我正在开发一个示例应用程序来学习 android。它应该显示一个多选列表，当用户单击按钮时，它应该显示在顶部的 TextView 中选择的项目。似乎当我尝试从 ListView 检索所选项目时，总是返回一个空数组。谁能向我解释为什么会这样以及我缺少什么才能使其正常工作？（仅供参考，代码是格兰特艾伦从 Android 4 开始的修改程序）
这是布局xml文件：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
<TextView
android:id="@+id/selection"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
<Button
android:id="@+id/getSelections"
android:text="Show Selections"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="listSelected" />
<ListView
android:id="@android:id/list"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:drawSelectorOnTop="false"
android:choiceMode="multipleChoice" />
</LinearLayout>
这是相关的Java：
package com.commonsware.android.checklist;
import android.os.Bundle;
import android.app.ListActivity;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.view.*;
public class ChecklistDemo extends ListActivity {
private static final String[] items={"lorem", "ipsum", "dolor",
"sit", "amet",
"consectetuer", "adipiscing", "elit", "morbi", "vel",
"ligula", "vitae", "arcu", "aliquet", "mollis",
"etiam", "vel", "erat", "placerat", "ante",
"porttitor", "sodales", "pellentesque", "augue", "purus"};
private TextView selection;
@Override
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
setContentView(R.layout.main);
setListAdapter(new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_multiple_choice,
items));
selection = (TextView)findViewById(R.id.selection);
}
public void listSelected(View view) {
long[] chosenOnes = getListView().getCheckedItemIds();
selection.setText("Items selected: ");
selection.setText(Integer.toString(chosenOnes.length));
for (long x:chosenOnes) {
int i = Long.valueOf(x).intValue();
selection.setText(selection.getText() + ", " + items[i]);
}
}
}