Android 设置投影效果

1. elevation设置投影

android api（限制 21 以上 ）,不过我们还是无法自定义投影颜色，透明度,大小等

2. UI制作.9图片

3. paint.setShadowLayer(float radius, float dx, float dy, int shadowColor);

这个方法可以达到这样一个效果，在使用canvas画图时给视图顺带上一层阴影效果。
简单介绍一下这几个参数：

• radius: 阴影半径，主要可以控制阴影的模糊效果以及阴影扩散出去的大小。
• dx：阴影在X轴方向上的偏移量
• dy: 阴影在Y轴方向上的偏移量
• shadowColor: 阴影颜色

思路:

1. 通过在父布局中绘制整个阴影背景，子布局为所要显示的View
2. 给控件设置背景，在背景上做投影效果

3.1 自定义ShadowLayout

public class ShadowLayout extends FrameLayout {
     
    public static final String TAG = "ShadowLayout";

    // 阴影颜色
    private int mShadowColor;
    // 阴影范围大小
    private float mShadowRadius;
    // 阴影圆角光滑度
    private float mCornerRadius;
    // 阴影x轴偏移量
    private float mDx;
    // 阴影y轴偏移量
    private float mDy;

    private boolean mInvalidateShadowOnSizeChanged = true;
    private boolean mForceInvalidateShadow = false;

    public ShadowLayout(Context context) {
     
        super(context);
        initView(context, null);
    }

    public ShadowLayout(Context context, AttributeSet attrs) {
     
        super(context, attrs);
        initView(context, attrs);
    }

    public ShadowLayout(Context context, AttributeSet attrs, int defStyleAttr) {
     
        super(context, attrs, defStyleAttr);
        initView(context, attrs);
    }

    @Override
    protected int getSuggestedMinimumWidth() {
     
        return 0;
    }

    @Override
    protected int getSuggestedMinimumHeight() {
     
        return 0;
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
     
        super.onSizeChanged(w, h, oldw, oldh);
        if (w > 0 && h > 0 && (getBackground() == null || mInvalidateShadowOnSizeChanged || mForceInvalidateShadow)) {
     
            mForceInvalidateShadow = false;
            setBackgroundCompat(w, h);
        }
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
     
        super.onLayout(changed, left, top, right, bottom);
        if (mForceInvalidateShadow) {
     
            mForceInvalidateShadow = false;
            setBackgroundCompat(right - left, bottom - top);
        }
    }

    public void setInvalidateShadowOnSizeChanged(boolean invalidateShadowOnSizeChanged) {
     
        mInvalidateShadowOnSizeChanged = invalidateShadowOnSizeChanged;
    }

    public void invalidateShadow() {
     
        mForceInvalidateShadow = true;
        requestLayout();
        invalidate();
    }

    private void initView(Context context, AttributeSet attrs) {
     
        initAttributes(context, attrs);
        /** x偏离量 **/
        int xPadding = (int) (mShadowRadius + Math.abs(mDx));
        /** y偏离量 **/
        int yPadding = (int) (mShadowRadius + Math.abs(mDy));
        setPadding(xPadding, yPadding, xPadding, yPadding);
    }

    private void initAttributes(Context context, AttributeSet attrs) {
     
        TypedArray attr = getTypedArray(context, attrs, R.styleable.ShadowLayout);
        if (attr == null) {
     
            return;
        }

        try {
     
            mCornerRadius = attr.getDimension(R.styleable.ShadowLayout_sl_cornerRadius, 0);
            mShadowRadius = attr.getDimension(R.styleable.ShadowLayout_sl_shadowRadius, 10);
            mDx = attr.getDimension(R.styleable.ShadowLayout_sl_dx, 0);
            mDy = attr.getDimension(R.styleable.ShadowLayout_sl_dy, 0);
            mShadowColor = attr.getColor(R.styleable.ShadowLayout_sl_shadowColor, Color.parseColor("#88757575"));
        } finally {
     
            attr.recycle();
        }
    }

    @SuppressWarnings("deprecation")
    private void setBackgroundCompat(int w, int h) {
     
        Log.i(TAG, "setBackgroundCompat: w=" + w + ", h=" + h);
        Bitmap bitmap = createShadowBitmap(w, h, mCornerRadius, mShadowRadius, mDx, mDy, mShadowColor, Color.TRANSPARENT);
        BitmapDrawable drawable = new BitmapDrawable(getResources(), bitmap);
        if (Build.VERSION.SDK_INT <= Build.VERSION_CODES.JELLY_BEAN) {
     
            setBackgroundDrawable(drawable);
        } else {
     
            setBackground(drawable);
        }
    }


    private TypedArray getTypedArray(Context context, AttributeSet attributeSet, int[] attr) {
     
        return context.obtainStyledAttributes(attributeSet, attr, 0, 0);
    }

    private Bitmap createShadowBitmap(int shadowWidth, int shadowHeight, float cornerRadius, float shadowRadius,
                                      float dx, float dy, int shadowColor, int fillColor) {
     

        Bitmap output = Bitmap.createBitmap(shadowWidth, shadowHeight, Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(output);

        RectF shadowRect = new RectF(
                shadowRadius,
                shadowRadius,
                shadowWidth - shadowRadius,
                shadowHeight - shadowRadius);

        if (dy > 0) {
     
            shadowRect.top += dy;
            shadowRect.bottom -= dy;
        } else if (dy < 0) {
     
            shadowRect.top += Math.abs(dy);
            shadowRect.bottom -= Math.abs(dy);
        }

        if (dx > 0) {
     
            shadowRect.left += dx;
            shadowRect.right -= dx;
        } else if (dx < 0) {
     
            shadowRect.left += Math.abs(dx);
            shadowRect.right -= Math.abs(dx);
        }

        Paint shadowPaint = new Paint();
        shadowPaint.setAntiAlias(true);
        shadowPaint.setColor(fillColor);
        shadowPaint.setStyle(Paint.Style.FILL);

        if (!isInEditMode()) {
     
            // 阴影的区域默认在绘制区域，阴影移动均相对于绘制区域
            shadowPaint.setShadowLayer(shadowRadius, dx, dy, shadowColor);
        }

        canvas.drawRoundRect(shadowRect, cornerRadius, cornerRadius, shadowPaint);
        return output;
    }

}

attrs.xml

<declare-styleable name="ShadowLayout">
   	<attr name="sl_cornerRadius" format="dimension" />
    <attr name="sl_shadowRadius" format="dimension" />
    <attr name="sl_shadowColor" format="color" />
    <attr name="sl_dx" format="dimension" />
    <attr name="sl_dy" format="dimension" />
declare-styleable>

例如要给TextView添加投影效果，使用如下

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/ll_content"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <com.base.module.customviewexer.ShadowLayout
        android:layout_width="200dp"
        android:layout_height="100dp"
        android:layout_centerInParent="true"
        app:sl_dy="5dp">

        <TextView
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="#ffffff"
            android:gravity="center"
            android:text="hello world!" />
    </com.base.module.customviewexer.ShadowLayout>
</RelativeLayout>

显示效果

3.2 自定义背景ShadowDrawable

public class ShadowDrawable extends Drawable {
     

    private Paint mShadowPaint;
    private Paint mBgPaint;
    private int mShadowRadius;
    private int mShape;
    private int mShapeRadius;
    private int mOffsetX;
    private int mOffsetY;
    private int mBgColor[];
    private RectF mRect;

    public final static int SHAPE_ROUND = 1;
    public final static int SHAPE_CIRCLE = 2;

    private ShadowDrawable(int shape, int[] bgColor, int shapeRadius, int shadowColor, int shadowRadius, int offsetX, int offsetY) {
     
        this.mShape = shape;
        this.mBgColor = bgColor;
        this.mShapeRadius = shapeRadius;
        this.mShadowRadius = shadowRadius;
        this.mOffsetX = offsetX;
        this.mOffsetY = offsetY;

        mShadowPaint = new Paint();
        mShadowPaint.setColor(Color.TRANSPARENT);
        mShadowPaint.setAntiAlias(true);
        mShadowPaint.setShadowLayer(shadowRadius, offsetX, offsetY, shadowColor);
        mShadowPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_ATOP));

        mBgPaint = new Paint();
        mBgPaint.setAntiAlias(true);
    }

    @Override
    public void setBounds(int left, int top, int right, int bottom) {
     
        super.setBounds(left, top, right, bottom);
        mRect = new RectF(left + mShadowRadius - mOffsetX, top + mShadowRadius - mOffsetY, right - mShadowRadius - mOffsetX,
                bottom - mShadowRadius - mOffsetY);
    }

    @Override
    public void draw(@NonNull Canvas canvas) {
     
        if (mBgColor != null) {
     
            if (mBgColor.length == 1) {
     
                mBgPaint.setColor(mBgColor[0]);
            } else {
     
                mBgPaint.setShader(new LinearGradient(mRect.left, mRect.height() / 2, mRect.right,
                        mRect.height() / 2, mBgColor, null, Shader.TileMode.CLAMP));
            }
        }

        if (mShape == SHAPE_ROUND) {
     
            canvas.drawRoundRect(mRect, mShapeRadius, mShapeRadius, mShadowPaint);
            canvas.drawRoundRect(mRect, mShapeRadius, mShapeRadius, mBgPaint);
        } else {
     
            canvas.drawCircle(mRect.centerX(), mRect.centerY(), Math.min(mRect.width(), mRect.height()) / 2, mShadowPaint);
            canvas.drawCircle(mRect.centerX(), mRect.centerY(), Math.min(mRect.width(), mRect.height()) / 2, mBgPaint);
        }
    }

    @Override
    public void setAlpha(int alpha) {
     
        mShadowPaint.setAlpha(alpha);
    }

    @Override
    public void setColorFilter(@Nullable ColorFilter colorFilter) {
     
        mShadowPaint.setColorFilter(colorFilter);
    }

    @Override
    public int getOpacity() {
     
        return PixelFormat.TRANSLUCENT;
    }


    public static void setShadowDrawable(View view, int shapeRadius, int shadowColor, int shadowRadius, int offsetX, int offsetY) {
     
        ShadowDrawable drawable = new ShadowDrawable.Builder()
                .setShapeRadius(shapeRadius)
                .setShadowColor(shadowColor)
                .setShadowRadius(shadowRadius)
                .setOffsetX(offsetX)
                .setOffsetY(offsetY)
                .builder();
        view.setLayerType(View.LAYER_TYPE_SOFTWARE, null);
        ViewCompat.setBackground(view, drawable);
    }

    public static void setShadowDrawable(View view, int bgColor, int shapeRadius, int shadowColor, int shadowRadius, int offsetX, int offsetY) {
     
        ShadowDrawable drawable = new ShadowDrawable.Builder()
                .setBgColor(bgColor)
                .setShapeRadius(shapeRadius)
                .setShadowColor(shadowColor)
                .setShadowRadius(shadowRadius)
                .setOffsetX(offsetX)
                .setOffsetY(offsetY)
                .builder();
        view.setLayerType(View.LAYER_TYPE_SOFTWARE, null);
        ViewCompat.setBackground(view, drawable);
    }

    public static void setShadowDrawable(View view, int shape, int bgColor, int shapeRadius, int shadowColor, int shadowRadius, int offsetX, int offsetY) {
     
        ShadowDrawable drawable = new ShadowDrawable.Builder()
                .setShape(shape)
                .setBgColor(bgColor)
                .setShapeRadius(shapeRadius)
                .setShadowColor(shadowColor)
                .setShadowRadius(shadowRadius)
                .setOffsetX(offsetX)
                .setOffsetY(offsetY)
                .builder();
        view.setLayerType(View.LAYER_TYPE_SOFTWARE, null);
        ViewCompat.setBackground(view, drawable);
    }

    public static void setShadowDrawable(View view, int[] bgColor, int shapeRadius, int shadowColor, int shadowRadius, int offsetX, int offsetY) {
     
        ShadowDrawable drawable = new ShadowDrawable.Builder()
                .setBgColor(bgColor)
                .setShapeRadius(shapeRadius)
                .setShadowColor(shadowColor)
                .setShadowRadius(shadowRadius)
                .setOffsetX(offsetX)
                .setOffsetY(offsetY)
                .builder();
        view.setLayerType(View.LAYER_TYPE_SOFTWARE, null);
        ViewCompat.setBackground(view, drawable);
    }

    public static class Builder {
     
        private int mShape;
        private int mShapeRadius;
        private int mShadowColor;
        private int mShadowRadius;
        private int mOffsetX = 0;
        private int mOffsetY = 0;
        private int[] mBgColor;

        public Builder() {
     
            mShape = ShadowDrawable.SHAPE_ROUND;
            mShapeRadius = 12;
            mShadowColor = Color.parseColor("#4d000000");
            mShadowRadius = 18;
            mOffsetX = 0;
            mOffsetY = 0;
            mBgColor = new int[1];
            mBgColor[0] = Color.TRANSPARENT;
        }

        public Builder setShape(int mShape) {
     
            this.mShape = mShape;
            return this;
        }

        public Builder setShapeRadius(int ShapeRadius) {
     
            this.mShapeRadius = ShapeRadius;
            return this;
        }

        public Builder setShadowColor(int shadowColor) {
     
            this.mShadowColor = shadowColor;
            return this;
        }

        public Builder setShadowRadius(int shadowRadius) {
     
            this.mShadowRadius = shadowRadius;
            return this;
        }

        public Builder setOffsetX(int OffsetX) {
     
            this.mOffsetX = OffsetX;
            return this;
        }

        public Builder setOffsetY(int OffsetY) {
     
            this.mOffsetY = OffsetY;
            return this;
        }

        public Builder setBgColor(int BgColor) {
     
            this.mBgColor[0] = BgColor;
            return this;
        }

        public Builder setBgColor(int[] BgColor) {
     
            this.mBgColor = BgColor;
            return this;
        }

        public ShadowDrawable builder() {
     
            return new ShadowDrawable(mShape, mBgColor, mShapeRadius, mShadowColor, mShadowRadius, mOffsetX, mOffsetY);
        }
    }
}

布局文件

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/ll_content"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:id="@+id/tv_text"
        android:layout_width="200dp"
        android:layout_height="100dp"
        android:layout_centerInParent="true"
        android:background="#ffffff"
        android:gravity="center"
        android:text="hello world!" />
RelativeLayout>

Activity中使用

public class MainActivity extends AppCompatActivity {
     
    private TextView mTvText;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
     
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mTvText = findViewById(R.id.tv_text);
        /* 
        1. 需要设置的view
        2. 背景主题颜色
        3. 背景弧度半径
        4. shadow的颜色
        5. shadow的扩散半径大小
        6. shadow的x轴偏移
        7. shadow的y周偏移
		*/
        ShadowDrawable.setShadowDrawable(mTvText, Color.parseColor("#ffffff"), 10, Color.parseColor("#25000000"), 10, 0, 10);
    }
}

实现效果

这种目前的限制是正常背景只能纯色，无法设置图片，选择器等，不过理解了原理，如果有需要也可以进行定制。