自定义Drawable 实现图片圆角、圆形、椭圆形

什么是Drawable ?
Android 把所有显示出来的图形都抽象为drawable ，意思就是可绘制的，包括，图片、色块、背景等。
简单的drawable都是静态的图形，当然也有其他的，比如StateListDrawable，可以根据不同的触摸来变换不同的图形。也是通常我们在drawable文件中创建的selector.xml
我们通过简单三个例子来了解一下自定义drawable

效果图

图片圆形的实现

/**
 * 圆形图片实现
 */

public class CircleDrawable extends BitmapDrawable {

    private final Paint mPaint;

    public CircleDrawable(Resources resources, Bitmap bitmap){
        super(resources,bitmap);
        BitmapShader shader=new BitmapShader(bitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setShader(shader);
        mPaint.setColor(Color.RED);
    }

    @Override
    public void draw(Canvas canvas) {
        int width = getBitmap().getWidth();
        int height = getBitmap().getHeight();
        int radius = Math.min(width/2, height/2);
        int x = (width>radius+radius)?width/2:radius;
        int y = (height>radius+radius)?height/2:radius;
        canvas.drawCircle(x,y,radius,mPaint);
    }

    /**
     * 这两个方法可以获取到drawable绘制的区域，不过ImageView的源码中调用的是下面的
     * @param bounds
     */
    @Override
    public void setBounds(Rect bounds) {
        super.setBounds(bounds);
    }

    /**
     * 这两个方法可以获取到drawable绘制的区域 Imagview中会调用该方法，设置宽高
     */
    @Override
    public void setBounds(int left, int top, int right, int bottom) {
        super.setBounds(left, top, right, bottom);
    }
}

图片圆角的实现

/**
 * 圆角图片实现
 */

public class RoundDrawable extends BitmapDrawable {


    private final Paint paint;
    private float radisu;
    private RectF rectF;

    public RoundDrawable(Resources resources, Bitmap bitmap){
        super(resources,bitmap);
        BitmapShader shader=new BitmapShader(bitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);
        paint = new Paint();
        paint.setAntiAlias(true);
        paint.setShader(shader);
    }

    @Override
    public void draw(Canvas canvas) {
        canvas.drawRoundRect(rectF,radisu,radisu,paint);
    }

    public void setRadius(float radisu){

        this.radisu = radisu;
    }


    @Override
    public void setBounds(int left, int top, int right, int bottom) {
        rectF = new RectF(left,top,right,bottom);
    }
}

椭圆图片的实现

/**
 * 椭圆图片实现
 */

public class OvalDrawable extends BitmapDrawable {

    private final Paint mPaint;
    private RectF rectF;

    public OvalDrawable(Resources res, Bitmap bitmap){
        super(res,bitmap);
        BitmapShader shader=new BitmapShader(bitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setDither(true);
        mPaint.setShader(shader);
    }

    @Override
    public void draw(Canvas canvas) {
        canvas.drawOval(rectF,mPaint);
    }

    @Override
    public void setBounds(int left, int top, int right, int bottom) {
        super.setBounds(left, top, right, bottom);
        rectF = new RectF(left,top,right,bottom);
    }
}

按钮点击调用

public void onClick(View v) {
        switch (v.getId()) {
            case R.id.original: // 原图
                imageView.setImageResource(R.drawable.demo);
                break;

            case R.id.circle: // 圆形
                Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.demo);
                CircleDrawable drawable = new CircleDrawable(getResources(), bitmap);
                imageView.setImageDrawable(drawable);
                break;

            case R.id.round: // 圆角
                Bitmap roundBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.demo);
                RoundDrawable roundDrawable = new RoundDrawable(getResources(), roundBitmap);
                roundDrawable.setRadius(30);
                imageView.setImageDrawable(roundDrawable);
                break;

            case R.id.oval: // 椭圆
                Bitmap ovalBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.demo);
                OvalDrawable ovalDrawable = new OvalDrawable(getResources(), ovalBitmap);
                imageView.setImageDrawable(ovalDrawable);
                break;

        }
    }

MainActivity界面xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com.lg.customdrawable.MainActivity">

    <ImageView
        android:id="@+id/image_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="5dp"
        android:layout_marginRight="5dp"
        android:src="@drawable/demo" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <Button
            android:id="@+id/original"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="原图" />

        <Button
            android:id="@+id/circle"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="圆形" />

        <Button
            android:id="@+id/round"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="圆角" />

        <Button
            android:id="@+id/oval"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="椭圆" />
    </LinearLayout>
</LinearLayout>

总结
简单实现了三种效果，帮助理解自定义Drawable。
Demo下载地址有需要的可以看下