FlowLayout

FlowLayout.java

package jp.cyberagent.android.base.ui.widget;

import java.util.ArrayList;
import java.util.List;

import android.content.Context;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewGroup;

/**
 * @author RAW
 */
public class FlowLayout extends ViewGroup {

    private final List<Integer> mLineHeights = new ArrayList<Integer>();

    public static class LayoutParams extends ViewGroup.MarginLayoutParams {

        public final int horizontalSpacing;
        public final int verticalSpacing;

        /**
         * @param horizontalSpacing Pixels between items, horizontally
         * @param verticalSpacing Pixels between items, vertically
         */
        public LayoutParams(final int horizontalSpacing, final int verticalSpacing) {
            super(0, 0);
            this.horizontalSpacing = horizontalSpacing;
            this.verticalSpacing = verticalSpacing;
        }
    }

    public FlowLayout(final Context context) {
        super(context);
    }

    public FlowLayout(final Context context, final AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    protected void onMeasure(final int widthMeasureSpec, final int heightMeasureSpec) {
        assert (MeasureSpec.getMode(widthMeasureSpec) != MeasureSpec.UNSPECIFIED);

        final int maxWidth = MeasureSpec.getSize(widthMeasureSpec) - getPaddingLeft()
                - getPaddingRight();
        int width = 0;
        int height = MeasureSpec.getSize(heightMeasureSpec) - getPaddingTop() - getPaddingBottom();
        final int count = getChildCount();
        int currentLineHeight = 0;
        int currentHeight = 0;
        mLineHeights.clear();

        int xpos = getPaddingLeft();
        int ypos = getPaddingTop();

        int childHeightMeasureSpec;
        if (MeasureSpec.getMode(heightMeasureSpec) == MeasureSpec.AT_MOST) {
            childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(height, MeasureSpec.AT_MOST);
        } else {
            childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED);
        }

        for (int i = 0; i < count; i++) {
            final View child = getChildAt(i);
            if (child.getVisibility() != GONE) {
                final LayoutParams lp = (LayoutParams) child.getLayoutParams();
                child.measure(MeasureSpec.makeMeasureSpec(maxWidth, MeasureSpec.AT_MOST),
                        childHeightMeasureSpec);
                final int childw = child.getMeasuredWidth();
                currentHeight = Math
                        .max(currentLineHeight, child.getMeasuredHeight() + lp.verticalSpacing);

                if (xpos + childw > maxWidth) {
                    xpos = getPaddingLeft();
                    ypos += currentLineHeight;
                    mLineHeights.add(currentLineHeight);
                    currentLineHeight = currentHeight;
                } else {
                    width = Math.max(xpos + childw, width);
                    currentLineHeight = currentHeight;
                }

                xpos += childw + lp.horizontalSpacing;
            }
        }
        mLineHeights.add(currentHeight);

        if (MeasureSpec.getMode(heightMeasureSpec) == MeasureSpec.UNSPECIFIED) {
            height = ypos + currentLineHeight;
        } else if (MeasureSpec.getMode(heightMeasureSpec) == MeasureSpec.AT_MOST) {
            if (ypos + currentLineHeight < height) {
                height = ypos + currentLineHeight;
            }
        }

        if (MeasureSpec.getMode(widthMeasureSpec) == MeasureSpec.EXACTLY) {
            width = maxWidth;
        }

        setMeasuredDimension(width, height);
    }

    @Override
    protected ViewGroup.LayoutParams generateDefaultLayoutParams() {
        return new LayoutParams(1, 1); // default of 1px spacing
    }

    @Override
    protected boolean checkLayoutParams(final ViewGroup.LayoutParams p) {
        if (p instanceof LayoutParams) {
            return true;
        }
        return false;
    }

    @Override
    protected void onLayout(final boolean changed, final int l, final int t, final int r,
            final int b) {
        final int count = getChildCount();
        final int width = r - l;
        int xpos = getPaddingLeft();
        int ypos = getPaddingTop();
        int currentLine = 0;

        for (int i = 0; i < count; i++) {
            final View child = getChildAt(i);
            if (child.getVisibility() != GONE) {
                final int childw = child.getMeasuredWidth();
                final int childh = child.getMeasuredHeight();
                final LayoutParams lp = (LayoutParams) child.getLayoutParams();
                if (xpos + childw > width) {
                    xpos = getPaddingLeft();
                    ypos += mLineHeights.get(currentLine++);
                }
                child.layout(xpos, ypos, xpos + childw, ypos + childh);
                xpos += childw + lp.horizontalSpacing;
            }
        }
    }
}

how to use this layout file in my xml layout file?
Using the code below is giving me error

<com.example.ja.slidingwindow.FlowLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/main_relative_layout"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="abc"/>
</com.example.ja.slidingwindow.FlowLayout>