Creating a pie chart view on Android

In this post I shall be writing about how you can create a pie chart view by drawing on Canvas.

Without wasting any more time lets start.
First thing that we have to do is to create a new view class lets call it PieChartView and extend with View class.
Now, I will be drawing each section of pie chart with a different colour, so I also create an array of few colour codes.
We will also require a Paint object, so lets do that too.
Besides all these lets create a 2 Dimensional array of App Name, and the Percentage. This will serve as a dummy data to plot.

So our code will look like this now:

Now lets override onSizeChanged(int nw, int nh, int ow, int oh) method. Here we will initialize paint object, create a Rectangle object, within which we will draw, and select dimension for circle, whose width and height will be same.

Lets create two other methods, setTextSize & setData, we will need them later on.

So now our code looks like this:

All small things are set now, its time to override the onDraw method now.

Here is what we will do to draw arc:

  1. Go through each data that will be drawn.
  2. For the percentage calculate how many degrees will it cover.
  3. For every section, calculate start & end degree.
  4. Draw Arc using these degrees.

Next is to write text. These are the things which shall be done for same.

  1. Go through each data that will be drawn.
  2. For the percentage calculate how many degrees will it cover.
  3. Convert degrees to radian, since Java Sin, Cos classes work on Radian.
  4. For each degree calculate the point that will lie on arc, below is the diagram to understand the same.
  5. Calculate the width of text and subtract that from X coordinate while drawing.
  6. Similarly adjust the height of it.

Here is the diagram to understand the coordinate from degree.

So finally our code looks like this:

And here is how our Pie Chart looks like.

Hope you liked it.
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