1.新建一个RoundImageView.java文件

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package com.jhg.freshman;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Bitmap;
import android.graphics.BitmapShader;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.RectF;
import android.graphics.Shader;
import android.graphics.drawable.Drawable;
import android.os.Build;
import android.util.AttributeSet;
import android.util.TypedValue;
import android.widget.ImageView;
    public class RoundImageView extends android.support.v7.widget.AppCompatImageView {
        /**
         * 圆形模式
         */
        private static final int MODE_CIRCLE = 1;
        /**
         * 普通模式
         */
        private static final int MODE_NONE = 0;
        /**
         * 圆角模式
         */
        private static final int MODE_ROUND = 2;
        private Paint mPaint;
        private int currMode = 0;
        /**
         * 圆角半径
         */
        private int currRound = dp2px(10);

        public RoundImageView(Context context) {
            super(context);
            initViews();
        }

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

        public RoundImageView(Context context, AttributeSet attrs, int defStyleAttr) {
            super(context, attrs, defStyleAttr);
            obtainStyledAttrs(context, attrs, defStyleAttr);
            initViews();
        }

        private void obtainStyledAttrs(Context context, AttributeSet attrs, int defStyleAttr) {
            TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.RoundImageView, defStyleAttr, 0);
            currMode = a.hasValue(R.styleable.RoundImageView_type) ? a.getInt(R.styleable.RoundImageView_type, MODE_NONE) : MODE_NONE;
            currRound = a.hasValue(R.styleable.RoundImageView_radius) ? a.getDimensionPixelSize(R.styleable.RoundImageView_radius, currRound) : currRound;
            a.recycle();
        }

        private void initViews() {
            mPaint = new Paint(Paint.ANTI_ALIAS_FLAG | Paint.DITHER_FLAG);
        }

        @Override
        protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
            /**
             * 当模式为圆形模式的时候，我们强制让宽高一致
             */
            if (currMode == MODE_CIRCLE) {
                super.onMeasure(widthMeasureSpec, heightMeasureSpec);
                int result = Math.min(getMeasuredHeight(), getMeasuredWidth());
                setMeasuredDimension(result, result);
            } else {
                super.onMeasure(widthMeasureSpec, heightMeasureSpec);
            }
        }

        @Override
        protected void onDraw(Canvas canvas) {
            Drawable mDrawable = getDrawable();
            Matrix mDrawMatrix = getImageMatrix();
            if (mDrawable == null) {
                return; // couldn't resolve the URI
            }

            if (mDrawable.getIntrinsicWidth() == 0 || mDrawable.getIntrinsicHeight() == 0) {
                return;     // nothing to draw (empty bounds)
            }

            if (mDrawMatrix == null && getPaddingTop() == 0 && getPaddingLeft() == 0) {
                mDrawable.draw(canvas);
            } else {
                final int saveCount = canvas.getSaveCount();
                canvas.save();

                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
                    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 (currMode == MODE_CIRCLE) {//当为圆形模式的时候
                    Bitmap bitmap = drawable2Bitmap(mDrawable);
                    mPaint.setShader(new BitmapShader(bitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP));
                    canvas.drawCircle(getWidth() / 2, getHeight() / 2, getWidth() / 2, mPaint);
                } else if (currMode == MODE_ROUND) {//当为圆角模式的时候
                    Bitmap bitmap = drawable2Bitmap(mDrawable);
                    mPaint.setShader(new BitmapShader(bitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP));
                    canvas.drawRoundRect(new RectF(getPaddingLeft(), getPaddingTop(), getWidth() - getPaddingRight(), getHeight() - getPaddingBottom()),
                            currRound, currRound, mPaint);
                } else {
                    if (mDrawMatrix != null) {
                        canvas.concat(mDrawMatrix);
                    }
                    mDrawable.draw(canvas);
                }
                canvas.restoreToCount(saveCount);
            }
        }

        /**
         * drawable转换成bitmap
         */
        private Bitmap drawable2Bitmap(Drawable drawable) {
            if (drawable == null) {
                return null;
            }
            Bitmap bitmap = Bitmap.createBitmap(getWidth(), getHeight(), Bitmap.Config.ARGB_8888);
            Canvas canvas = new Canvas(bitmap);
            //根据传递的scaletype获取matrix对象，设置给bitmap
            Matrix matrix = getImageMatrix();
            if (matrix != null) {
                canvas.concat(matrix);
            }
            drawable.draw(canvas);
            return bitmap;
        }

        private int dp2px(float value) {
            return (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, value, getResources().getDisplayMetrics());
        }
    }

2.在Value下新建一个attrs.xml文件

    
        
            
            
        
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3.在layout布局文件中使用RoundImage控件

文章题目：Androidstudio实现圆形ImageView的方法步骤
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