在ListView的整个列表中,设置当前组件显示的第几项,或者理解成定位到列表中具体的某一项时,使用ListView类中的方法:
@Override public void setSelection(int position) { setSelectionFromTop(position, 0); }
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参数position即指定显示列表中具体的某一项子项,position的取值为大于等于0,如需要指定显示列表中的第N项时,position = N - 1;在下面的例子中,默认显示了列表中的第5项,关键代码为:
效果图:
此时,在界面的顶端(ListView组件的顶部)直接显示第5项子项。
当前显示界面代码:
package net.oschina.git.zhaikun.androiddeveloped.activitys;
import android.os.Bundle; import android.support.annotation.Nullable; import android.support.v7.app.AppCompatActivity; import android.widget.ListView;
import net.oschina.git.zhaikun.androiddeveloped.R; import net.oschina.git.zhaikun.androiddeveloped.adapter.ListViewDemoAdapter;
import java.util.ArrayList; import java.util.List;
/** * Created by zhaikun68 on 2018/3/5. * <p> * ListView演示Demo */ public class ListViewDemoActivity extends AppCompatActivity {
private ListView testLv;//ListView组件 private List<String> dataList = new ArrayList<>();//存储数据
@Override protected void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_listview_demo);
init();//初始化数据及视图 }
/** * 初始化数据及视图 */ private void init() { testLv = (ListView) findViewById(R.id.test_lv);
//初始化10项数据 for (int i = 1; i <= 20; i++) { dataList.add("显示内容" + i); }
//设置ListView的适配器 testLv.setAdapter(new ListViewDemoAdapter(this, dataList)); testLv.setSelection(4); } }
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当前显示界面的布局文件:
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical">
<ListView android:id="@+id/test_lv" android:layout_width="match_parent" android:layout_height="match_parent" android:divider="@color/colorPrimaryDark" android:dividerHeight="3dp" android:listSelector="#ff0000" android:scrollbars="none"/> </LinearLayout>
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适配器代码:
package net.oschina.git.zhaikun.androiddeveloped.adapter;
import android.content.Context; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.BaseAdapter; import android.widget.ImageView; import android.widget.TextView;
import net.oschina.git.zhaikun.androiddeveloped.R;
import java.util.List;
/** * Created by zhaikun68 on 2018/3/5. * <p> * ListView演示Demo中的数据适配器 */ public class ListViewDemoAdapter extends BaseAdapter {
private Context context;//上下文对象 private List<String> dataList;//ListView显示的数据
/** * 构造器 * * @param context 上下文对象 * @param dataList 数据 */ public ListViewDemoAdapter(Context context, List<String> dataList) { this.context = context; this.dataList = dataList; }
@Override public int getCount() { return dataList == null ? 0 : dataList.size(); }
@Override public Object getItem(int position) { return dataList.get(position); }
@Override public long getItemId(int position) { return position; }
@Override public View getView(int position, View convertView, ViewGroup parent) { ViewHolder viewHolder; //判断是否有缓存 if (convertView == null) { convertView = LayoutInflater.from(context).inflate(R.layout.item_listview_demo, null); viewHolder = new ViewHolder(convertView); convertView.setTag(viewHolder); } else { //得到缓存的布局 viewHolder = (ViewHolder) convertView.getTag(); }
//设置图片 viewHolder.pictureImg.setImageResource(R.mipmap.ic_launcher); //设置内容 viewHolder.contentTv.setText(dataList.get(position));
return convertView; }
/** * ViewHolder类 */ private final class ViewHolder {
ImageView pictureImg;//图片 TextView contentTv;//内容
/** * 构造器 * * @param view 视图组件(ListView的子项视图) */ ViewHolder(View view) { pictureImg = (ImageView) view.findViewById(R.id.picture_img); contentTv = (TextView) view.findViewById(R.id.content_tv); } } }
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列表子项的布局文件:
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="horizontal" android:padding="5dp">
<ImageView android:id="@+id/picture_img" android:layout_width="30dp" android:layout_height="30dp" android:layout_marginRight="5dp" android:src="@mipmap/ic_launcher"/>
<TextView android:id="@+id/content_tv" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_gravity="center_vertical" android:text="显示内容"/> </LinearLayout>
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