windows phone LongListSelector加载下一页

LongListSelector利用ListHeader、ListFooter加载上一页和下一页XAML代码：

<phone:LongListSelector>
<phone:LongListSelector.ListHeader>
    <Grid>
        <Button Content="加载上一页" Click="pre_Click"/>
    </Grid>
</phone:LongListSelector.ListHeader>
<phone:LongListSelector.ListFooter >
    <Grid>
        <Button Content="加载下一页" Click="next_Click"/>
    </Grid>
</phone:LongListSelector.ListFooter>
</phone:LongListSelector>

具体实现过程就不写了