBitmap = getCroppedRoundBitmap(bitmap, radius);
        canvas.drawBitmap(roundBitmap, requestWH / 2 - radius, requestWH
                / 2 - radius, null);
    }

    /**
     * 获取画园的半径，并且绘制圆的外边框
     *
     * @param canvas
     * @return
     */
    private int getRadius(Canvas canvas) {
        if (defaultWidth == 0) {
            defaultWidth = getWidth();

        }
        if (defaultHeight == 0) {
            defaultHeight = getHeight();
        }
        requestWH = defaultHeight > defaultWidth ? defaultWidth : defaultHeight;

        int radius = 0;
        if (mBorderInsideColor != defaultColor
                && mBorderOutsideColor != defaultColor) {// 定义画两个边框，分别为外圆边框和内圆边框
            radius = requestWH / 2 - 2 * mBorderThickness;
            // 画内圆
            drawCircleBorder(canvas, radius + mBorderThickness / 2,
                    mBorderInsideColor);
            // 画外圆
            drawCircleBorder(canvas, radius + mBorderThickness
                    + mBorderThickness / 2, mBorderOutsideColor);
        } else if (mBorderInsideColor != defaultColor
                && mBorderOutsideColor == defaultColor) {// 定义画一个边框
            radius = requestWH / 2 - mBorderThickness;
            drawCircleBorder(canvas, radius + mBorderThickness / 2,
                    mBorderInsideColor);
        } else if (mBorderInsideColor == defaultColor
                && mBorderOutsideColor != defaultColor) {// 定义画一个边框
            radius = (defaultWidth < defaultHeight ? defaultWidth
                    : defaultHeight) / 2 - mBorderThickness;
            drawCircleBorder(canvas, radius + mBorderThickness / 2,
                    mBorderOutsideColor);
        } else {// 没有边框
            radius = requestWH / 2;
        }
        return radius;
    }

    /**
     * 获取裁剪后的圆形图片
     *
     * @param radius 半径
     */
    private static Bitmap getCroppedRoundBitmap(Bitmap bmp, int radius) {
        Bitmap scaledSrcBmp;
        int diameter = radius * 2;

        // 为了防止宽高不相等，造成圆形图片变形，因此截取长方形中处于中间位置最大的正方形图片
        int bmpWidth = bmp.getWidth();
        int bmpHeight = bmp.getHeight();
        int squareWidth = 0, squareHeight = 0;
        int x = 0, y = 0;
        Bitmap squareBitmap;
        if (DEBUG) {
            Log.d(TAG, "the Bitmap w:" + bmpWidth + " the Bitmap h:" + bmpHeight);
        }

        if (bmpHeight > bmpWidth) {// 高大于宽
            squareWidth = squareHeight = bmpWidth;
            x = 0;
            y = (bmpHeight - bmpWidth) / 2;
            // 截取正方形图片
            squareBitmap = Bitmap.createBitmap(bmp, x, y, squareWidth,
                    squareHeight);
        } else if (bmpHeight < bmpWidth) {// 宽大于高
            squareWidth = squareHeight = bmpHeight;
            x = (bmpWidth - bmpHeight) / 2;
            y = 0;
            squareBitmap = Bitmap.createBitmap(bmp, x, y, squareWidth,
                    squareHeight);
        } else {
            squareBitmap = bmp;
        }

        if (squareBitmap.getWidth() != diameter
                || squareBitmap.getHeight() != diameter) {
            scaledSrcBmp = Bitmap.createScaledBitmap(squareBitmap, diameter,
                    diameter, true);

        } else {
            scaledSrcBmp = squareBitmap;
        }
        Bitmap output = Bitmap.createBitmap(scaledSrcBmp.getWidth(),
                scaledSrcBmp.getHeight(), Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(output);

        Paint paint = new Paint();
        Rect rect = new Rect(0, 0, scaledSrcBmp.getWidth(),
                scaledSrcBmp.getHeight());

        paint.setAntiAlias(true);
        paint.setFilterBitmap(true);
        paint.setDither(true);
        canvas.drawARGB(0, 0, 0, 0);
        canvas.drawCircle(scaledSrcBmp.getWidth() / 2,
                scaledSrcBmp.getHeight() / 2, scaledSrcBmp.getWidth() / 2,
                paint);
        paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
        canvas.drawBitmap(scaledSrcBmp, rect, rect, paint);
        bmp.recycle();
        squareBitmap.recycle();
        scaledSrcBmp.recycle();
        bmp = null;
        squareBitmap = null;
        scaledSrcBmp = null;
        return output;
    }

    /**
     * 边缘画圆
     */
    private void drawCircleBorder(Canvas canvas, int radius, int color) {
        Paint paint = new Paint();
        /* 去锯齿 */
        paint.setAntiAlias(true);
        paint.setFilterBitmap(true);
        paint.setDither(true);
        paint.setColor(color);
        /* 设置paint的　style　为STROKE：空心 */
        paint.setStyle(Paint.Style.STROKE);
        /* 设置paint的外框宽度 */
        paint.setStrokeWidth(mBorderThickness);
        canvas.drawCircle(requestWH / 2, requestWH / 2, radius, paint);
    }

    /**
     * 设置外边框的宽度
     *
     * @param borderWith
     */
    public void setBorderWith(int borderWith) {
        mBorderThickness = borderWith;
    }

    /**
     * 设置外边框的颜色
     *
     * @param outsideColor
     */
    public void setBorderOutsideColor(int outsideColor) {
        mBorderOutsideColor = outsideColor;
    }

    /**
     * 设置内边框的颜色
     *
     * @param insideColor
     */
    public void setBorderInsideColor(int insideColor) {
        mBorderInsideColor = insideColor;
    }

}

4.在布局中这么使用

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:custom="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <com.xjp.customview.RoundImageView
        android:id="@+id/myCustom"
        android:layout_width="110dp"
        android:layout_height="110dp"
        android:scaleType="fitCenter"
        android:src="@drawable/image"
        custom:border_inside_color="#ff0000"
        custom:border_outside_color="@android:color/black"
        custom:border_thickness="2dp" />

</RelativeLayout>

当以下三个属性没有设置时，默认圆形图片没有外边框

custom:border_inside_color
custom:border_outside_color
custom:border_thickness

源码下载