Achartengine折线图实现背景渐变效果

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最近一个项目里面要实现这种UI界面，由于之前没做过类似的表格，当时就无从下手。但从网上了解到Achartengine开源框架可以实现很多表格图，然后就下载jar包集成到自己的项目里面。

慢慢的研究下，还是把表格画出来了。原生的Achartengine里面有mRenderer.setFillBelowLine(true)和mRenderer.setFillBelowLineColor(Color.parseColor("#ffE3A505"))这个2方法来实现这下面的背景颜色设置，mRenderer是单条曲线渲染器(XYSeriesRenderer)。但是原生的背景颜色设置是单一的，没有我要的这样颜色的渐变效果。我要强烈的吐槽下，为什么没有渐变的效果！！！

没有办法，只能站在巨人的肩膀上修改它的源码了。记住，在看它的源码的时候千万不要从头开始看，我感觉那样没有必要。我们只是要实现一个背景颜色渐变的效果，只要找准入口的位子就事半功倍了。mRenderer.setFillBelowLineColor(Color.parseColor("#ffE3A505"))是它用来设置背景颜色的方法，那我们就从这里入口，看它是怎么把背景颜色画出来的。

点到最后就这样的，我们做的就是setColor()的工作。既然我们设置的颜色，它肯定要取出来啊。它上面果然有个getColor()的方法，继续走近去，看那个地方调用了这个方法。

哇！！！整个框架里面就一个地方调用了这个方法，减少了我很多的麻烦。再看看里面都是些什么鬼。

public void drawSeries(Canvas canvas, Paint paint, List<Float> points, XYSeriesRenderer renderer,
      float yAxisValue, int seriesIndex, int startIndex) {
    float lineWidth = paint.getStrokeWidth();
    paint.setStrokeWidth(renderer.getLineWidth());
    final FillOutsideLine[] fillOutsideLine = renderer.getFillOutsideLine();

    for (FillOutsideLine fill : fillOutsideLine) {
      if (fill.getType() != FillOutsideLine.Type.NONE) {
        paint.setColor(fill.<span style="color:#ff0000;background-color: rgb(255, 255, 255);">getColor()</span>);
        // TODO: find a way to do area charts without duplicating data
        List<Float> fillPoints = new ArrayList<Float>();
        int[] range = fill.getFillRange();
        if (range == null) {
          fillPoints.addAll(points);
        } else {
          if (points.size() > range[0] * 2 && points.size() > range[1] * 2) {
            fillPoints.addAll(points.subList(range[0] * 2, range[1] * 2));
          }
        }

        final float referencePoint;
        switch (fill.getType()) {
        case BOUNDS_ALL:
          referencePoint = yAxisValue;
          break;
        case BOUNDS_BELOW:
          referencePoint = yAxisValue;
          break;
        case BOUNDS_ABOVE:
          referencePoint = yAxisValue;
          break;
        case BELOW:
          referencePoint = canvas.getHeight();
          break;
        case ABOVE:
          referencePoint = 0;
          break;
        default:
          throw new RuntimeException(
              "You have added a new type of filling but have not implemented.");
        }
        if (fill.getType() == FillOutsideLine.Type.BOUNDS_ABOVE
            || fill.getType() == FillOutsideLine.Type.BOUNDS_BELOW) {
          List<Float> boundsPoints = new ArrayList<Float>();
          boolean add = false;
          int length = fillPoints.size();
          if (length > 0 && fill.getType() == FillOutsideLine.Type.BOUNDS_ABOVE
              && fillPoints.get(1) < referencePoint
              || fill.getType() == FillOutsideLine.Type.BOUNDS_BELOW
              && fillPoints.get(1) > referencePoint) {
            boundsPoints.add(fillPoints.get(0));
            boundsPoints.add(fillPoints.get(1));
            add = true;
          }

          for (int i = 3; i < length; i += 2) {
            float prevValue = fillPoints.get(i - 2);
            float value = fillPoints.get(i);

            if (prevValue < referencePoint && value > referencePoint || prevValue > referencePoint
                && value < referencePoint) {
              float prevX = fillPoints.get(i - 3);
              float x = fillPoints.get(i - 1);
              boundsPoints.add(prevX + (x - prevX) * (referencePoint - prevValue)
                  / (value - prevValue));
              boundsPoints.add(referencePoint);
              if (fill.getType() == FillOutsideLine.Type.BOUNDS_ABOVE && value > referencePoint
                  || fill.getType() == FillOutsideLine.Type.BOUNDS_BELOW && value < referencePoint) {
                i += 2;
                add = false;
              } else {
                boundsPoints.add(x);
                boundsPoints.add(value);
                add = true;
              }
            } else {
              if (add || fill.getType() == FillOutsideLine.Type.BOUNDS_ABOVE
                  && value < referencePoint || fill.getType() == FillOutsideLine.Type.BOUNDS_BELOW
                  && value > referencePoint) {
                boundsPoints.add(fillPoints.get(i - 1));
                boundsPoints.add(value);
              }
            }
          }

          fillPoints.clear();
          fillPoints.addAll(boundsPoints);
        }
        int length = fillPoints.size();
        if (length > 0) {
          fillPoints.set(0, fillPoints.get(0) + 1);
          fillPoints.add(fillPoints.get(length - 2));
          fillPoints.add(referencePoint);
          fillPoints.add(fillPoints.get(0));
          fillPoints.add(fillPoints.get(length + 1));
          for (int i = 0; i < length + 4; i += 2) {
            if (fillPoints.get(i + 1) < 0) {
              fillPoints.set(i + 1, 0f);
            }
          }

          <span style="color:#ff0000;">paint.setStyle(Style.FILL);</span>
          <span style="background-color: rgb(255, 255, 255);"><span style="color:#ff0000;">drawPath(canvas, fillPoints, paint, true);</span></span>
        }
      }
    }
    paint.setColor(renderer.getColor());
    paint.setStyle(Style.STROKE);
    drawPath(canvas, points, paint, false);
    paint.setStrokeWidth(lineWidth);
  }

我把改好的源码jar包放在了云盘里，地址 https://yunpan.cn/cP4tqsDEUjtkY  访问密码 e4a4我的资源里面也有，里面增加背景颜色渐变效果的API，只需调用 Yaohui.setYaohui(true)和 Yaohui.setLg(new LinearGradient(130, 100, 130, 250, colors, positions, TileMode.CLAMP))就可以实现渐变的效果了，但是前提是一定要设置mRenderer.setFillBelowLine(true)，要不是没有效果的。好了就到了，虽然写的不是特别好，但是大家觉得有用的话希望顶一下，谢谢啦！！！

Achartengine折线图实现背景渐变效果

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原文地址：http://blog.csdn.net/qq_34670639/article/details/51354054