Android自定义View圆形图片控件代码详解

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public class CircleView extends View {

  private static final int DEFAULT_SIZE = 200;

  private static final int DEFAULT_RADIUS = 20;

  private static final int TYPE_ROUND = 1;

  private static final int TYPE_RECT = 2;

  private int mSize;

  private int mResourceId;

  private int mType;

  private Paint mPaint;

  private Bitmap mSrcBitmap;

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

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

  public CircleView(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    TypedArray ta = context.obtainStyledAttributes(attrs, R.styleable.CircleView);
    mResourceId = ta.getResourceId(R.styleable.CircleView_src, R.mipmap.ic_launcher);
    mType = ta.getInt(R.styleable.CircleView_type, TYPE_ROUND);
    ta.recycle();
    init();
  }

  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    int width = getMeasureSize(widthMeasureSpec);
    int height = getMeasureSize(heightMeasureSpec);
    mSize = Math.min(width, height);
    setMeasuredDimension(mSize, mSize);
  }

  @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    //绘制背景
    if (mSrcBitmap == null) {
      mSrcBitmap = getScaleBitmap();
    }
    if (mType == TYPE_ROUND) {
      canvas.drawCircle(mSize / 2, mSize / 2, mSize / 2, mPaint);
    } else if (mType == TYPE_RECT) {
      canvas.drawRoundRect(0, 0, mSize, mSize, DEFAULT_RADIUS, DEFAULT_RADIUS, mPaint);
    }
    //设置模式为:显示背景层和上层的交集，且显示上层图像
    mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
    //绘制要显示的图像
    canvas.drawBitmap(mSrcBitmap, 0, 0, mPaint);
    //重置Xfermode
    mPaint.setXfermode(null);
  }

  private void init() {
    //禁用硬件加速,否则可能无法绘制圆形
    setLayerType(LAYER_TYPE_HARDWARE, null);
    mPaint = new Paint();
    mPaint.setAntiAlias(true);
    mPaint.setStyle(Paint.Style.FILL);
  }

  private int getMeasureSize(int measureSpec) {
    int mode = MeasureSpec.getMode(measureSpec);
    int size = MeasureSpec.getSize(measureSpec);
    return mode == MeasureSpec.EXACTLY &＃63; size : DEFAULT_SIZE;
  }

  /**
   * 获取缩放后的Bitmap
   *
   * @return
   */
  private Bitmap getScaleBitmap() {
    BitmapFactory.Options optiOns= new BitmapFactory.Options();
    options.inJustDecodeBounds = true;
    BitmapFactory.decodeResource(getResources(), mResourceId, options);
    options.inSampleSize = calcSampleSize(options, mSize, mSize);
    options.inJustDecodeBounds = false;
    return BitmapFactory.decodeResource(getResources(), mResourceId, options);
  }

  /**
   * 计算缩放比例
   *
   * @param option
   * @param width
   * @param height
   * @return
   */
  private int calcSampleSize(BitmapFactory.Options option, int width, int height) {
    int originWidth = option.outWidth;
    int originHeight = option.outHeight;
    int sampleSize = 1;
    while ((originWidth = originWidth >> 1) > width && (originHeight = originHeight >> 1) > height) {
      sampleSize = sampleSize <<1;
    }
    return sampleSize;
  }
}

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