如何修改作为RecyclerView Item卡片背景的Drawable XML中元素的颜色？

Hey there! Let's cover both static (XML-based) and dynamic (code-based) ways to update the colors in your layer-list drawable, since you're using it as a RecyclerView item background:

1. Static Color Changes (Directly in XML) #

Your current drawable uses a layer-list with a primary color background. To update this statically:

Update the main background color #

You can either replace the existing color reference with a new one, or use a raw hex color value:

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <!-- Option 1: Use a color resource -->
    <item android:drawable="@color/your_new_primary_color" android:id="@+id/background_color"/>
    
    <!-- OR Option 2: Use a hex color directly -->
    <!-- <item android:drawable="#FF2196F3" android:id="@+id/background_color"/> -->

    <item android:top="200dp" android:bottom="-300dp" android:left="0dp" android:right="-300dp">
        <rotate android:fromDegrees="-10" android:pivotX="0%" android:pivotY="100%">
            <!-- Assuming your shape is a rectangle; add a solid color here -->
            <shape android:shape="rectangle">
                <solid android:color="@color/your_rotate_shape_color"/>
                <!-- Optional: Add corners, stroke, etc. -->
            </shape>
        </rotate>
    </item>
</layer-list>

2. Dynamic Color Changes (In Kotlin/Java Code) #

Since you've assigned an android:id to the main background item, you can modify its color at runtime (perfect for RecyclerView items that need dynamic theming, like selection states).

In your RecyclerView Adapter's onBindViewHolder method: #

Kotlin Example:

// Get the layer drawable from the item view
val layerDrawable = holder.itemView.background as LayerDrawable
// Find the specific layer by ID
val backgroundLayer = layerDrawable.findDrawableByLayerId(R.id.background_color) as ColorDrawable
// Update the color
backgroundLayer.color = ContextCompat.getColor(holder.itemView.context, R.color.dynamic_color)

// If you also need to update the rotated shape's color:
// 1. First add an ID to the <item> containing the rotate element in XML:
// <item android:id="@+id/rotated_shape_item" android:top="200dp" ...>
// 2. Then in code:
val rotatedShapeLayer = layerDrawable.findDrawableByLayerId(R.id.rotated_shape_item) as RotateDrawable
val shapeDrawable = rotatedShapeLayer.drawable as GradientDrawable
shapeDrawable.setColor(ContextCompat.getColor(holder.itemView.context, R.color.dynamic_shape_color))

Java Example:

// Get the layer drawable from the item view
LayerDrawable layerDrawable = (LayerDrawable) holder.itemView.getBackground();
// Find the specific layer by ID
ColorDrawable backgroundLayer = (ColorDrawable) layerDrawable.findDrawableByLayerId(R.id.background_color);
// Update the color
backgroundLayer.setColor(ContextCompat.getColor(holder.itemView.getContext(), R.color.dynamic_color));

// To update the rotated shape's color (after adding an ID to its parent <item>):
RotateDrawable rotatedShapeLayer = (RotateDrawable) layerDrawable.findDrawableByLayerId(R.id.rotated_shape_item);
GradientDrawable shapeDrawable = (GradientDrawable) rotatedShapeLayer.getDrawable();
shapeDrawable.setColor(ContextCompat.getColor(holder.itemView.getContext(), R.color.dynamic_shape_color));

Key Notes: #

• Make sure you cast the drawables correctly (e.g., ColorDrawable for solid color items, GradientDrawable for shape elements).
• For dynamic changes, always use ContextCompat.getColor() to handle compatibility across Android versions.

内容的提问来源于stack exchange，提问作者Varun Joshi