Android画板开发之添加背景和保存画板内容为图片

override fun onDraw(canvas: Canvas) {
    super.onDraw(canvas)

    //先绘制颜色作为背景
    canvas.drawColor(Color.BLACK)

    //画出缓存bitmap的内容
    canvas.drawBitmap(mBufferBitmap,0f,0f,null)

  }

public void setBackgroundDrawable(Drawable background) {
    computeOpaqueFlags();

    if (background == mBackground) {
      return;
    }

    boolean requestLayout = false;

    mBackgroundResource = 0;
    ......
    if (background != null) {
      ......


      mBackground = background;


      applyBackgroundTint();

      ...
    } else {
      /* Remove the background */
      mBackground = null;
      .......
    }

    computeOpaqueFlags();

    if (requestLayout) {
      requestLayout();
    }

    mBackgroundSizeChanged = true;
    invalidate(true);
    invalidateOutline();
  }

private void drawBackground(Canvas canvas) {
    final Drawable background = mBackground;
    if (background == null) {
      return;
    }

    setBackgroundBounds();

    // Attempt to use a display list if requested.
    if (canvas.isHardwareAccelerated() && mAttachInfo != null
        && mAttachInfo.mHardwareRenderer != null) {
      mBackgroundRenderNode = getDrawableRenderNode(background, mBackgroundRenderNode);

      final RenderNode renderNode = mBackgroundRenderNode;
      if (renderNode != null && renderNode.isValid()) {
        setBackgroundRenderNodeProperties(renderNode);
        ((DisplayListCanvas) canvas).drawRenderNode(renderNode);
        return;
      }
    }

    final int scrollX = mScrollX;
    final int scrollY = mScrollY;
    if ((scrollX | scrollY) == 0) {
      background.draw(canvas);
    } else {
      canvas.translate(scrollX, scrollY);
      background.draw(canvas);
      canvas.translate(-scrollX, -scrollY);
    }
  }

 /**
   * 保存图片
   * @param path 保存图片的路径
   */
  fun save(path: String){

    if(!TextUtils.isEmpty(path)){

      val f = File(path)
      if(f.exists()){
        f.delete()
      }
      try{
        val out = FileOutputStream(f)
        //以90质量保存到输出到文件输出流
        mBufferBitmap.compress(Bitmap.CompressFormat.JPEG,90,out)

        out.flush()
        out.close()
      }catch (e:Exception){
        e.printStackTrace()
      }
    }
  }

init {
   mPaint.style = Paint.Style.STROKE //画笔为实心
   mPaint.color = Color.RED     //颜色
   mPaint.strokeCap = Paint.Cap.ROUND //笔触为圆形
   mPaint.strokeWidth = 10f      //画笔大小

    //开启缓存
    isDrawingCacheEnabled = true

  }

/**
 * 利用view自带方法获取bitmap，
 * 前提是开启setDrawingCacheEnabled(boolean enabled)
*/
  fun getCacheBitmap(): Bitmap{

    val bm = drawingCache
    val result = Bitmap.createBitmap(bm)
    //销毁build的缓存
    destroyDrawingCache()
    return result
  }

fun getBitmap(v: View): Bitmap{
    val bitmap = Bitmap.createBitmap(v.getWidth(), v.getHeight(), Bitmap.Config.ARGB_8888)
    val canvas = Canvas(bitmap)
    v.draw(canvas)
    return bitmap
  }