前言

在日常开发中，圆形的图片效果还是很常见的。可以通过给Paint设置Xfermode来实现，这里简单记录如下。

实现

实现圆形效果的核心是PorterDuffXfermode,对于PorterDuffXfermode,这里不展开，可以查询相关资料。

核心代码

//绘制背景
canvas.drawCircle(mSize / 2, mSize / 2, mSize / 2, 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);

自定义属性

<?xml version="1.0" encoding="utf-8"?><resources> <declare-styleable name="CircleView"> <!--定义资源--> <attr name="src" format="reference" /> <!--定义类型--> <attr name="type" format="enum"> <!--圆形--> <enum name="round" value="1" /> <!--矩形--> <enum name="rect" value="2" /> </attr> </declare-styleable></resources>

自定义控件

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); //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 ? 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; }}

注意：如果没有圆形的效果，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="@drawable/image" /> <com.wangyz.custom.CircleView android:layout_width="100dp" android:layout_height="100dp" android:layout_margin="10dp" app:src="@drawable/image" /> <com.wangyz.custom.CircleView android:layout_width="100dp" android:layout_height="100dp" android:layout_margin="10dp" app:src="@drawable/image" app:type="rect" /></LinearLayout>

效果

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。