AutoGridView.java

package nl.obduro.views;

import android.content.Context;
import android.content.res.Configuration;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;
import android.widget.GridView;
import android.widget.ListAdapter;

/**
 * Automatically calculates the ideal for each row
 * @author JJ
 *
 */
public class AutoGridView extends GridView {

	private static final String TAG = "AutoGridView";
	private int numColumnsID;
	private int previousFirstVisible;
	private int numColumns = 1;
	
	public AutoGridView(Context context, AttributeSet attrs, int defStyle) {
		super(context, attrs, defStyle);
		init(attrs);
	}
	
	public AutoGridView(Context context, AttributeSet attrs) {
		super(context, attrs);
		init(attrs);
	}
	
	public AutoGridView(Context context) {
		super(context);
	}
	
	/**
	 * Sets the numColumns based on the attributeset
	 */
	private void init(AttributeSet attrs) {
		// Read numColumns out of the AttributeSet
		int count = attrs.getAttributeCount();
		if(count > 0) {
			for(int i = 0; i < count; i++) {
				String name = attrs.getAttributeName(i);
				if(name != null && name.equals("numColumns")) {
					// Update columns
					this.numColumnsID = attrs.getAttributeResourceValue(i, 1);
					updateColumns();
					break;
				}
			}
		}
		Log.d(TAG, "numColumns set to: " + numColumns);
	}

	
	/**
	 * Reads the amount of columns from the resource file and
	 * updates the "numColumns" variable
	 */
	private void updateColumns() {
		this.numColumns = getContext().getResources().getInteger(numColumnsID);
	}
	
	@Override
	public void setNumColumns(int numColumns) {
		this.numColumns = numColumns;
		super.setNumColumns(numColumns);
	
		Log.d(TAG, "setSelection --> " + previousFirstVisible);
		setSelection(previousFirstVisible);
	}
	
	@Override
	protected void onLayout(boolean changed, int leftPos, int topPos, int rightPos, int bottomPos) {
		super.onLayout(changed, leftPos, topPos, rightPos, bottomPos);
		setHeights();
	}
	
	@Override
	protected void onConfigurationChanged(Configuration newConfig) {
		updateColumns();
		setNumColumns(this.numColumns);
	}
	
	@Override
	protected void onScrollChanged(int newHorizontal, int newVertical, int oldHorizontal, int oldVertical) {
		// Check if the first visible position has changed due to this scroll
		int firstVisible = getFirstVisiblePosition();
		if(previousFirstVisible != firstVisible) {
			// Update position, and update heights
			previousFirstVisible = firstVisible;
			setHeights();
		}
		
		super.onScrollChanged(newHorizontal, newVertical, oldHorizontal, oldVertical);
	}
	
	/**
	 * Sets the height of each view in a row equal to the height of the tallest view in this row.
	 * @param firstVisible The first visible position (adapter order)
	 */
	private void setHeights() {
		ListAdapter adapter = getAdapter();
		
		if(adapter != null) {
			for(int i = 0; i < getChildCount(); i+=numColumns) {
				// Determine the maximum height for this row
				int maxHeight = 0;
				for(int j = i; j < i+numColumns; j++) {
					View view = getChildAt(j);
					if(view != null && view.getHeight() > maxHeight) {
						maxHeight = view.getHeight();
					}
				}
				//Log.d(TAG, "Max height for row #" + i/numColumns + ": " + maxHeight);
				
				// Set max height for each element in this row
				if(maxHeight > 0) {
					for(int j = i; j < i+numColumns; j++) {
						View view = getChildAt(j);
						if(view != null && view.getHeight() != maxHeight) {
							view.setMinimumHeight(maxHeight);
						}
					}
				}
			}
		}
	}
	

}