如何实现 Pre-lollipop 的 Material-design Elevation

Question

Google 展示了一些在 Lollipop 上显示海拔效果的好方法 here。

android:elevation="2dp"

对于按钮，

android:stateListAnimator="@anim/button_state_list_animator"

如何在没有第 3 方库的情况下模拟 Lollipop 之前版本的提升效果？

Answer 1

你不能用官方方法模仿 pre-Lollipop 上的高度。

您可以使用一些可绘制对象在您的组件中制作阴影。 Google例如在CardView中使用这种方式。

ViewCompat.setElevation(View, int) 目前仅在 API21+ 上创建阴影。如果查看后面的代码，这个方法调用：

API 21+:

  @Override
    public void setElevation(View view, float elevation) {
        ViewCompatLollipop.setElevation(view, elevation);
    }

API < 21

@Override
public void setElevation(View view, float elevation) {

}

Answer 2

要为 Lollipop 之前的设备带来动态的动画阴影，您必须：

将视图的黑色形状绘制到位图
使用高程作为半径模糊该形状。您可以使用 RenderScript 来做到这一点。这与 Lollipop 使用的方法不完全相同，但效果很好，并且很容易添加到现有视图中。
在视图下方画出那个模糊的形状。可能最好的地方是 drawChild 方法。您还必须覆盖 setElevation 和 setTranslationZ，覆盖布局中的子视图绘制，关闭 clip-to-padding 并实现状态动画。

工作量很大，但它提供了带有响应动画的最佳外观、动态阴影。我不确定您为什么要在没有第三方库的情况下实现这一目标。如果您愿意，您可以分析 Carbon 的来源并移植您想要在您的应用程序中拥有的部分：

Shadow generation

private static void blurRenderScript(Bitmap bitmap, float radius) {
    Allocation inAllocation = Allocation.createFromBitmap(renderScript, bitmap,
            Allocation.MipmapControl.MIPMAP_NONE, Allocation.USAGE_SCRIPT);
    Allocation outAllocation = Allocation.createTyped(renderScript, inAllocation.getType());

    blurShader.setRadius(radius);
    blurShader.setInput(inAllocation);
    blurShader.forEach(outAllocation);

    outAllocation.copyTo(bitmap);
}

public static Shadow generateShadow(View view, float elevation) {
    if (!software && renderScript == null) {
        try {
            renderScript = RenderScript.create(view.getContext());
            blurShader = ScriptIntrinsicBlur.create(renderScript, Element.U8_4(renderScript));
        } catch (RSRuntimeException ignore) {
            software = true;
        }
    }

    ShadowView shadowView = (ShadowView) view;
    CornerView cornerView = (CornerView) view;
    boolean isRect = shadowView.getShadowShape() == ShadowShape.RECT ||
            shadowView.getShadowShape() == ShadowShape.ROUND_RECT && cornerView.getCornerRadius() < view.getContext().getResources().getDimension(R.dimen.carbon_1dip) * 2.5;

    int e = (int) Math.ceil(elevation);
    Bitmap bitmap;
    if (isRect) {
        bitmap = Bitmap.createBitmap(e * 4 + 1, e * 4 + 1, Bitmap.Config.ARGB_8888);

        Canvas shadowCanvas = new Canvas(bitmap);
        paint.setStyle(Paint.Style.FILL);
        paint.setColor(0xff000000);

        shadowCanvas.drawRect(e, e, e * 3 + 1, e * 3 + 1, paint);

        blur(bitmap, elevation);

        return new NinePatchShadow(bitmap, elevation);
    } else {
        bitmap = Bitmap.createBitmap((int) (view.getWidth() / SHADOW_SCALE + e * 2), (int) (view.getHeight() / SHADOW_SCALE + e * 2), Bitmap.Config.ARGB_8888);

        Canvas shadowCanvas = new Canvas(bitmap);
        paint.setStyle(Paint.Style.FILL);
        paint.setColor(0xff000000);

        if (shadowView.getShadowShape() == ShadowShape.ROUND_RECT) {
            roundRect.set(e, e, (int) (view.getWidth() / SHADOW_SCALE - e), (int) (view.getHeight() / SHADOW_SCALE - e));
            shadowCanvas.drawRoundRect(roundRect, e, e, paint);
        } else {
            int r = (int) (view.getWidth() / 2 / SHADOW_SCALE);
            shadowCanvas.drawCircle(r + e, r + e, r, paint);
        }

        blur(bitmap, elevation);

        return new Shadow(bitmap, elevation);
    }
}

Drawing a view with a shadow

@Override
protected boolean drawChild(Canvas canvas, View child, long drawingTime) {
    if (!child.isShown())
        return super.drawChild(canvas, child, drawingTime);

    if (!isInEditMode() && child instanceof ShadowView && Build.VERSION.SDK_INT <= Build.VERSION_CODES.KITKAT_WATCH) {
        ShadowView shadowView = (ShadowView) child;
        Shadow shadow = shadowView.getShadow();
        if (shadow != null) {
            paint.setAlpha((int) (ShadowGenerator.ALPHA * ViewHelper.getAlpha(child)));

            float childElevation = shadowView.getElevation() + shadowView.getTranslationZ();

            float[] childLocation = new float[]{(child.getLeft() + child.getRight()) / 2, (child.getTop() + child.getBottom()) / 2};
            Matrix matrix = carbon.internal.ViewHelper.getMatrix(child);
            matrix.mapPoints(childLocation);

            int[] location = new int[2];
            getLocationOnScreen(location);
            float x = childLocation[0] + location[0];
            float y = childLocation[1] + location[1];
            x -= getRootView().getWidth() / 2;
            y += getRootView().getHeight() / 2;   // looks nice
            float length = (float) Math.sqrt(x * x + y * y);

            int saveCount = canvas.save(Canvas.MATRIX_SAVE_FLAG);
            canvas.translate(
                    x / length * childElevation / 2,
                    y / length * childElevation / 2);
            canvas.translate(
                    child.getLeft(),
                    child.getTop());

            canvas.concat(matrix);
            canvas.scale(ShadowGenerator.SHADOW_SCALE, ShadowGenerator.SHADOW_SCALE);
            shadow.draw(canvas, child, paint);
            canvas.restoreToCount(saveCount);
        }
    }

    if (child instanceof RippleView) {
        RippleView rippleView = (RippleView) child;
        RippleDrawable rippleDrawable = rippleView.getRippleDrawable();
        if (rippleDrawable != null && rippleDrawable.getStyle() == RippleDrawable.Style.Borderless) {
            int saveCount = canvas.save(Canvas.MATRIX_SAVE_FLAG);
            canvas.translate(
                    child.getLeft(),
                    child.getTop());
            rippleDrawable.draw(canvas);
            canvas.restoreToCount(saveCount);
        }
    }

    return super.drawChild(canvas, child, drawingTime);
}

Elevation API backported to pre-Lollipop

private float elevation = 0;
private float translationZ = 0;
private Shadow shadow;

@Override
public float getElevation() {
    return elevation;
}

public synchronized void setElevation(float elevation) {
    if (elevation == this.elevation)
        return;
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP)
        super.setElevation(elevation);
    this.elevation = elevation;
    if (getParent() != null)
        ((View) getParent()).postInvalidate();
}

@Override
public float getTranslationZ() {
    return translationZ;
}

public synchronized void setTranslationZ(float translationZ) {
    if (translationZ == this.translationZ)
        return;
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP)
        super.setTranslationZ(translationZ);
    this.translationZ = translationZ;
    if (getParent() != null)
        ((View) getParent()).postInvalidate();
}

@Override
public ShadowShape getShadowShape() {
    if (cornerRadius == getWidth() / 2 && getWidth() == getHeight())
        return ShadowShape.CIRCLE;
    if (cornerRadius > 0)
        return ShadowShape.ROUND_RECT;
    return ShadowShape.RECT;
}

@Override
public void setEnabled(boolean enabled) {
    super.setEnabled(enabled);
    setTranslationZ(enabled ? 0 : -elevation);
}

@Override
public Shadow getShadow() {
    float elevation = getElevation() + getTranslationZ();
    if (elevation >= 0.01f && getWidth() > 0 && getHeight() > 0) {
        if (shadow == null || shadow.elevation != elevation)
            shadow = ShadowGenerator.generateShadow(this, elevation);
        return shadow;
    }
    return null;
}

@Override
public void invalidateShadow() {
    shadow = null;
    if (getParent() != null && getParent() instanceof View)
        ((View) getParent()).postInvalidate();
}

Answer 3

你可以用官方的方法模仿pre-Lollipop上的高度

我使用

达到同样的效果

  android:background="@android:drawable/dialog_holo_light_frame"

我的测试输出：

参考 -

感谢用户@Repo..

更新：如果你想改变这个drawable的颜色试试@Irfan下面的回答↓

Answer 4

创建一个 9-patch 图像，在图像上定义可拉伸的补丁，周围有阴影。

将此 9 色补丁图像添加为带填充的按钮背景，以便阴影可见。

您可以找到一些预定义的 9 补丁 (.9.png) 图片 here or here，您可以从那里 select、自定义并复制到项目的可绘制对象中。

Answer 5

您可以使用卡片视图破解它：

<android.support.v7.widget.CardView
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    android:id="@+id/btnGetStuff"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    card_view:cardCornerRadius="4dp"
    card_view:cardBackgroundColor="@color/accent"
    >
    <!-- you could also add image view here for icon etc. -->
    <TextView
        android:id="@+id/txtGetStuff"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="@dimen/textSize_small"
        android:textColor="@color/primary_light"
        android:freezesText="true"
        android:text="Get Stuff"
        android:maxWidth="120dp"
        android:singleLine="true"
        android:ellipsize="end"
        android:maxLines="1"
        /></android.support.v7.widget.CardView>

或者看看使用这个第三方库：https://github.com/rey5137/Material (see wiki article on button https://github.com/rey5137/Material/wiki/Button)

Answer 6

你可以通过像这样声明一个可绘制对象来轻松地模拟它 -

shadow.xml

<?xml version="1.0" encoding="utf-8"?>
<shape
    xmlns:android="http://schemas.android.com/apk/res/android"

    >

    <gradient android:type="linear" android:angle="270" android:startColor="#b6b6b6" android:endColor="#ffffff"/>


</shape>

并在你的主要 xml 中使用它，比如 -

 android:background="@drawable/shadow"

Answer 7

添加@Ranjith Kumar 的回答

要为可绘制对象添加背景颜色（例如按钮背景颜色），我们需要以编程方式获取可绘制对象。

首先获取drawable

Drawable drawable = getResources().getDrawable(android.R.drawable.dialog_holo_light_frame);

设置颜色

drawable.setColorFilter(new PorterDuffColorFilter(getResources().getColor(R.color.color_primary), PorterDuff.Mode.MULTIPLY));

然后将其设置为视图。

view.setBackgroundDrawable(drawable);

以防有人搜索。

如何实现 Pre-lollipop 的 Material-design Elevation

How to implement the Material-design Elevation for Pre-lollipop

android

material-design

android-appcompat

android-elevation

Shadow generation

Drawing a view with a shadow

Elevation API backported to pre-Lollipop