最近有个做产品的时候有个新需求，要求recylerview中的item为圆形，并且点击后，有选中效果的边框。具体效果如下图：

效果一.jpeg

效果二.jpeg

所以我在recylerview的item中自定义了imageview，实现图片的圆形显示，并且点击的时候，显示圆形边框，边框颜色也可以自己设置。直接上代码

public class CircleImageView extends
android.support.v7.widget.AppCompatImageView {

private Paint mPaint;
private Paint mPaint2;
private BitmapShader mBitmapShader;

int bw = 0;
int bh = 0;

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

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

public CircleImageView(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    init();
}

private void init() {
    mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    mPaint.setStyle(Paint.Style.FILL);

    mPaint2 = new Paint(Paint.ANTI_ALIAS_FLAG);
    mPaint2.setStyle(Paint.Style.STROKE);
    mPaint2.setStrokeWidth(4);
    mPaint2.setColor(mBorderColor);
}

@Override
public void setImageDrawable(Drawable drawable)
{
    super.setImageDrawable(drawable);
    Bitmap bmp = getBitmapFromDrawable(drawable);
    if(bmp!=null) {
        mBitmapShader = new BitmapShader(bmp , Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);
        mPaint.setShader(mBitmapShader);
        bw = bmp.getWidth();
        bh = bmp.getHeight();
    }else{
        mBitmapShader = null;
    }
}

private Bitmap getBitmapFromDrawable(Drawable drawable)
{
    if (drawable == null) return null;
    if (drawable instanceof BitmapDrawable)
        return ((BitmapDrawable) drawable).getBitmap();
    try
    {
        Bitmap bitmap;
        if (drawable instanceof ColorDrawable) {
            bitmap = Bitmap.createBitmap(2, 2, Bitmap.Config.ARGB_8888);
        }else {
            bitmap = Bitmap.createBitmap(drawable.getIntrinsicWidth(),
                    drawable.getIntrinsicHeight(),
                    Bitmap.Config.ARGB_8888);
        }
        bw = bitmap.getWidth();
        bh = bitmap.getHeight();
        return bitmap;
    }
    catch (OutOfMemoryError e)
    {
        return null;
    }
}

@Override
public void setImageBitmap(Bitmap bm)
{
    super.setImageBitmap(bm);
    if(bm!=null && !bm.isRecycled()) {
        mBitmapShader = new BitmapShader(bm, Shader.TileMode.CLAMP,
                Shader.TileMode.CLAMP);
        mPaint.setShader(mBitmapShader);
    }else{
        mBitmapShader = null;
    }
}

@RequiresApi(api = Build.VERSION_CODES.JELLY_BEAN)
@Override
protected void onDraw(Canvas canvas)
{
    if (getDrawable() == null) return;
    final int saveCount = canvas.getSaveCount();
    canvas.save();
    if (getCropToPadding()) {
        final int scrollX = getScrollX();
        final int scrollY = getScrollY();
        canvas.clipRect(scrollX + getPaddingLeft(), scrollY + getPaddingTop(),
                scrollX + getRight() - getLeft() - getPaddingRight(),
                scrollY + getBottom() - getTop() - getPaddingBottom());
    }
    canvas.translate(getPaddingLeft(), getPaddingTop());

    if (getImageMatrix() != null && mBitmapShader!=null)
    {
        mBitmapShader.setLocalMatrix(getImageMatrix());
    }
    int h = getMeasuredHeight() - getPaddingTop() - getPaddingBottom();
    int w = getMeasuredWidth() - getPaddingLeft() - getPaddingRight();
    float radius = h > w ? w >>> 1 : h >>> 1;
    canvas.drawCircle(w >>> 1, h >>> 1, radius, mPaint);
    canvas.restoreToCount(saveCount);
    if(isShowBorder){
        canvas.translate(getPaddingLeft(), getPaddingTop());
        canvas.drawCircle(w >>> 1, h >>> 1, radius, mPaint2);
        canvas.translate(-1*getPaddingLeft(), -1*getPaddingTop());
    }
}

@Override
public void setPadding(int left, int top, int right, int bottom) {
    super.setPadding(left, top, right, bottom);
    invalidate();
}

private int mBorderColor = 0xffff0000;
private boolean isShowBorder = false;
public void setBorderColor(int borderColor) {
    mBorderColor = borderColor;
    mPaint2.setColor(mBorderColor);
}

public void setShowBorder(boolean isShow) {
    isShowBorder = isShow;
    invalidate();
}
}

然后就可以正常在item的xml文件中写入就可以了，但是需要注意的是一定要设置padding这个属性，否则边框显示不出来。如下：

 android:padding="1dp"

然后就是使用的方法了，设置边框颜色的方法：

mImageView.setBorderColor(Color.parseColor("#24c789"));

设置是否显示边框的方法：

mImageView.setShowBorder(true);