Main categories:

package de.hdodenhof.circleimageview;
import edu.njupt.zhb.main.R;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Bitmap;
import android.graphics.BitmapShader;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.RectF;
import android.graphics.Shader;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.ColorDrawable;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.widget.ImageView;

public class CircleImageView extends ImageView {

private static final ScaleType SCALE_TYPE = ScaleType.CENTER_CROP;

private static final Bitmap.Config BITMAP_CONFIG = Bitmap.Config.ARGB_8888;
private static final int COLORDRAWABLE_DIMENSION = 1;

private static final int DEFAULT_BORDER_WIDTH = 0;
private static final int DEFAULT_BORDER_COLOR = Color.BLACK;

private final RectF mDrawableRect = new RectF();
private final RectF mBorderRect = new RectF();

private final Matrix mShaderMatrix = new Matrix();
private final Paint mBitmapPaint = new Paint();
private final Paint mBorderPaint = new Paint();

private int mBorderColor = DEFAULT_BORDER_COLOR;
private int mBorderWidth = DEFAULT_BORDER_WIDTH;

private Bitmap mBitmap;
private BitmapShader mBitmapShader;
private int mBitmapWidth;
private int mBitmapHeight;

private float mDrawableRadius;
private float mBorderRadius;

private boolean mReady;
private boolean mSetupPending;

public CircleImageView(Context context) {
    super(context);
}

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

public CircleImageView(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
    super.setScaleType(SCALE_TYPE);

    TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.CircleImageView, defStyle, 0);

    mBorderWidth = a.getDimensionPixelSize(R.styleable.CircleImageView_border_width, DEFAULT_BORDER_WIDTH);
    mBorderColor = a.getColor(R.styleable.CircleImageView_border_color, DEFAULT_BORDER_COLOR);

    a.recycle();

    mReady = true;

    if (mSetupPending) {
        setup();
        mSetupPending = false;
    }
}

@Override
public ScaleType getScaleType() {
    return SCALE_TYPE;
}

@Override
public void setScaleType(ScaleType scaleType) {
    if (scaleType != SCALE_TYPE) {
        throw new IllegalArgumentException(String.format("ScaleType %s not supported.", scaleType));
    }
}

@Override
protected void onDraw(Canvas canvas) {
    if (getDrawable() == null) {
        return;
    }

    canvas.drawCircle(getWidth() / 2, getHeight() / 2, mDrawableRadius, mBitmapPaint);
    canvas.drawCircle(getWidth() / 2, getHeight() / 2, mBorderRadius, mBorderPaint);
}

@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
    super.onSizeChanged(w, h, oldw, oldh);
    setup();
}

public int getBorderColor() {
    return mBorderColor;
}

public void setBorderColor(int borderColor) {
    if (borderColor == mBorderColor) {
        return;
    }

    mBorderColor = borderColor;
    mBorderPaint.setColor(mBorderColor);
    invalidate();
}

public int getBorderWidth() {
    return mBorderWidth;
}

public void setBorderWidth(int borderWidth) {
    if (borderWidth == mBorderWidth) {
        return;
    }

    mBorderWidth = borderWidth;
    setup();
}

@Override
public void setImageBitmap(Bitmap bm) {
    super.setImageBitmap(bm);
    mBitmap = bm;
    setup();
}

@Override
public void setImageDrawable(Drawable drawable) {
    super.setImageDrawable(drawable);
    mBitmap = getBitmapFromDrawable(drawable);
    setup();
}

@Override
public void setImageResource(int resId) {
    super.setImageResource(resId);
    mBitmap = getBitmapFromDrawable(getDrawable());
    setup();
}

private Bitmap getBitmapFromDrawable(Drawable drawable) {
    if (drawable == null) {
        return null;
    }

    if (drawable instanceof BitmapDrawable) {
        return ((BitmapDrawable) drawable).getBitmap();
    }

    try {
        Bitmap bitmap;

        if (drawable instanceof ColorDrawable) {
            bitmap = Bitmap.createBitmap(COLORDRAWABLE_DIMENSION, COLORDRAWABLE_DIMENSION, BITMAP_CONFIG);
        } else {
            bitmap = Bitmap.createBitmap(drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight(), BITMAP_CONFIG);
        }

        Canvas canvas = new Canvas(bitmap);
        drawable.setBounds(0, 0, canvas.getWidth(), canvas.getHeight());
        drawable.draw(canvas);
        return bitmap;
    } catch (OutOfMemoryError e) {
        return null;
    }
}

private void setup() {
    if (!mReady) {
        mSetupPending = true;
        return;
    }

    if (mBitmap == null) {
        return;
    }

    mBitmapShader = new BitmapShader(mBitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);

    mBitmapPaint.setAntiAlias(true);
    mBitmapPaint.setShader(mBitmapShader);

    mBorderPaint.setStyle(Paint.Style.STROKE);
    mBorderPaint.setAntiAlias(true);
    mBorderPaint.setColor(mBorderColor);
    mBorderPaint.setStrokeWidth(mBorderWidth);

    mBitmapHeight = mBitmap.getHeight();
    mBitmapWidth = mBitmap.getWidth();

    mBorderRect.set(0, 0, getWidth(), getHeight());
    mBorderRadius = Math.min((mBorderRect.height() - mBorderWidth) / 2, (mBorderRect.width() - mBorderWidth) / 2);

    mDrawableRect.set(mBorderWidth, mBorderWidth, mBorderRect.width() - mBorderWidth, mBorderRect.height() - mBorderWidth);
    mDrawableRadius = Math.min(mDrawableRect.height() / 2, mDrawableRect.width() / 2);

    updateShaderMatrix();
    invalidate();
}

private void updateShaderMatrix() {
    float scale;
    float dx = 0;
    float dy = 0;

    mShaderMatrix.set(null);

    if (mBitmapWidth * mDrawableRect.height() > mDrawableRect.width() * mBitmapHeight) {
        scale = mDrawableRect.height() / (float) mBitmapHeight;
        dx = (mDrawableRect.width() - mBitmapWidth * scale) * 0.5f;
    } else {
        scale = mDrawableRect.width() / (float) mBitmapWidth;
        dy = (mDrawableRect.height() - mBitmapHeight * scale) * 0.5f;
    }

    mShaderMatrix.setScale(scale, scale);
    mShaderMatrix.postTranslate((int) (dx + 0.5f) + mBorderWidth, (int) (dy + 0.5f) + mBorderWidth);

    mBitmapShader.setLocalMatrix(mShaderMatrix);
}

}

Customized attributes: res/values/attrs.xml

<?xml version="1.0" encoding="utf-8"?>

Layout files used:

<?xml version="1.0" encoding="utf-8"?>

    <de.hdodenhof.circleimageview.CircleImageView
        android:layout_width="160dp"
        android:layout_height="160dp"
        android:layout_centerInParent="true"
        android:src="@drawable/demo"
        app:border_width="2dp"
        app:border_color="@color/dark" />

</RelativeLayout>

<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_weight="1"
    android:padding="@dimen/base_padding"
    android:background="@color/dark">

    <de.hdodenhof.circleimageview.CircleImageView
        android:layout_width="160dp"
        android:layout_height="160dp"
        android:layout_centerInParent="true"
        android:src="@drawable/lena"
        app:border_width="2dp"
        app:border_color="@color/light" />

</RelativeLayout>

Effect:

Note: Some developers may also find that if we need a circular image Button, we don't have to write it ourselves. If the icon of ImageButton is fixed, we can let the designer design a circular image for me, and then set it directly on ImageButton. Note, however, that our circular ImageView is a custom control, that is, no matter what image you set up, it shows a circular image. For example, the user's avatar settings in E-mail, no matter what photos the user takes, show a circle.