前言

在日常開發中，圓形的圖片效果還是很常見的。可以通過給Paint設置Xfermode來實現，這里簡單記錄如下。

實現

實現圓形效果的核心是PorterDuffXfermode,對于PorterDuffXfermode,這里不展開，可以查詢相關資料。

核心代碼

//繪制背景canvas.drawCircle(mSize / 2, mSize / 2, mSize / 2, mPaint);//設置模式為:顯示背景層和上層的交集，且顯示上層圖像mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));//繪制要顯示的圖像canvas.drawBitmap(mSrcBitmap, 0, 0, mPaint);//重置XfermodemPaint.setXfermode(null);

自定義屬性

<?xml version='1.0' encoding='utf-8'?><resources> <declare-styleable name='CircleView'> <!--定義資源--> <attr name='src' format='reference' /> <!--定義類型--> <attr name='type' format='enum'> <!--圓形--> <enum name='round' value='1' /> <!--矩形--> <enum name='rect' value='2' /> </attr> </declare-styleable></resources>

自定義控件

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); //繪制背景 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); } //設置模式為:顯示背景層和上層的交集，且顯示上層圖像 mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN)); //繪制要顯示的圖像 canvas.drawBitmap(mSrcBitmap, 0, 0, mPaint); //重置Xfermode mPaint.setXfermode(null); } private void init() { //禁用硬件加速,否則可能無法繪制圓形 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 ? size : DEFAULT_SIZE; } /** * 獲取縮放后的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); } /** * 計算縮放比例 * * @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; }}

注意：如果沒有圓形的效果，那么可能需要禁用硬件加速：setLayerType(LAYER_TYPE_HARDWARE, null)

布局

<?xml version='1.0' encoding='utf-8'?><LinearLayout xmlns:android='http://schemas.android.com/apk/res/android' xmlns:app='http://schemas.android.com/apk/res-auto' xmlns:tools='http://schemas.android.com/tools' android:layout_width='match_parent' android:layout_height='match_parent' android:gravity='center_horizontal' android:orientation='vertical' tools:context='.MainActivity'> <com.wangyz.custom.CircleView android:layout_width='wrap_content' android:layout_height='wrap_content' android:layout_margin='10dp' app:src='http://m.4tl426be.cn/bcjs/@drawable/image' /> <com.wangyz.custom.CircleView android:layout_width='100dp' android:layout_height='100dp' android:layout_margin='10dp' app:src='http://m.4tl426be.cn/bcjs/@drawable/image' /> <com.wangyz.custom.CircleView android:layout_width='100dp' android:layout_height='100dp' android:layout_margin='10dp' app:src='http://m.4tl426be.cn/bcjs/@drawable/image' app:type='rect' /></LinearLayout>

效果

以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持好吧啦網。