项目中有一个需求
用户点击某一个按钮,listview滚动到指定的位置的item,需要的效果是平滑的滑动
研究了一下listview,在真机和模拟器上都试了一下(小米4,系统为6.0)模拟器系统为(4.0.3)
代码如下
package org.dengzh;
import java.util.ArrayList;
import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.animation.Animation;
import android.view.animation.AnimationUtils;
import android.widget.AbsListView;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.ListAdapter;
import android.widget.ListView;
/**
*
* @author dengzh
*
*/
public class MainActivity extends Activity implements View.OnClickListener {
private ListView lv;
private ImageView iv_back_top;
private ArrayList<String> list = new ArrayList<String>();
//private boolean isBackTop = false;
private Animation fadeInAnim;
private Animation fadeOutAnim;
private Button position_1, position_2, position_3;
//记录当前要滚动的目标位置
private int curScrollToPosition = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
init();
}
private void init() {
fadeInAnim = AnimationUtils.loadAnimation(this, R.anim.anim_fade_in);
fadeInAnim.setFillAfter(true);
fadeOutAnim = AnimationUtils.loadAnimation(this, R.anim.anim_fade_out);
fadeOutAnim.setFillAfter(true);
position_1 = (Button) findViewById(R.id.position_1);
position_2 = (Button) findViewById(R.id.position_2);
position_3 = (Button) findViewById(R.id.position_3);
lv = (ListView) findViewById(R.id.lv);
iv_back_top = (ImageView) findViewById(R.id.iv_back_top);
for (int i = 0; i < 999; i++) {
list.add(i + "");
}
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, list);
lv.setAdapter(adapter);
lv.setOnScrollListener(new AbsListView.OnScrollListener() {
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
//处理滚动条滚动停止时
if (scrollState == SCROLL_STATE_IDLE) {
Log.d("android", "SCROLL_STATE_IDLE");
//判断是否滚动到了第0项,如果是,就隐藏 右下角的 图标,
//如果不是,那么显示
if (lv.getFirstVisiblePosition() == 0) {
if (iv_back_top.getVisibility() == View.VISIBLE) {
iv_back_top.startAnimation(fadeOutAnim);
iv_back_top.setVisibility(View.GONE);
}
} else {
if (iv_back_top.getVisibility() == View.GONE) {
iv_back_top.setVisibility(View.VISIBLE);
iv_back_top.startAnimation(fadeInAnim);
}
}
//如果当前滚动的目标位置不为-1,也就是说这是由点击按钮触发的自动滚动,
//那么最后定位到对应的curScrollPosition
if (curScrollToPosition != -1) {
lv.setSelection(curScrollToPosition);
}
//最后把curScrollToPosition置为-1, 这样不这样做,那么当自动定位结束后,
//再去用手指滑动listview,当滑动结束后,listview在这里仍然会自动定位到上一个curScrollPosition去
curScrollToPosition = -1;
}
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
}
});
lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,
long arg3) {
Log.d("android", arg3 + "");
}
});
iv_back_top.setOnClickListener(this);
position_1.setOnClickListener(this);
position_2.setOnClickListener(this);
position_3.setOnClickListener(this);
}
@Override
public void onClick(View v) {
int position = 0;
switch (v.getId()) {
case R.id.iv_back_top:
//返回顶端
//smoothScrollToPositionFromTop我在手机(小米4)和模拟器(4.0.3)上测了很久
//手机上完全没有问题,但是模拟器上的话,如果position的位置很大,比较要滚动到900,那么有时候会滚动到一半停止了,并没有最终滚动到900的位置
//所以这里用curScrollPosition保存了滚动的目标位置,在onScrollStateChanged监听中,当滚动样状态为停止时,再调用lv.setSelection(curScrollToPosition)来最终再一次将listview的位置定位到目标位置
//smoothScrollToPositionFromTop中的第二个参数,我看文档中的意思为Desired distance in pixels of position from the top of the view when scrolling is finished
//理解为当滚动停止时,当前定位的这个item,距离top的距离是多少,我在这儿设置为0
lv.smoothScrollToPositionFromTop(0, 0, 5000);
break;
case R.id.position_1:
position = Integer.parseInt(position_1.getTag().toString());
curScrollToPosition = position;
lv.smoothScrollToPositionFromTop(position, 0, 5000);
break;
case R.id.position_2:
position = Integer.parseInt(position_2.getTag().toString());
curScrollToPosition = position;
lv.smoothScrollToPositionFromTop(position, 0, 5000);
break;
case R.id.position_3:
position = Integer.parseInt(position_3.getTag().toString());
curScrollToPosition = position;
lv.smoothScrollToPositionFromTop(position, 0, 5000);
break;
}
}
}
smoothScrollToPositionFromTop我在手机(小米4)和模拟器(4.0.3)上测了很久
手机上完全没有问题,但是模拟器上的话,如果position的位置很大,比较要滚动到900,那么有时候会滚动到一半停止了,并没有最终滚动到900的位置
所以这里用curScrollPosition保存了滚动的目标位置,在onScrollStateChanged监听中,当滚动样状态为停止时,再调用lv.setSelection(curScrollToPosition)来最终再一次将listview的位置定位到目标位置
smoothScrollToPositionFromTop中的第二个参数,我看文档中的意思为Desired distance in pixels of position from the top of the view when scrolling is finished
理解为当滚动停止时,当前定位的这个item,距离top的距离是多少,我在这儿设置为0
效果图如下