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In this video we'll see how we can use price information to make our chart fit better on the screen!
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When we look at our data on one
of the shorter time frames,
0:00
it kinda just looks like a line.
0:02
To fix this, instead of plotting our
points just as they are, let's modify
0:04
our graph to have the lowest value of the
subset be the bottom of the screen, and
0:09
the highest value be at the top.
0:13
That way, no matter what time frame we
choose, our data will be easily visible.
0:15
To do this let's create
two new float fields,
0:20
for the maxPrice and the minPrice.
0:27
Then, inside the original
show last function,
0:31
below where we update our subset,
let's call a method that doesn't exist yet
0:34
called updateMaxAndMin.
0:39
And then lets use alt Enter to create it.
0:45
Inside our new function,
let's start off by setting maxPrice equal
0:48
to something much lower than
anything in our data like, -1.
0:53
And let's also set minPrice equal to
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something much higher, like 99999.
1:01
Then we just need to loop through our
subset and update our max and min.
1:06
So let's type, for (StockData) which
1:10
we'll call stockData and subset.
1:15
And for each stockData,
1:20
if stockData.high is
greater than maxPrice,
1:23
then let's set maxPrice
equal to stockData.high.
1:29
Likewise, if stockData.low
is less than minPrice,
1:37
let's set minPrice equal to stockData.low.
1:44
Nice, now that we've got the maximum and
minimum of our subset,
1:50
let's see if we can't use those to
make our chart look a lot nicer.
1:53
To do this, let's create a function named,
getYPosition, that takes on a price and
1:56
returns the y-coordinate for that price.
2:01
So let's add some room
after our on draw call and
2:04
then type private float getYPosition,
2:08
which takes in another float named price.
2:12
Then, inside this function, let's start
off by figuring out where we fall
2:19
between our minPrice and our maxPrice.
2:23
So let's create a new
float named scaleFactorY,
2:26
and set it equal to, in parentheses,
2:32
price minus minPrice divided by,
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also in parentheses,
maxPrice minus minPrice.
2:40
So the y-position of our price
2:45
would just be the height of
our canvas times scaleFactorY.
2:49
But since our canvas is flipped,
2:53
what we really need is
the height minus that value.
2:55
So let's return,
3:00
height minus height times scaleFactorY.
3:03
And back inside our call to drawRect,
3:09
instead of passing in height
minus stockData.high,
3:12
let's call our new getYPposition
function and pass in stockData.high.
3:18
And let's do the same thing for
stockData.low.
3:25
Awesome.
3:31
For the last step, since we now need
a max and min to draw anything,
3:32
we need to call our update max and
min function and our constructor.
3:35
So inside our constructor, let's delete
the line where we set subset equal to data
3:39
and instead let's just call
showLast with no parameters.
3:45
Which will update our subset and
our max and min, perfect.
3:50
Now let's run the app and
see what happens.
3:53
Looks good so far.
4:00
It's the same graph as before, but
now it's using a lot more of the screen.
4:01
And if we click through
to the other views.
4:04
They all look just as good.
4:11
In the next video,
4:13
we'll start turning these boring green
bars into exciting colorful candlesticks.
4:14
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