我基本上是在尝试从另一个类中的 sqlite db 获取信息。我在 onCreate 方法中没有任何问题,但是当我尝试在 onCreate 内部的 onClickListener 中使用它时,我找不到要使用的正确上下文。我的代码如下:
private AutoCompleteTextView search;
private Button showInfoButton;
private TextView courseInfo;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main_courses);
final Context baseContext = getBaseContext();
courseInfo = (TextView) this.findViewById(R.id.text);
DataBase db = new DataBase(this.getApplicationContext());
db.openDataBase();
final ArrayList<String> aCourses = db.getCoursesArr();
db.close();
search = (AutoCompleteTextView) findViewById(R.id.autocomplete_course);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, R.layout.list_courses, aCourses);
search.setAdapter(adapter);
showInfoButton = (Button) this.findViewById(R.id.show_info_button);
showInfoButton.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
if (aCourses.toString().contains(search.getText()) == false ) {
courseInfo.setText("Please select a course from the drop-down menu and click on the \"Show course information\" button");
}
else{
String selectedCourse = search.toString();
DataBase db1 = new DataBase(baseContext);
db1.openDataBase();
ArrayList<String> courseAttributes = db1.getCourseAttributes();
ArrayList<String> attributeValues = db1.getAttributeValues(selectedCourse);
db1.close();
String courseInformation = "";
for (int i=0; i < courseAttributes.size(); i++){
courseInformation = courseInformation + courseAttributes.get(i) + ": " + attributeValues.get(i) + System.getProperty("line.separator");
}
courseInfo.setText(courseInformation);
}
}
});
}
问题随之而来
DataBase db1 = new DataBase(baseContext);
我试过把它改成
DataBase db = new DataBase(this.getApplicationContext());
和
DataBase db = new DataBase(null);
并且我尝试的每一种方式,程序都会运行,但是当它出现在 else 情况下时,它会抛出一个错误并关闭。谁能告诉我应该使用什么上下文才能使其运行?