Android 使用远程下载的.9图片

众所周知，android的.9图片可以实现矢量拉伸，但是资源文件却被限制在本地而无法使用远端文件。

作者今天遇到了同样的问题，查看了一下android源码，发现NinePatch和NinePatchDrawable这两个玩意儿，.9图片最终的绘制是通过他们来实现的，那么问题来了，我只需要new出这两个东西不就OK了吗？so，我查看了一下构造函数，别的都好说，Chunk是什么鬼？还是个32字节的东西，按照作者经验，.9的黑边框应该是被解析成了这32字节的数据，然后Drawable按照这个规则来绘制画板的。查验多放资料，作者搞出了下面这个方法，你们可以参考下，可以生成Chunk字节数组，用他们就可以实现远端图片的.9了。

public static byte[] readChunk(Bitmap resourceBmp) throws IOException {
   final int BM_W = resourceBmp.getWidth();
   final int BM_H = resourceBmp.getHeight();

   int xPointCount = 0;
   int yPointCount = 0;
   int xBlockCount = 0;
   int yBlockCount = 0;

   ByteArrayOutputStream bao = new ByteArrayOutputStream();
   for (int i = 0; i < 32; i++) {
      bao.write(0);
   }

   {
      int[] pixelsTop = new int[BM_W - 2];
      resourceBmp.getPixels(pixelsTop, 0, BM_W, 1, 0, BM_W - 2, 1);
      boolean topFirstPixelIsBlack = pixelsTop[0] == Color.BLACK;
      boolean topLastPixelIsBlack = pixelsTop[pixelsTop.length - 1] == Color.BLACK;
      int tmpLastColor = Color.TRANSPARENT;
      for (int i = 0, len = pixelsTop.length; i < len; i++) {
         if (tmpLastColor != pixelsTop[i]) {
            xPointCount++;
            writeInt(bao, i);
            tmpLastColor = pixelsTop[i];
         }
      }
      if (topLastPixelIsBlack) {
         xPointCount++;
         writeInt(bao, pixelsTop.length);
      }
      xBlockCount = xPointCount + 1;
      if (topFirstPixelIsBlack) {
         xBlockCount--;
      }
      if (topLastPixelIsBlack) {
         xBlockCount--;
      }
   }

   {
      int[] pixelsLeft = new int[BM_H - 2];
      resourceBmp.getPixels(pixelsLeft, 0, 1, 0, 1, 1, BM_H - 2);
      boolean firstPixelIsBlack = pixelsLeft[0] == Color.BLACK;
      boolean lastPixelIsBlack = pixelsLeft[pixelsLeft.length - 1] == Color.BLACK;
      int tmpLastColor = Color.TRANSPARENT;
      for (int i = 0, len = pixelsLeft.length; i < len; i++) {
         if (tmpLastColor != pixelsLeft[i]) {
            yPointCount++;
            writeInt(bao, i);
            tmpLastColor = pixelsLeft[i];
         }
      }
      if (lastPixelIsBlack) {
         yPointCount++;
         writeInt(bao, pixelsLeft.length);
      }
      yBlockCount = yPointCount + 1;
      if (firstPixelIsBlack) {
         yBlockCount--;
      }
      if (lastPixelIsBlack) {
         yBlockCount--;
      }
   }

   {
      for (int i = 0; i < xBlockCount * yBlockCount; i++) {
         writeInt(bao, NO_COLOR);
      }
   }

   byte[] data = bao.toByteArray();
   data[0] = 1;
   data[1] = (byte) xPointCount;
   data[2] = (byte) yPointCount;
   data[3] = (byte) (xBlockCount * yBlockCount);
   dealPaddingInfo(resourceBmp, data);
   return data;
}

private static void dealPaddingInfo(Bitmap bm, byte[] data) {
   { // padding left & padding right
      int[] bottomPixels = new int[bm.getWidth() - 2];
      bm.getPixels(bottomPixels, 0, bottomPixels.length, 1,
            bm.getHeight() - 1, bottomPixels.length, 1);
      for (int i = 0; i < bottomPixels.length; i++) {
         if (Color.BLACK == bottomPixels[i]) { // padding left
            writeInt(data, 12, i);
            break;
         }
      }
      for (int i = bottomPixels.length - 1; i >= 0; i--) {
         if (Color.BLACK == bottomPixels[i]) { // padding right
            writeInt(data, 16, bottomPixels.length - i - 2);
            break;
         }
      }
   }
   { // padding top & padding bottom
      int[] rightPixels = new int[bm.getHeight() - 2];
      bm.getPixels(rightPixels, 0, 1, bm.getWidth() - 1, 0, 1,
            rightPixels.length);
      for (int i = 0; i < rightPixels.length; i++) {
         if (Color.BLACK == rightPixels[i]) { // padding top
            writeInt(data, 20, i);
            break;
         }
      }
      for (int i = rightPixels.length - 1; i >= 0; i--) {
         if (Color.BLACK == rightPixels[i]) { // padding bottom
            writeInt(data, 24, rightPixels.length - i - 2);
            break;
         }
      }
   }
}

private static void writeInt(OutputStream out, int v) throws IOException {
   out.write((v >> 0) & 0xFF);
   out.write((v >> 8) & 0xFF);
   out.write((v >> 16) & 0xFF);
   out.write((v >> 24) & 0xFF);
}

private static void writeInt(byte[] b, int offset, int v) {
   b[offset + 0] = (byte) (v >> 0);
   b[offset + 1] = (byte) (v >> 8);
   b[offset + 2] = (byte) (v >> 16);
   b[offset + 3] = (byte) (v >> 24);
}

private static int getInt(byte[] bs, int from) {
   int b1 = bs[from + 0];
   int b2 = bs[from + 1];
   int b3 = bs[from + 2];
   int b4 = bs[from + 3];
   int i = b1 | (b2 << 8)  | (b3 << 16) | b4 << 24;
   return i;
}

调用的方法也很简单：

NinePatch ninePatch = null;
try {
    ninePatch = new NinePatch(bitmap,NinePatchUtils.readChunk(bitmap));
} catch (IOException e) {
    e.printStackTrace();
}
NinePatchDrawable ninePatchDrawable = new NinePatchDrawable(getResources(),ninePatch);
imageView.setBackgroundDrawable(ninePatchDrawable);

如此，大功告成。

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