自定义挤压头部的listview

package com.handcar.view;

import android.content.Context;
import android.graphics.Canvas;
import android.util.AttributeSet;
import android.view.View;
import android.widget.ListAdapter;
import android.widget.ListView;

/**
* 自定义挤压头部的listview
*
* @author blue
*
*/
public class PinnedHeaderListView extends ListView
{

public interface PinnedHeaderAdapter
{
public static final int PINNED_HEADER_GONE = 0;
public static final int PINNED_HEADER_VISIBLE = 1;
public static final int PINNED_HEADER_PUSHED_UP = 2;

int getPinnedHeaderState(int position);

void configurePinnedHeader(View header, int position, int alpha);
}

private static final int MAX_ALPHA = 255;

private PinnedHeaderAdapter mAdapter;
private View mHeaderView;
private boolean mHeaderViewVisible;
private int mHeaderViewWidth;
private int mHeaderViewHeight;

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

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

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

protected void onLayout(boolean changed, int left, int top, int right, int bottom)
{
super.onLayout(changed, left, top, right, bottom);
if (mHeaderView != null)
{
mHeaderView.layout(0, 0, mHeaderViewWidth, mHeaderViewHeight);
configureHeaderView(getFirstVisiblePosition());
}
}

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
{
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
if (mHeaderView != null)
{
measureChild(mHeaderView, widthMeasureSpec, heightMeasureSpec);
mHeaderViewWidth = mHeaderView.getMeasuredWidth();
mHeaderViewHeight = mHeaderView.getMeasuredHeight();
}
}

public void setPinnedHeaderView(View view)
{
mHeaderView = view;
if (mHeaderView != null)
{
setFadingEdgeLength(0);
}
requestLayout();
}

public void setAdapter(ListAdapter adapter)
{
super.setAdapter(adapter);
mAdapter = (PinnedHeaderAdapter) adapter;
}

public void configureHeaderView(int position)
{
if (mHeaderView == null)
{
return;
}
int state = mAdapter.getPinnedHeaderState(position);
switch (state)
{
case PinnedHeaderAdapter.PINNED_HEADER_GONE:
{
mHeaderViewVisible = false;
break;
}

case PinnedHeaderAdapter.PINNED_HEADER_VISIBLE:
{
mAdapter.configurePinnedHeader(mHeaderView, position, MAX_ALPHA);
if (mHeaderView.getTop() != 0)
{
mHeaderView.layout(0, 0, mHeaderViewWidth, mHeaderViewHeight);
}
mHeaderViewVisible = true;
break;
}

case PinnedHeaderAdapter.PINNED_HEADER_PUSHED_UP:
{
View firstView = getChildAt(0);
if(firstView == null){
return;
}
int bottom = firstView.getBottom();
int headerHeight = mHeaderView.getHeight();
int y;
int alpha;
if (bottom < headerHeight)
{
y = (bottom - headerHeight);
alpha = MAX_ALPHA * (headerHeight + y) / headerHeight;
} else
{
y = 0;
alpha = MAX_ALPHA;
}
mAdapter.configurePinnedHeader(mHeaderView, position, alpha);
if (mHeaderView.getTop() != y)
{
mHeaderView.layout(0, y, mHeaderViewWidth, mHeaderViewHeight + y);
}
mHeaderViewVisible = true;
break;
}
}
}

protected void dispatchDraw(Canvas canvas)
{
super.dispatchDraw(canvas);
if (mHeaderViewVisible)
{
drawChild(canvas, mHeaderView, getDrawingTime());
}
}
}