Android: How does GridView auto_fit find the number of columns?

Looking at the GridView source, it is clear that setting the padding and the height on your ImageView will not help you at all. When a column width is not specified, it just chooses a preset number of columns (2):

    private void determineColumns(int availableSpace) {

    ...

    if (mRequestedNumColumns == AUTO_FIT) {
        if (requestedColumnWidth > 0) {
            // Client told us to pick the number of columns
            mNumColumns = (availableSpace + requestedHorizontalSpacing) /
                    (requestedColumnWidth + requestedHorizontalSpacing);
        } else {
            // Just make up a number if we don't have enough info
            mNumColumns = 2;
        }
    } else {
        // We picked the columns
        mNumColumns = mRequestedNumColumns;
    }

    if (mNumColumns <= 0) {
        mNumColumns = 1;
    }

    ...

The solution is to measure your column size before setting the GridView's column width. Here is a quick way to measure Views offscreen:

public int measureCellWidth( Context context, View cell )
{

    // We need a fake parent
    FrameLayout buffer = new FrameLayout( context );
    android.widget.AbsListView.LayoutParams layoutParams = new  android.widget.AbsListView.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
    buffer.addView( cell, layoutParams);

    cell.forceLayout();
    cell.measure(1000, 1000);

    int width = cell.getMeasuredWidth();

    buffer.removeAllViews();

    return width;
}

And then you just set the GridView's column width:

gridView.setColumnWidth( width );

According to the android:numColumns documentation

auto_fit Display as many columns as possible to fill the available space.

So if you insert ImageViews with

padding set to zero

margin set to zero

layout_width set to wrap_content

layout_height set to wrap_content

The gridView should contain the maximum possible number of children

Keep in mind Your ImageViews maybe are getting scaled (: