Android通过代码控制ListView上下滚动的方法

package cn.guet.levide;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ListView;
public class MainActivity extends Activity implements OnClickListener {
 private Button btn_up, btn_down, btn_stop; // 三个按钮
 private ListView listview;
 private Adapter adapter;
 @Override
 public void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.main);
 findBy();
 init();
 }
 private void init() {
 btn_up.setOnClickListener(this);
 btn_down.setOnClickListener(this);
 btn_stop.setOnClickListener(this);
 adapter = new Adapter(this);
 listview.setAdapter(adapter);
 }
 private void findBy() {
 btn_up = (Button) findViewById(R.id.btn_scroll_up);
 btn_down = (Button) findViewById(R.id.btn_scroll_down);
 btn_stop = (Button) findViewById(R.id.btn_scroll_stop);
 listview = (ListView) findViewById(R.id.listview);
 }
 @Override
 public void onClick(View v) {
 switch (v.getId()) {
 case R.id.btn_scroll_down:
  listScrollDown();
  break;
 case R.id.btn_scroll_up:
  listScrollUp();
  break;
 case R.id.btn_scroll_stop:
  listScrollOff();
  break;
 }
 }
 Handler handler = new Handler() {
 @Override
 public void handleMessage(Message msg) {
  handler.removeCallbacks(run_scroll_down);
  handler.removeCallbacks(run_scroll_up);
 }
 };
 /**
 * 向上滚动
 */
 public void listScrollUp() {
 listScrollOff();
 handler.postDelayed(run_scroll_up, 0);
 }
 /**
 * 向下滚动
 */
 public void listScrollDown() {
 listScrollOff();
 handler.postDelayed(run_scroll_down, 0);
 }
 /**
 * 停止滚动
 */
 public void listScrollOff() {
 handler.removeCallbacks(run_scroll_down);
 handler.removeCallbacks(run_scroll_up);
 }
 Runnable run_scroll_up = new Runnable() {
 @Override
 public void run() {
  /**
  * public void smoothScrollBy (int distance, int duration) 
  * 
  * Added in API level 8 Smoothly scroll by distance pixels over duration milliseconds.
  * 
  * Parameters 
  *   distance Distance to scroll in pixels.
  *   duration Duration of the scroll animation in milliseconds.
  */
  listview.smoothScrollBy(1, 10);
  handler.postDelayed(run_scroll_up, 10);
 }
 };
 Runnable run_scroll_down = new Runnable() {
 @Override
 public void run() {
  listview.smoothScrollBy(-1, 10);
  handler.postDelayed(run_scroll_down, 10);
 }
 };
}

public void smoothScrollBy (int distance, int duration)
  Smoothly scroll by distance pixels over duration milliseconds.

Parameters
  distance Distance to scroll in pixels.
  duration Duration of the scroll animation in milliseconds.