本篇文章给大家分享的是有关Android中怎么通过自定义View实现圆形切图效果，小编觉得挺实用的，因此分享给大家学习，希望大家阅读完这篇文章后可以有所收获，话不多说，跟着小编一起来看看吧。
实现思路
使用一个Paint,将得到的Bitmap设置成paint的Shader,设置完成后,使用Matrix调整图片至居中,使用RectF约束边框,最后完成绘制
初始化Paint,设置Shader
private void init() { getBitmapFromDrawable(); if (mBitmap == null) { return; } mShader = new BitmapShader(mBitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP); // bitmap paint mFillPaint = new Paint(); mFillPaint.setAntiAlias(true); mFillPaint.setStyle(Paint.Style.FILL); mFillPaint.setShader(mShader); // border paint mBoundPaint = new Paint(); mBoundPaint.setAntiAlias(true); mBoundPaint.setStyle(Paint.Style.STROKE); mBoundPaint.setStrokeWidth(mBorderWidth); mBoundPaint.setColor(mBorderColor); // border rectF mBorderBound.set(calculateBitmapBound()); // bitmap rectF mBitmapBound.set(calculateBitmapBound()); mBitmapBound.inset(mBorderWidth - 10, mBorderWidth - 10); updateShaderMatrix(); }获取Drawable
private Bitmap getBitmapFromDrawable() { Drawable drawable = getDrawable(); if (drawable instanceof BitmapDrawable) { mBitmap = ((BitmapDrawable) drawable).getBitmap(); mBitmapWidth = mBitmap.getWidth(); mBitmapHeight = mBitmap.getHeight(); return mBitmap; } return null; }
计算边距
private RectF calculateBitmapBound() { int availableWidth = getWidth() - getPaddingLeft() - getPaddingRight(); int availableHeight = getHeight() - getPaddingTop() - getPaddingBottom(); int sideLength = Math.min(availableWidth, availableHeight); // 可用的直径 mRadius = sideLength / 2; int left = getPaddingLeft() + (availableWidth - sideLength) / 2; int top = getPaddingTop() + (availableHeight - sideLength) / 2; Log.d(TAG, "calculateBitmapBound: left >>> " + left + " top >>> " + top + " right >>> " + (left + sideLength) + " right >>> " + top + " bottom >>> " + (top + sideLength)); return new RectF(left, top, left + sideLength, top + sideLength); }
调整Matrix,防止只显示图片边角
private void updateShaderMatrix() { float scale; float dx = 0; float dy = 0; mShaderMatrix.set(null); // 调整缩放,使图片居中 if (mBitmapWidth * mBitmapBound.height() > mBitmapBound.width() * mBitmapHeight) { scale = mBitmapBound.height() / (float) mBitmapHeight; dx = (mBitmapBound.width() - mBitmapWidth * scale) * 0.5f; } else { scale = mBitmapBound.width() / (float) mBitmapWidth; dy = (mBitmapBound.height() - mBitmapHeight * scale) * 0.5f; } Log.d(TAG, "updateShaderMatrix: scale >>> " + scale); mShaderMatrix.setScale(scale, scale); // TODO: 16-10-15 http://chroya.iteye.com/blog/713869 // 回到中心点,便于下次缩放 mShaderMatrix.postTranslate((int) (dx + 0.5f) + mBitmapBound.left, (int) (dy + 0.5f) + mBitmapBound.top); mShader.setLocalMatrix(mShaderMatrix); }onDraw
@Override protected void onDraw(Canvas canvas) { if (mBitmap == null) { super.onDraw(canvas); } Log.d(TAG, "onDraw: centerX >>> " + mBitmapBound.centerX() + " centerY >>> " + mBitmapBound.centerY()); canvas.drawCircle(mBitmapBound.centerX(), mBitmapBound.centerY(), mRadius, mFillPaint); // 绘制边框 canvas.drawCircle(mBorderBound.centerX(), mBorderBound.centerY(), mRadius, mBoundPaint); }完整代码
public class CircleImageView extends ImageView { private static final String TAG = "LOGGER"; private BitmapShader mShader; private Paint mFillPaint; // 绘图 private Paint mBoundPaint; // 绘制圆边 private Bitmap mBitmap; private Drawable mDrawable; private int mBorderColor; // 边框颜色 private float mBorderWidth; // 边框宽度 private RectF mBorderBound = new RectF(); private RectF mBitmapBound = new RectF(); private Matrix mShaderMatrix = new Matrix(); private int mRadius; private int mBitmapWidth; private int mBitmapHeight; private static final float DEFAULT_BORDER_WIDTH = 5; 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); TypedArray a = getResources().obtainAttributes(attrs, R.styleable.CircleImageView); mBorderColor = a.getColor(R.styleable.CircleImageView_borderColor, Color.BLUE); mBorderWidth = a.getDimension(R.styleable.CircleImageView_borderWidth, DEFAULT_BORDER_WIDTH); mBorderWidth = a.getDimensionPixelSize(R.styleable.CircleImageView_borderWidth, 20); a.recycle(); } private void init() { getBitmapFromDrawable(); if (mBitmap == null) { return; } mShader = new BitmapShader(mBitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP); // bitmap paint mFillPaint = new Paint(); mFillPaint.setAntiAlias(true); mFillPaint.setStyle(Paint.Style.FILL); mFillPaint.setShader(mShader); // border paint mBoundPaint = new Paint(); mBoundPaint.setAntiAlias(true); mBoundPaint.setStyle(Paint.Style.STROKE); mBoundPaint.setStrokeWidth(mBorderWidth); mBoundPaint.setColor(mBorderColor); // border rectF mBorderBound.set(calculateBitmapBound()); // bitmap rectF mBitmapBound.set(calculateBitmapBound()); mBitmapBound.inset(mBorderWidth - 10, mBorderWidth - 10); updateShaderMatrix(); } @Override protected void onSizeChanged(int w, int h, int oldw, int oldh) { super.onSizeChanged(w, h, oldw, oldh); init(); } private RectF calculateBitmapBound() { int availableWidth = getWidth() - getPaddingLeft() - getPaddingRight(); int availableHeight = getHeight() - getPaddingTop() - getPaddingBottom(); int sideLength = Math.min(availableWidth, availableHeight); // 可用的直径 mRadius = sideLength / 2; int left = getPaddingLeft() + (availableWidth - sideLength) / 2; int top = getPaddingTop() + (availableHeight - sideLength) / 2; Log.d(TAG, "calculateBitmapBound: left >>> " + left + " top >>> " + top + " right >>> " + (left + sideLength) + " right >>> " + top + " bottom >>> " + (top + sideLength)); return new RectF(left, top, left + sideLength, top + sideLength); } private Bitmap getBitmapFromDrawable() { Drawable drawable = getDrawable(); if (drawable instanceof BitmapDrawable) { mBitmap = ((BitmapDrawable) drawable).getBitmap(); mBitmapWidth = mBitmap.getWidth(); mBitmapHeight = mBitmap.getHeight(); return mBitmap; } return null; } @Override protected void onDraw(Canvas canvas) { if (mBitmap == null) { super.onDraw(canvas); } Log.d(TAG, "onDraw: centerX >>> " + mBitmapBound.centerX() + " centerY >>> " + mBitmapBound.centerY()); canvas.drawCircle(mBitmapBound.centerX(), mBitmapBound.centerY(), mRadius, mFillPaint); // 绘制边框 canvas.drawCircle(mBorderBound.centerX(), mBorderBound.centerY(), mRadius, mBoundPaint); } private void updateShaderMatrix() { float scale; float dx = 0; float dy = 0; mShaderMatrix.set(null); // 调整缩放,使图片居中 if (mBitmapWidth * mBitmapBound.height() > mBitmapBound.width() * mBitmapHeight) { scale = mBitmapBound.height() / (float) mBitmapHeight; dx = (mBitmapBound.width() - mBitmapWidth * scale) * 0.5f; } else { scale = mBitmapBound.width() / (float) mBitmapWidth; dy = (mBitmapBound.height() - mBitmapHeight * scale) * 0.5f; } Log.d(TAG, "updateShaderMatrix: scale >>> " + scale); mShaderMatrix.setScale(scale, scale); // TODO: 16-10-15 http://chroya.iteye.com/blog/713869 // 回到中心点,便于下次缩放 mShaderMatrix.postTranslate((int) (dx + 0.5f) + mBitmapBound.left, (int) (dy + 0.5f) + mBitmapBound.top); mShader.setLocalMatrix(mShaderMatrix); }}以上就是Android中怎么通过自定义View实现圆形切图效果，小编相信有部分知识点可能是我们日常工作会见到或用到的。希望你能通过这篇文章学到更多知识。更多详情敬请关注编程网行业资讯频道。
