Tim Tim - 28 days ago 7
Android Question

Fill remaining space with fixed aspect ratio surfaceview

I'd like to layout a view like the following, but I'm not sure how to go about doing so:


  • At the bottom of the screen is a regular view, with a fixed size (fill-width and some number of dp for height)

  • Filling the remaining vertical space, I would like to place a custom view which inherits from glSurfaceView, with the restriction that it must have a fixed aspect ratio, which will be programatically set, but known before the activity is created. (In this case assume it with be 2:3 w:h).



Here's a little picture of what I'm imagining:

.----------------------.
| .--------------. |
| b | | b |
| g | | g |
| | | |
| i | MySurface | i |
| m | View | m |
| a | | a |
| g | (2:3 w:h) | g |
| e | | e |
| *--------------* |
|.--------------------.|
|| ||
|| SomeOtherView ||
|| ||
|*--------------------*|
*----------------------*


As far as setting up the MySurfaceView, I assume that normal layout_width and layout_height are not going to help me, because I don't know the available screen size until after the screen has been partially laid out, and
SomeOtherView
has been placed.

Is there some function in
MySurfaceView
that I want to override, that for example will pass as arguments the available screen space, and let me decide how to set the width and height of the view?

Is 'inflation' the right term I'm looking for here? I think that has something to do with what I'm looking for, but I don't really know the terminology.

Updated below with the result of my research, and I think a possible correct solution.

Tim Tim
Answer Source

Did more research and I think I figured out what I need to do:

The function I was looking to override is onMeasure(int widthSpec, int heightSpec), which is called by the parent with suggestions for width and height (see View.MeasureSpec). I also set MySurfaceView to have a layout_width/height of wrap_content in the xml. Then when onMeasure gets called I can compute the available aspect ratio and set the width and height of my view as desired.

The second thing I did to make this work was to put my MySurfaceView inside of a FrameLayout as the only child. I originally had MySurfaceView in a RelativeLayout with the SomeOtherView from my image. The problem with the RelativeLayout, is that it would not negotiate the width/height in a way that allowed me to fix the aspect ratio.

onMeasure gets called multiple times during measuring, and the way RelativeLayout works is that it first asks the custom view for it's width without telling it the available height, and then later comes back and asks for the height, while the width is locked to what you specified in the first pass (MeasureSpec.EXACTLY). This makes it impossible to generate a view of a certain ratio, as you must confirm the width before knowing the available height.

Once inside of the FrameLayout, I didn't have this problem, as the MeasureSpecs passed to onMeasure only ever had the restriction AT_MOST. This means I was free to change the width and height during every pass of onMeasure, and so I could end up calculating my aspect ratio as desired given the available area.

Haven't confirmed yet that this works for all cases, but hopefully this will help someone.