如何使 ListView 仅显示最后 6 个项目？

Question

我的 Activity 只显示 listview（他从 SQLite 数据库中提取数据），他可以显示的数据没有限制，而且效果很好。

现在，我想向 MainActivity 添加一个新的小列表视图，它将仅显示最后五个数据。

我在网络上的任何地方都找不到怎么做..

DataListActivity.java

   package com.example.ido.grades;
    import android.content.Intent;
    import android.database.Cursor;
    import android.database.sqlite.SQLiteDatabase;
    import android.support.v7.app.ActionBarActivity;
    import android.os.Bundle;
    import android.view.ContextMenu;
    import android.view.MenuInflater;
    import android.view.MenuItem;
    import android.view.View;
    import android.widget.AdapterView;
    import android.widget.ListView;
    import android.widget.Toast;
    public class DataListActivity extends ActionBarActivity {
        ListView listView;
        SQLiteDatabase sqLiteDatabase;
        CourseDbHelper courseDbHelper;
        Cursor cursor;
        ListDataAdaptar listDataAdaptar;
        @Override
        protected void onCreate(Bundle savedInstanceState) {

            super.onCreate(savedInstanceState);
            setContentView(R.layout.update_course);
            hideActionBar();
            listView = (ListView) findViewById(R.id.list_view);
            listDataAdaptar = new ListDataAdaptar(getApplicationContext(),R.layout.row_layout);
            listView.setAdapter(listDataAdaptar);
            registerForContextMenu(listView);
            courseDbHelper = new CourseDbHelper(getApplicationContext());
            sqLiteDatabase = courseDbHelper.getReadableDatabase();
            cursor = courseDbHelper.getInformation(sqLiteDatabase);
            registerForContextMenu(listView);
            if (!cursor.moveToFirst()){
            }
            else {
                do {
                    String year,semester,course,points,grade;
                    year = cursor.getString(0);
                    semester = cursor.getString(1);
                    course = cursor.getString(2);
                    points = cursor.getString(3);
                    grade = cursor.getString(4);
                    DataProvider dataProvider  = new DataProvider(year,semester,course,points,grade);
                    listDataAdaptar.add(dataProvider);
                }
                while (cursor.moveToNext());
            }
        }
        public void onCreateContextMenu(ContextMenu menu, View v, ContextMenu.ContextMenuInfo menuInfo) {
            MenuInflater inflater = getMenuInflater();
            inflater.inflate(R.menu.menu_data_list, menu);

        }
        public boolean onContextItemSelected(MenuItem item) {
            AdapterView.AdapterContextMenuInfo info =
                    (AdapterView.AdapterContextMenuInfo) item.getMenuInfo();
            int mySelectedRowIndex = info.position;
            switch (item.getItemId()) {
                case R.id.update_item:
                    courseDbHelper = new CourseDbHelper(getApplicationContext());
                    sqLiteDatabase = courseDbHelper.getReadableDatabase();
                    DataProvider raw2 = (DataProvider)listDataAdaptar.getItem(mySelectedRowIndex);

                    Intent i = new Intent(DataListActivity.this, UpdateCourseActivity.class);
                    String year = raw2.getYear();
                    String semester = raw2.getSemester();
                    String course =  raw2.getCourse();
                    String points =  raw2.getPoints();
                    String grade =  raw2.getGrade();
                    int semIndex;
                    if (semester.equals("A'")){
                        semIndex =1;
                    }
                    else if (semester.equals("B'")){
                        semIndex =2;
                    }
                    else{
                        semIndex=3;
                    }
                    i.putExtra("YEAR", year);
                    i.putExtra("SEMESTER", Integer.toString(semIndex));
                    i.putExtra("COURSE", course);
                    i.putExtra("POINTS", points);
                    i.putExtra("GRADE", grade);
                    i.putExtra("POS", Integer.toString(mySelectedRowIndex));

                    startActivity(i);


                    return true;
                case R.id.delete_item:
                    courseDbHelper = new CourseDbHelper(getApplicationContext());
                    sqLiteDatabase = courseDbHelper.getReadableDatabase();
                    DataProvider raw = (DataProvider)listDataAdaptar.getItem(mySelectedRowIndex);
                    courseDbHelper.deleteInformation(raw.getYear(), raw.getSemester(), raw.getCourse(), raw.getPoints(), raw.getGrade());
                    Toast.makeText(this,"delete, pos["+mySelectedRowIndex+"]",Toast.LENGTH_LONG).show();
                    finish();
                    startActivity(getIntent());
                    return true;
                default:
                    return super.onOptionsItemSelected(item);
            }
        }
        public void onBackPressed() {
            startActivity(new Intent(this, MainActivity.class));
        }


        private void hideActionBar() {
            //Hide the action bar only if it exists
            if (getSupportActionBar() != null) {
                getSupportActionBar().hide();
            }
        }
        }

ListDataAdapter.java

package com.example.ido.grades;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;

/**
 * Created by Ido on 08/08/2015.
 */
public class ListDataAdaptar extends ArrayAdapter{
        List list = new ArrayList();
    public ListDataAdaptar(Context context, int resource) {
        super(context, resource);
    }

    static class LayoutHandler{
        TextView YEAR,SEMESTER,COURSE,POINTS,GRADE;
    }
    @Override
    public void add(Object object) {
        super.add(object);
        list.add(object);
    }


    @Override
    public int getCount() {
        return list.size();
    }

    @Override
    public Object getItem(int position) {
        return list.get(position);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View row = convertView;
        LayoutHandler layoutHandler;
        if (row == null){
            LayoutInflater layoutInflater = (LayoutInflater) this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            row  = layoutInflater.inflate(R.layout.row_layout,parent,false);
            layoutHandler = new LayoutHandler();
            layoutHandler.YEAR = (TextView)row.findViewById(R.id.textYear);
            layoutHandler.SEMESTER = (TextView)row.findViewById(R.id.textSemester);
            layoutHandler.COURSE = (TextView)row.findViewById(R.id.textCourse);
            layoutHandler.POINTS = (TextView)row.findViewById(R.id.textPoints);
            layoutHandler.GRADE = (TextView)row.findViewById(R.id.textGrade);
            row.setTag(layoutHandler);
        }
        else{
            layoutHandler = (LayoutHandler) row.getTag();

        }
        DataProvider dataProvider = (DataProvider) this.getItem(position);
        layoutHandler.YEAR.setText(dataProvider.getYear());
        layoutHandler.SEMESTER.setText(dataProvider.getSemester());
        layoutHandler.COURSE.setText(dataProvider.getCourse());
        layoutHandler.POINTS.setText(dataProvider.getPoints());
        layoutHandler.GRADE.setText(dataProvider.getGrade());
        return row;
    }
}

Answer 1

忽略您的代码，您显然将一个对象数组传递到您的数组适配器的构造函数中。

Object[] data = new Object[]{...}
MyArrayAdapter myAdapter = new MyArrayAdapter(data ,... else)

您只需获取此 data 数组并将最后 6 个元素附加到新数组即可。

Object[] data2 = new Object[6]
for(int i = data.length()-7; i<data.length(); i++){
    data2[data.length()-i] = data[i]

然后创建一个新的适配器，传递新的data2 数组。

MyArrayAdapter myAdapter = new MyArrayAdapter(data2, ... else)

Answer 2

创建将返回最后 6 行 i 游标 [SQL 查询] 的方法。

cursor = courseDbHelper.getInformationLast_6(sqLiteDatabase);

SQL：

 SELECT * FROM table ORDER BY column DESC [ASC] LIMIT 6;

Answer 3

通过这个，您可以在您的列表中获得 6 个项目。尝试在您的适配器类中使用以下代码。

public int getCount() {
        return 6;
    }

比按升序或降序将您的查询限制为 6。

Answer 4

您可以移动到当前光标的最后一个位置并移动到前面的行以获取所需的数据。排序：

ArrayList string;
if (cursor.moveToLast()){
   for (int i = 1; i<=6; i++) {
   string.add(cursor.getString(cursor.getColumnIndex("your_data")));
   cursor.moveToPrevious();
   } 
}
cursor.close();

结果将是 ArrayList，其中包含光标数据的最后 6 个字符串。您可以将其提供给新的 ArrayAdapter 并将其显示在屏幕上。

除了 ArrayList，您还可以使用所有现有数据创建另一个游标，并将其提供给已经存在的适配器，例如，如下所述： https://stackoverflow.com/a/18290921/4890659