请大家帮个忙,同时读写文件问题

private void button1_click（object sender, eventargs e)
{
    filestream vfilestream = new filestream（@"c:\temp\temp.txt",
        filemode.open, fileaccess.read, fileshare.readwrite);
    streamreader vstreamreader = new streamreader（vfilestream, encoding.default);
    console.writeline（vstreamreader.readtoend（));
}
private filestream writestream = new filestream（@"c:\temp\temp.txt",
    filemode.append, fileaccess.write, fileshare.readwrite);

private streamwriter streamwriter;
private void button2_click（object sender, eventargs e)
{                    
    if （streamwriter == null)
        streamwriter = new streamwriter（writestream, encoding.default);
    streamwriter.writeline（"zswang路过");
    streamwriter.flush（);
}