Question

I need to center grid view horizontally in my android layout.xml. I have searched google for quite a while but didnt succeed in finding an answer.

I can only change gridview horizontal position by changing strechMode, but then my items are not near one another.
that i need is items be one near another (without spaces) and centered horizontally. I choose strechmode = none, so now my items are near one another, but they are on the left of the screen, i just want them to be centered horizontally.

Here is my layout xml:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
          android:layout_width="fill_parent" 
          android:layout_height="fill_parent"
          android:background="@drawable/background" 
          android:gravity="center">

<GridView android:id="@+id/lw_gridview" 
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:numColumns="3" 
          android:columnWidth="48dp"
          android:horizontalSpacing="0dp"
          android:verticalSpacing="0dp"
          android:stretchMode="none"
          />


</LinearLayout>

Here is fragment of an image which is set on gridview by image adapter:

imageView = new ImageView(context);
imageView.setLayoutParams(new GridView.LayoutParams(48,48)); //on medium density
imageView.setScaleType(ImageView.ScaleType.CENTER);
imageView.setPadding(0, 0, 0, 0);

How can i succeed?

Answer 1

I centered my grid view manually, by calculating and setting its padding. Here’s what my onCreate does:

• find out width of the screen and screen density
• convert constant values for item width and spacing from DIP to pixels
• calculate number of columns I can fit.

Equation looks like this, numColumns is the only unknown:

numColumns * itemWidth + (numColumns - 1) * spacingBetweenItems + selectorPadding <= sreenWidth

• having numColumns, calculate how much horizontal space my grid view will actually need
• having actual width of grid view, set padding so that it ends up in the center of screen

OK, and here’s some code:

// Convert DIPs to pixels
DisplayMetrics metrics = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(metrics);
mSizePx = (int) Math.floor(SIZE_DIP * metrics.scaledDensity);
mSpacingPx = (int) Math.floor(SPACING_DIP * metrics.scaledDensity);

GridView gridview = (GridView) findViewById(R.id.gridview);
// Find out the extra space gridview uses for selector on its sides.
Rect p = new Rect();
gridview.getSelector().getPadding(p);
int selectorPadding = p.left + p.right;

// Determine the number of columns we can fit, given screen width,
// thumbnail width, and spacing between thumbnails.
int numColumns = (int) Math.floor(1f * (metrics.widthPixels - selectorPadding + mSpacingPx)
        / (mSizePx + mSpacingPx));

int contentWidth = numColumns * mSizePx; // Width of items
contentWidth += (numColumns - 1) * mSpacingPx; // Plus spaces between items
contentWidth += selectorPadding; // Plus extra space for selector on sides

// Now calculate amount of left and right margin so the grid gets
// centered. This is what we
// unfortunately cannot do with layout_width="wrap_content"
// and layout_gravity="center_horizontal"
int slack = metrics.widthPixels - contentWidth;

gridview.setNumColumns(numColumns);
gridview.setPadding(slack / 2, slack / 2, slack / 2, slack / 2);