android通过代码控制ListView上下滚动

本文详述了如何在Android应用中通过编程方式实现ListView的上下滚动功能,结合示例代码展示了按下按钮触发ListView滚动的实现过程。

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本文将介绍一种通过代码控制ListView上下滚动的方法。

先上图:

截图1

按下按钮会触发ListView滚动或停止。


实现该功能并不难,下面给出主要代码MainActivity.java

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);
		}
	};
}

实现ListView位置变动的是smoothScrollBy方法。

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.  

工程源码:

Android listview 代码控制上下移动



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