Android中如何将ImageView设置为可水平垂直重复的边框？

如图中内容图片所示，我该如何将ImageView设置为可在水平和垂直方向重复的边框？

实现方法 #

方法一：用BitmapDrawable实现全图重复边框

如果你的边框素材是可以无缝重复的图案，直接通过XML Drawable就能实现：

1. 将边框图片放入res/drawable目录
2. 创建res/drawable/repeat_border.xml文件：

<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <!-- 第一层：ImageView的内容图片 -->
    <item android:drawable="@drawable/your_content_image" />
    <!-- 第二层：重复的边框图案 -->
    <item>
        <bitmap
            android:src="@drawable/your_border_image"
            android:tileMode="repeat" />
    </item>
</layer-list>

3. 在布局中给ImageView设置该Drawable：

<ImageView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:src="@drawable/repeat_border" />

方法二：自定义Drawable实现边缘边框重复

如果需要边框仅在ImageView的上下左右边缘重复，而非覆盖整个视图，可自定义Drawable：

public class RepeatBorderDrawable extends Drawable {
    private final Bitmap mBorderBitmap;
    private final Paint mPaint;

    public RepeatBorderDrawable(Bitmap borderBitmap) {
        mBorderBitmap = borderBitmap;
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        // 设置重复渲染模式
        mPaint.setShader(new BitmapShader(borderBitmap, Shader.TileMode.REPEAT, Shader.TileMode.REPEAT));
    }

    @Override
    public void draw(@NonNull Canvas canvas) {
        Rect bounds = getBounds();
        int borderWidth = mBorderBitmap.getWidth();
        int borderHeight = mBorderBitmap.getHeight();

        // 绘制顶部边框
        canvas.drawRect(bounds.left, bounds.top, bounds.right, bounds.top + borderHeight, mPaint);
        // 绘制底部边框
        canvas.drawRect(bounds.left, bounds.bottom - borderHeight, bounds.right, bounds.bottom, mPaint);
        // 绘制左侧边框
        canvas.drawRect(bounds.left, bounds.top, bounds.left + borderWidth, bounds.bottom, mPaint);
        // 绘制右侧边框
        canvas.drawRect(bounds.right - borderWidth, bounds.top, bounds.right, bounds.bottom, mPaint);
    }

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

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

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

在代码中给ImageView设置：

Bitmap borderBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.your_border_image);
RepeatBorderDrawable borderDrawable = new RepeatBorderDrawable(borderBitmap);
// 设置边框为背景，src放内容图片
imageView.setBackground(borderDrawable);
imageView.setImageResource(R.drawable.your_content_image);

内容的提问来源于stack exchange，提问作者Rumiz