RelativeLayout with backward-compatible foreground support.

attrs.xml

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

<!--
  ~ Copyright (c) 2015 Zhang Hai
  ~
  ~ Licensed under the Apache License, Version 2.0 (the "License");
  ~ you may not use this file except in compliance with the License.
  ~ You may obtain a copy of the License at
  ~
  ~      http://www.apache.org/licenses/LICENSE-2.0
  ~
  ~ Unless required by applicable law or agreed to in writing, software
  ~ distributed under the License is distributed on an "AS IS" BASIS,
  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  ~ See the License for the specific language governing permissions and
  ~ limitations under the License.
  -->

<resources>

    <declare-styleable name="ForegroundRelativeLayout">
        <attr name="android:foreground" />
        <attr name="android:foregroundGravity" />
        <attr name="android:foregroundInsidePadding" />
    </declare-styleable>
</resources>

ForegroundRelativeLayout.java

/*
 * Copyright (c) 2015 Zhang Hai
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.yourapplication;

import android.annotation.TargetApi;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.os.Build;
import android.support.annotation.NonNull;
import android.support.v4.view.GravityCompat;
import android.support.v4.view.ViewCompat;
import android.util.AttributeSet;
import android.view.Gravity;
import android.widget.RelativeLayout;

import me.zhanghai.android.douya.R;

public class ForegroundRelativeLayout extends RelativeLayout {

    private boolean mHasNativeBackground;

    private Drawable mForeground;

    private final Rect mSelfBounds = new Rect();
    private final Rect mOverlayBounds = new Rect();
    private int mForegroundGravity = Gravity.FILL;
    private boolean mForegroundInPadding = true;

    private boolean mForegroundBoundsChanged = false;

    public ForegroundRelativeLayout(Context context) {
        super(context);

        init(context, null, 0, 0);
    }

    public ForegroundRelativeLayout(Context context, AttributeSet attrs) {
        super(context, attrs);

        init(context, attrs, 0, 0);
    }

    public ForegroundRelativeLayout(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);

        init(context, attrs, defStyleAttr, 0);
    }

    @TargetApi(Build.VERSION_CODES.LOLLIPOP)
    public ForegroundRelativeLayout(Context context, AttributeSet attrs, int defStyleAttr,
                                    int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);

        init(context, attrs, defStyleAttr, defStyleRes);
    }

    private void init(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {

        mHasNativeBackground = Build.VERSION.SDK_INT >= Build.VERSION_CODES.M
                && context.getApplicationInfo().targetSdkVersion >= Build.VERSION_CODES.M;

        if (mHasNativeBackground) {
            return;
        }

        TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.ForegroundRelativeLayout,
                defStyleAttr, defStyleRes);

        mForegroundGravity = a.getInt(
                R.styleable.ForegroundRelativeLayout_android_foregroundGravity, mForegroundGravity);

        Drawable foreground = a.getDrawable(
                R.styleable.ForegroundRelativeLayout_android_foreground);
        if (foreground != null) {
            setForeground(foreground);
        }

        mForegroundInPadding = a.getBoolean(
                R.styleable.ForegroundRelativeLayout_android_foregroundInsidePadding, true);

        a.recycle();
    }

    /**
     * {@inheritDoc}
     */
    public int getForegroundGravity() {

        if (mHasNativeBackground) {
            return super.getForegroundGravity();
        }

        return mForegroundGravity;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void setForegroundGravity(int foregroundGravity) {

        if (mHasNativeBackground) {
            super.setForegroundGravity(foregroundGravity);
            return;
        }

        if (mForegroundGravity != foregroundGravity) {

            if ((foregroundGravity & Gravity.RELATIVE_HORIZONTAL_GRAVITY_MASK) == 0) {
                foregroundGravity |= Gravity.START;
            }

            if ((foregroundGravity & Gravity.VERTICAL_GRAVITY_MASK) == 0) {
                foregroundGravity |= Gravity.TOP;
            }

            mForegroundGravity = foregroundGravity;

            requestLayout();
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void setVisibility(int visibility) {
        super.setVisibility(visibility);

        if (mHasNativeBackground) {
            return;
        }

        if (mForeground != null) {
            mForeground.setVisible(visibility == VISIBLE, false);
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected boolean verifyDrawable(Drawable who) {

        if (mHasNativeBackground) {
            return super.verifyDrawable(who);
        }

        return super.verifyDrawable(who) || (who == mForeground);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void jumpDrawablesToCurrentState() {
        super.jumpDrawablesToCurrentState();

        if (mHasNativeBackground) {
            return;
        }

        if (mForeground != null) {
            mForeground.jumpToCurrentState();
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected void drawableStateChanged() {
        super.drawableStateChanged();

        if (mHasNativeBackground) {
            return;
        }

        if (mForeground != null && mForeground.isStateful()) {
            mForeground.setState(getDrawableState());
        }
    }

    /**
     * {@inheritDoc}
     */
    @TargetApi(Build.VERSION_CODES.LOLLIPOP)
    @Override
    public void drawableHotspotChanged(float x, float y) {
        super.drawableHotspotChanged(x, y);

        if (mHasNativeBackground) {
            return;
        }

        if (mForeground != null) {
            mForeground.setHotspot(x, y);
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void setForeground(Drawable foreground) {

        if (mHasNativeBackground) {
            super.setForeground(foreground);
            return;
        }

        if (mForeground != foreground) {
            if (mForeground != null) {
                mForeground.setCallback(null);
                unscheduleDrawable(mForeground);
            }

            mForeground = foreground;

            if (foreground != null) {
                setWillNotDraw(false);
                foreground.setCallback(this);
                // Drawable.setLayoutDirection() is hidden on previous platforms.
                //foreground.setLayoutDirection(ViewCompat.getLayoutDirection(this));
                if (foreground.isStateful()) {
                    foreground.setState(getDrawableState());
                }
            } else {
                setWillNotDraw(true);
            }
            requestLayout();
            invalidate();
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Drawable getForeground() {

        if (mHasNativeBackground) {
            return super.getForeground();
        }

        return mForeground;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        super.onLayout(changed, left, top, right, bottom);

        if (mHasNativeBackground) {
            return;
        }

        mForegroundBoundsChanged = true;
    }

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

        if (mHasNativeBackground) {
            return;
        }

        mForegroundBoundsChanged = true;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void draw(@NonNull Canvas canvas) {
        super.draw(canvas);

        if (mHasNativeBackground) {
            return;
        }

        if (mForeground != null) {

            final Drawable foreground = mForeground;

            if (mForegroundBoundsChanged) {

                mForegroundBoundsChanged = false;
                Rect selfBounds = mSelfBounds;
                Rect overlayBounds = mOverlayBounds;

                int w = getRight() - getLeft();
                int h = getBottom() - getTop();

                if (mForegroundInPadding) {
                    selfBounds.set(0, 0, w, h);
                } else {
                    selfBounds.set(getPaddingLeft(), getPaddingTop(), w - getPaddingRight(),
                            h - getPaddingBottom());
                }

                int layoutDirection = ViewCompat.getLayoutDirection(this);
                GravityCompat.apply(mForegroundGravity, foreground.getIntrinsicWidth(),
                        foreground.getIntrinsicHeight(), selfBounds, overlayBounds,
                        layoutDirection);
                foreground.setBounds(overlayBounds);
            }

            foreground.draw(canvas);
        }
    }
}