Question

我对Android开发很新，而且我的Java有点生疏，所以请耐心等待。我想完成以下任务：

启动应用程序后，所有用户的课程和信息将填充在主要活动中，并且将显示添加新课程的按钮选项。最初在添加之前不会显示任何课程。
单击添加课程将显示新活动，并在保存数据输入时将新的课程记录插入到数据库中。控制将返回到主活动，其中列表视图将使用新添加的课程进行刷新。以下是我正在使用的4个类和两个布局。

问题：此时我没有成功确认已插入数据并将数据拉回并在屏幕上显示。我想我已经确定了一个问题，即course_list没有填充课程，但由于我没有收到任何错误，我正在努力找出真正的问题。任何见解或指导都会非常感激！

MainActivity.Java

import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;

import java.util.ArrayList;


public class MainActivity extends ActionBarActivity {
    private ListView courseListView;

    private ArrayList<Course> course_list = new ArrayList<Course>();
    private ArrayList<String> course_names = new ArrayList<String>();
    private ArrayAdapter<String> ap;
    DatabaseHelper db;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        courseListView = (ListView) findViewById(R.id.course_list);

        // Init database
        db = new DatabaseHelper(getApplicationContext());
        db.getWritableDatabase();
        initAdapter();
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    // Called when Add Course button is pressed
    public void onClick( View v ) {
        Intent intent = new Intent(v.getContext(), AddCourseActivity.class);
        v.getContext().startActivity(intent);
    }

    //
    private void initAdapter() {
        if( course_list.size() != 0) {
            course_list.clear();
            course_list = db.getCourses();

            for (int i = 0; i < course_list.size(); ++i) {
                course_names.add(course_list.get(i).getCourseName());
            }
            ap = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, course_names);

            courseListView.setAdapter(ap);
        }
    }
}

DatabaseHelper.java

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import java.util.ArrayList;

public class DatabaseHelper extends SQLiteOpenHelper{
    public static final String DATABASE_NAME = "Courses";
    public static final String COURSE_TABLE = "MyCourses";
    public static final String KEY_COURSE_NUM = "CourseNum";
    public static final String KEY_COURSE_NAME = "CourseName";
    public static final String KEY_COURSE_DESC = "CourseDesc";
    public static final String KEY_DATE = "Date";
    public static final String KEY_TIME = "Time";
    public static final String KEY_INSTRUCTOR = "Instructor";
    private ArrayList<Course> courseList = new ArrayList<Course>();

    // Constructor, Create DB
    public DatabaseHelper( Context context ) {
        super(context, DATABASE_NAME, null, 1) ;
    }

    // Create the MyCourses table
    public void onCreate( SQLiteDatabase db ) {
        db.execSQL("CREATE TABLE " + COURSE_TABLE + " (_id INTEGER PRIMARY KEY, "
                + KEY_COURSE_NUM + " TEXT, "
                + KEY_COURSE_NAME + " TEXT, "
                + KEY_COURSE_DESC + " TEXT, "
                + KEY_DATE + " TEXT, "
                + KEY_TIME + " TEXT, "
                + KEY_INSTRUCTOR + " TEXT)");
    }

    // Upgrade the MyCourses table
    public void onUpgrade( SQLiteDatabase db, int oldVersion, int newVersion ) {
        // Drop older table if it exists
        db.execSQL("DROP TABLE IF EXISTS " + COURSE_TABLE);

        // Create table again
        onCreate(db);
    }

    // Add a new course
    public void addCourse( Course course ) {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put(KEY_COURSE_NUM, course.getCourseNum());
        contentValues.put(KEY_COURSE_NAME, course.getCourseName());
        contentValues.put(KEY_COURSE_DESC, course.getCourseDesc());
        contentValues.put(KEY_DATE, course.getCourseDate());
        contentValues.put(KEY_TIME, course.getCourseTime());
        contentValues.put(KEY_INSTRUCTOR, course.getCourseInstructor());

        db.insert(COURSE_TABLE, null, contentValues);
        db.close();
    }

    // Get all courses, assign to array of course objects an return array
    public ArrayList<Course> getCourses() {
        courseList.clear();

        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery("SELECT * FROM " + COURSE_TABLE, null);

        // Loop through cursor, extract data and assign to item Course object
        if( cursor.getCount()!=0) {
            if( cursor.moveToFirst() ) {
                do {
                    Course item = new Course();
                    item.setCourseNum(cursor.getString(cursor.getColumnIndex(KEY_COURSE_NUM)));
                    item.setCourseName(cursor.getString(cursor.getColumnIndex(KEY_COURSE_NAME)));
                    item.setCourseDesc(cursor.getString(cursor.getColumnIndex(KEY_COURSE_DESC)));
                    item.setCourseDate(cursor.getString(cursor.getColumnIndex(KEY_DATE)));
                    item.setCourseTime(cursor.getString(cursor.getColumnIndex(KEY_TIME)));
                    item.setCourseInstructor(cursor.getString(cursor.getColumnIndex(KEY_INSTRUCTOR)));

                    // Add the object to the courseList array of Courses
                    courseList.add(item);
                } while( cursor.moveToNext());
            }
        }
        cursor.close();
        db.close();
        return courseList;
    }
}

Course.java

public class Course {
    private String courseNum;
    private String courseName;
    private String courseDesc;
    private String date;
    private String time;
    private String instructor;

    // Empty constructor
    public Course() {

    }

    // Constructor for new course
    public Course(Course course) {
        this.courseNum = course.courseNum;
        this.courseName = course.courseName;
        this.courseDesc = course.courseDesc;
        this.date = course.date;
        this.time = course.time;
        this.instructor = course.instructor;
    }

    // Get courseNum
    public String getCourseNum() {
        return courseNum;
    }

    // Set courseNum
    public void setCourseNum( String courseNum ) {
        this.courseNum = courseNum;
    }

    // Get courseName
    public String getCourseName() {
        return courseName;
    }

    // Set courseName
    public void setCourseName( String courseName ) {
        this.courseName = courseName;
    }

    // Get courseDesc
    public String getCourseDesc() {
        return courseDesc;
    }

    // Set courseDesc
    public void setCourseDesc( String courseDesc ) {
        this.courseDesc = courseDesc;
    }

    // Get date
    public String getCourseDate() {
        return date;
    }

    // Set date
    public void setCourseDate( String date ) {
        this.date = date;
    }

    // Get time
    public String getCourseTime() {
        return time;
    }

    // Set time
    public void setCourseTime( String time ) {
        this.time = time;
    }

    // Get instructor
    public String getCourseInstructor() {
        return instructor;
    }

    // Set instructor
    public void setCourseInstructor( String instructor ) {
        this.instructor = instructor;
    }
}

AddCourseActivity.java

import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;


public class AddCourseActivity extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_add_course);
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_add_course, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    // Called when Save button is pressed
    public void saveCourse(View v) {
        Course c = new Course();
        DatabaseHelper db = new DatabaseHelper(this);

        EditText num = (EditText) findViewById(R.id.courseNum);
        c.setCourseNum(num.getText().toString());
        EditText name = (EditText) findViewById(R.id.courseName);
        c.setCourseName(name.getText().toString());
        EditText desc = (EditText) findViewById(R.id.courseDesc);
        c.setCourseDesc(desc.getText().toString());
        EditText date = (EditText) findViewById(R.id.courseDate);
        c.setCourseDate(date.getText().toString());
        EditText time = (EditText) findViewById(R.id.courseTime);
        c.setCourseTime(time.getText().toString());
        EditText inst = (EditText) findViewById(R.id.courseInstructor);
        c.setCourseInstructor(inst.getText().toString());

        db.addCourse(c);

        // Return to Main Activity
        Intent intent = new Intent(v.getContext(), MainActivity.class);
        v.getContext().startActivity(intent);
    }

    // Called when Cancel button is pressed
    public void cancel(View v) {
        // Return to Main Activity
        Intent intent = new Intent(v.getContext(), MainActivity.class);
        v.getContext().startActivity(intent);
    }
}

activity_main.xml中

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">
    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:text="My Courses"
        android:textColor="#FFFFFF"
        android:textSize="30dp"
        android:background="#000000"/>

    <Button
        android:id="@+id/addCourse"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Add Course"
        android:onClick="onClick"/>

    <ListView
        android:id="@+id/course_list"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"></ListView>
</LinearLayout>

Activity_Add_Course.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">
    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:text="Add New Course"
        android:textColor="#FFFFFF"
        android:textSize="30dp"
        android:background="#000000"/>

    <EditText
        android:id="@+id/courseNum"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:hint="Course #"/>

    <EditText
        android:id="@+id/courseName"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:hint="Course Name"/>

    <EditText
        android:id="@+id/courseDesc"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:lines="6"
        android:hint="Course Description"/>

    <EditText
        android:id="@+id/courseDate"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:hint="Course Date"/>

    <EditText
        android:id="@+id/courseTime"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:hint="Course Time"/>

    <EditText
        android:id="@+id/courseInstructor"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:hint="Course Instructor"/>

    <Button
        android:id="@+id/saveCourse"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Save"
        android:onClick="saveCourse"/>

    <Button
        android:id="@+id/cancel"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Cancel"
        android:onClick="cancel"/>
</LinearLayout>

Android：在ListView中检索数据和显示

0 个答案: