Fixed aspect ratio View

For new users, here's a better non-code solution :

A new support library called Percent Support Library is available in Android SDK v22 (MinAPI is 7 me thinks, not sure) :

src : android-developers.blogspot.in

The Percent Support Library provides percentage based dimensions and margins and, new to this release, the ability to set a custom aspect ratio via app:aspectRatio. By setting only a single width or height and using aspectRatio, the PercentFrameLayout or PercentRelativeLayout will automatically adjust the other dimension so that the layout uses a set aspect ratio.

To include add this to your build.gradle :

compile 'com.android.support:percent:23.1.1'

Now wrap your view (the one that needs to be square) with a PercentRelativeLayout / PercentFrameLayout :

<android.support.percent.PercentRelativeLayout
         android:layout_width="match_parent"
         android:layout_height="wrap_content">
     <ImageView
         app:layout_aspectRatio="100%"
         app:layout_widthPercent="100%"/>
 </android.support.percent.PercentRelativeLayout>

You can see an example here.

I recently made a helper class for this very problem and wrote a blog post about it.

The meat of the code is as follows:

/**
 * Measure with a specific aspect ratio<br />
 * <br />
 * @param widthMeasureSpec The width <tt>MeasureSpec</tt> passed in your <tt>View.onMeasure()</tt> method
 * @param heightMeasureSpec The height <tt>MeasureSpec</tt> passed in your <tt>View.onMeasure()</tt> method
 * @param aspectRatio The aspect ratio to calculate measurements in respect to 
 */
public void measure(int widthMeasureSpec, int heightMeasureSpec, double aspectRatio) {
    int widthMode = MeasureSpec.getMode( widthMeasureSpec );
    int widthSize = widthMode == MeasureSpec.UNSPECIFIED ? Integer.MAX_VALUE : MeasureSpec.getSize( widthMeasureSpec );
    int heightMode = MeasureSpec.getMode( heightMeasureSpec );
    int heightSize = heightMode == MeasureSpec.UNSPECIFIED ? Integer.MAX_VALUE : MeasureSpec.getSize( heightMeasureSpec );

    if ( heightMode == MeasureSpec.EXACTLY && widthMode == MeasureSpec.EXACTLY ) {
        /* 
         * Possibility 1: Both width and height fixed
         */
        measuredWidth = widthSize;
        measuredHeight = heightSize;

    } else if ( heightMode == MeasureSpec.EXACTLY ) {
        /*
         * Possibility 2: Width dynamic, height fixed
         */
        measuredWidth = (int) Math.min( widthSize, heightSize * aspectRatio );
        measuredHeight = (int) (measuredWidth / aspectRatio);

    } else if ( widthMode == MeasureSpec.EXACTLY ) {
        /*
         * Possibility 3: Width fixed, height dynamic
         */
        measuredHeight = (int) Math.min( heightSize, widthSize / aspectRatio );
        measuredWidth = (int) (measuredHeight * aspectRatio);

    } else {
        /* 
         * Possibility 4: Both width and height dynamic
         */
        if ( widthSize > heightSize * aspectRatio ) {
            measuredHeight = heightSize;
            measuredWidth = (int)( measuredHeight * aspectRatio );
        } else {
            measuredWidth = widthSize;
            measuredHeight = (int) (measuredWidth / aspectRatio);
        }

    }
}

To not use third-party solution and considering the fact that both PercentFrameLayout and PercentRelativeLayout were deprecated in 26.0.0, I'd suggest you to consider using ConstraintLayout as a root layout for your grid items.

Your item_grid.xml might look like:

<android.support.constraint.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <ImageView
        android:id="@+id/imageview_item"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:scaleType="centerCrop"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintDimensionRatio="H,1:1" />

</android.support.constraint.ConstraintLayout>

As a result you get something like this:

I implemented FixedAspectRatioFrameLayout, so I can reuse it and have any hosted view be with fixed aspect ratio:

public class FixedAspectRatioFrameLayout extends FrameLayout
{
    private int mAspectRatioWidth;
    private int mAspectRatioHeight;

    public FixedAspectRatioFrameLayout(Context context)
    {
        super(context);
    }

    public FixedAspectRatioFrameLayout(Context context, AttributeSet attrs)
    {
        super(context, attrs);

        init(context, attrs);
    }

    public FixedAspectRatioFrameLayout(Context context, AttributeSet attrs, int defStyle)
    {
        super(context, attrs, defStyle);

        init(context, attrs);
    }

    private void init(Context context, AttributeSet attrs)
    {
        TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.FixedAspectRatioFrameLayout);

        mAspectRatioWidth = a.getInt(R.styleable.FixedAspectRatioFrameLayout_aspectRatioWidth, 4);
        mAspectRatioHeight = a.getInt(R.styleable.FixedAspectRatioFrameLayout_aspectRatioHeight, 3);

        a.recycle();
    }
    // **overrides**

    @Override protected void onMeasure (int widthMeasureSpec, int heightMeasureSpec)
    {
        int originalWidth = MeasureSpec.getSize(widthMeasureSpec);

        int originalHeight = MeasureSpec.getSize(heightMeasureSpec);

        int calculatedHeight = originalWidth * mAspectRatioHeight / mAspectRatioWidth;

        int finalWidth, finalHeight;

        if (calculatedHeight > originalHeight)
        {
            finalWidth = originalHeight * mAspectRatioWidth / mAspectRatioHeight; 
            finalHeight = originalHeight;
        }
        else
        {
            finalWidth = originalWidth;
            finalHeight = calculatedHeight;
        }

        super.onMeasure(
                MeasureSpec.makeMeasureSpec(finalWidth, MeasureSpec.EXACTLY), 
                MeasureSpec.makeMeasureSpec(finalHeight, MeasureSpec.EXACTLY));
    }
}