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社区首页 >问答首页 >用Java语言从SQLite值创建菜单

问用Java语言从SQLite值创建菜单
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Stack Overflow用户
提问于 2012-11-12 04:49:40
回答 3查看 280关注 0票数 0

我正在尝试使用来自SQLite数据库的数据创建一个ListMenu来定义每个MenuItem的名称。因此，在一个名为menu.java的类中，我定义了数组

代码语言：javascript
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String classes [] = {};

它应该包含每个菜单项的名称。

在一个DBAdapter类中，我创建了一个函数，这样用户就可以向表中插入信息(顺便说一下，这一切都很好用)。

代码语言：javascript
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public long insertContact(String name, String code, String location, String comments, int days, int start, int end, String type) 
    {
        ContentValues initialValues = new ContentValues();
        initialValues.put(KEY_NAME, name);
        initialValues.put(KEY_CODE, code);
        initialValues.put(KEY_LOCATION, location);
        initialValues.put(KEY_COMMENTS, comments);
        initialValues.put(KEY_DAYS, days);
        initialValues.put(KEY_START, start);
        initialValues.put(KEY_END, end);
        initialValues.put(KEY_TYPE, type);
        return db.insert(DATABASE_TABLE, null, initialValues);
    }

我需要用插入到KEY_NAME中的String来填充该String数组。有没有人知道这是否可能？

非常感谢你们的帮助。

如果我通过Sam/Mango实现该函数，程序会崩溃，是我错误地使用了它，还是由于数组大小未知而导致错误？

代码语言：javascript
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DBAdapter db = new DBAdapter(this);
String classes [] = db.getClasses();

编辑:我应该提一下，如果我手动定义数组：

代码语言：javascript
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String classes [] = {"test1", "test2", "test3", etc};

它工作得很好。错误是一个NullPointerException

这是logcat (很抱歉格式化有误)。我没有在getClasses()函数中初始化db = helper.getReadableDatabase()；，但不幸的是它没有解决这个问题。

代码语言：javascript
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11-11 22:53:39.117: D/dalvikvm(17856): Late-enabling CheckJNI
11-11 22:53:39.297: D/TextLayoutCache(17856): Using debug level: 0 - Debug Enabled: 0
11-11 22:53:39.337: D/libEGL(17856): loaded /system/lib/egl/libGLES_android.so
11-11 22:53:39.337: D/libEGL(17856): loaded /system/lib/egl/libEGL_adreno200.so
11-11 22:53:39.357: D/libEGL(17856): loaded /system/lib/egl/libGLESv1_CM_adreno200.so
11-11 22:53:39.357: D/libEGL(17856): loaded /system/lib/egl/libGLESv2_adreno200.so
11-11 22:53:39.387: I/Adreno200-EGLSUB(17856): <ConfigWindowMatch:2078>: Format RGBA_8888.
11-11 22:53:39.407: D/memalloc(17856): /dev/pmem: Mapped buffer base:0x5c66d000 size:36593664 offset:32825344 fd:65
11-11 22:53:39.417: E/(17856): Can't open file for reading
11-11 22:53:39.417: E/(17856): Can't open file for reading
11-11 22:53:39.417: D/OpenGLRenderer(17856): Enabling debug mode 0
11-11 22:53:39.477: D/memalloc(17856): /dev/pmem: Mapped buffer base:0x5ecd3000 size:40361984 offset:36593664 fd:68
11-11 22:53:40.507: D/memalloc(17856): /dev/pmem: Mapped buffer base:0x61451000 size:7254016 offset:3485696 fd:71
11-11 22:53:41.077: I/Adreno200-EGLSUB(17856): <ConfigWindowMatch:2078>: Format RGBA_8888.
11-11 22:53:41.077: D/memalloc(17856): /dev/pmem: Mapped buffer base:0x61c4c000 size:7725056 offset:7254016 fd:74
11-11 22:53:41.097: D/memalloc(17856): /dev/pmem: Mapped buffer base:0x623aa000 size:8196096 offset:7725056 fd:80
11-11 22:53:41.937: D/memalloc(17856): /dev/pmem: Mapped buffer base:0x62b7b000 size:8667136 offset:8196096 fd:83
11-11 22:53:41.977: D/memalloc(17856): /dev/pmem: Unmapping buffer base:0x61c4c000 size:7725056 offset:7254016
11-11 22:53:41.977: D/memalloc(17856): /dev/pmem: Unmapping buffer base:0x623aa000 size:8196096 offset:7725056
11-11 22:53:41.977: D/memalloc(17856): /dev/pmem: Unmapping buffer base:0x62b7b000 size:8667136 offset:8196096
11-11 22:53:42.167: I/Adreno200-EGLSUB(17856): <ConfigWindowMatch:2078>: Format RGBA_8888.
11-11 22:53:42.177: D/memalloc(17856): /dev/pmem: Mapped buffer base:0x61c5d000 size:17084416 offset:13316096 fd:74
11-11 22:53:42.317: D/memalloc(17856): /dev/pmem: Mapped buffer base:0x63853000 size:20852736 offset:17084416 fd:80
11-11 22:53:42.357: D/OpenGLRenderer(17856): Flushing caches (mode 0)
11-11 22:53:42.357: D/memalloc(17856): /dev/pmem: Unmapping buffer base:0x5c66d000 size:36593664 offset:32825344
11-11 22:53:42.357: D/memalloc(17856): /dev/pmem: Unmapping buffer base:0x5ecd3000 size:40361984 offset:36593664
11-11 22:53:42.367: D/memalloc(17856): /dev/pmem: Unmapping buffer base:0x61451000 size:7254016 offset:3485696
11-11 22:53:42.757: D/memalloc(17856): /dev/pmem: Mapped buffer base:0x5c56d000 size:24621056 offset:20852736 fd:65
11-11 22:53:44.247: D/AndroidRuntime(17856): Shutting down VM
11-11 22:53:44.247: W/dalvikvm(17856): threadid=1: thread exiting with uncaught exception (group=0x40ac3210)
11-11 22:53:44.257: E/AndroidRuntime(17856): FATAL EXCEPTION: main
11-11 22:53:44.257: E/AndroidRuntime(17856): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{x.x.timetable/x.x.timetable.menu}: java.lang.NullPointerException
11-11 22:53:44.257: E/AndroidRuntime(17856):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1891)
11-11 22:53:44.257: E/AndroidRuntime(17856):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1992)
11-11 22:53:44.257: E/AndroidRuntime(17856):    at android.app.ActivityThread.access$600(ActivityThread.java:127)
11-11 22:53:44.257: E/AndroidRuntime(17856):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1158)
11-11 22:53:44.257: E/AndroidRuntime(17856):    at android.os.Handler.dispatchMessage(Handler.java:99)
11-11 22:53:44.257: E/AndroidRuntime(17856):    at android.os.Looper.loop(Looper.java:137)
11-11 22:53:44.257: E/AndroidRuntime(17856):    at android.app.ActivityThread.main(ActivityThread.java:4441)
11-11 22:53:44.257: E/AndroidRuntime(17856):    at java.lang.reflect.Method.invokeNative(Native Method)
11-11 22:53:44.257: E/AndroidRuntime(17856):    at java.lang.reflect.Method.invoke(Method.java:511)
11-11 22:53:44.257: E/AndroidRuntime(17856):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:823)
11-11 22:53:44.257: E/AndroidRuntime(17856):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:590)
11-11 22:53:44.257: E/AndroidRuntime(17856):    at dalvik.system.NativeStart.main(Native Method)
11-11 22:53:44.257: E/AndroidRuntime(17856): Caused by: java.lang.NullPointerException
11-11 22:53:44.257: E/AndroidRuntime(17856):    at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:221)
11-11 22:53:44.257: E/AndroidRuntime(17856):    at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:157)
11-11 22:53:44.257: E/AndroidRuntime(17856):    at x.x.timetable.DBAdapter.getClasses(DBAdapter.java:151)
11-11 22:53:44.257: E/AndroidRuntime(17856):    at x.x.timetable.menu.<init>(menu.java:15)
11-11 22:53:44.257: E/AndroidRuntime(17856):    at java.lang.Class.newInstanceImpl(Native Method)
11-11 22:53:44.257: E/AndroidRuntime(17856):    at java.lang.Class.newInstance(Class.java:1319)
11-11 22:53:44.257: E/AndroidRuntime(17856):    at android.app.Instrumentation.newActivity(Instrumentation.java:1023)
11-11 22:53:44.257: E/AndroidRuntime(17856):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1882)
11-11 22:53:44.257: E/AndroidRuntime(17856):    ... 11 more
11-11 22:53:46.527: I/Process(17856): Sending signal. PID: 17856 SIG: 9



package x.x.timetable;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class DBAdapter {
    static final String KEY_ROWID = "_id";
    static final String KEY_NAME = "name";
    static final String KEY_CODE = "code";
    static final String KEY_LOCATION = "location";
    static final String KEY_COMMENTS = "comments";
    static final String KEY_DAYS = "days";
    static final String KEY_START = "start";
    static final String KEY_END = "end";
    static final String KEY_TYPE = "type";


    static final String TAG = "DBAdapter";

    static final String DATABASE_NAME = "MyDB";
    static final String DATABASE_TABLE = "timetable";
    static final int DATABASE_VERSION = 2;

    static final String DATABASE_CREATE =
        "create table timetable (_id integer primary key autoincrement, "
        + "name text not null, code text not null, location text not null, comments text not null, days INTEGER not null, start INTEGER not null, end INTEGER not null, type text not null);";

    final Context context;

    DatabaseHelper DBHelper;
    SQLiteDatabase db;

    public DBAdapter(Context ctx)
    {
        this.context = ctx;
        DBHelper = new DatabaseHelper(context);
    }

    private static class DatabaseHelper extends SQLiteOpenHelper
    {
        DatabaseHelper(Context context)
        {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }

        @Override
        public void onCreate(SQLiteDatabase db)
        {
            try {
                db.execSQL(DATABASE_CREATE);
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
        {
            Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
                    + newVersion + ", which will destroy all old data");
            db.execSQL("DROP TABLE IF EXISTS timetable");
            db.execSQL("DROP TABLE IF EXISTS contacts");
            onCreate(db);
        }
    }

    //---opens the database---
    public DBAdapter open() throws SQLException 
    {
        db = DBHelper.getWritableDatabase();
        return this;
    }

    //---closes the database---
    public void close() 
    {
        DBHelper.close();
    }

    public int count(){
        db = DBHelper.getWritableDatabase();
        String count = "SELECT count(*) FROM table";
        Cursor mcursor = db.rawQuery(count, null);
        int icount = mcursor.getInt(0);
        return icount;
    }

    //---insert a contact into the database---
    public long insertContact(String name, String code, String location, String comments, int days, int start, int end, String type) 
    {
        ContentValues initialValues = new ContentValues();
        initialValues.put(KEY_NAME, name);
        initialValues.put(KEY_CODE, code);
        initialValues.put(KEY_LOCATION, location);
        initialValues.put(KEY_COMMENTS, comments);
        initialValues.put(KEY_DAYS, days);
        initialValues.put(KEY_START, start);
        initialValues.put(KEY_END, end);
        initialValues.put(KEY_TYPE, type);
        return db.insert(DATABASE_TABLE, null, initialValues);
    }

    //---deletes a particular contact---
    public boolean deleteContact(long rowId) 
    {
        return db.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0;
    }

    //---retrieves all the Timetable---
    public Cursor getAllTimetable()
    {
        return db.query(DATABASE_TABLE, new String[] {KEY_ROWID, KEY_NAME,
                KEY_CODE, KEY_LOCATION, KEY_COMMENTS, KEY_DAYS, KEY_START, KEY_END, KEY_TYPE}, null, null, null, null, null);
    }

    //---retrieves a particular contact---
    public Cursor getContact(long rowId) throws SQLException 
    {
        Cursor mCursor =
                db.query(true, DATABASE_TABLE, new String[] {KEY_ROWID,
                KEY_NAME, KEY_CODE, KEY_LOCATION, KEY_COMMENTS, KEY_DAYS, KEY_START, KEY_END, KEY_TYPE}, KEY_ROWID + "=" + rowId, null,
                null, null, null, null);
        if (mCursor != null) {
            mCursor.moveToFirst();
        }
        return mCursor;
    }

    //---updates a contact---
    public boolean updateContact(long rowId, String name, String code, String location, String comments, int days, int start, int end, String type) 
    {
        ContentValues args = new ContentValues();
        args.put(KEY_NAME, name);
        args.put(KEY_CODE, code);
        args.put(KEY_LOCATION, location);
        args.put(KEY_COMMENTS, comments);
        args.put(KEY_DAYS, days);
        args.put(KEY_START, start);
        args.put(KEY_END, end);
        args.put(KEY_TYPE, type);
        return db.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0;
    }

    public String[] getClasses() {

        db = DBHelper.getWritableDatabase();
        String[] columns = {KEY_NAME};
        Cursor c = db.query(DATABASE_TABLE, columns, null, null, null, null, null);
        String[] classes = new String [c.getCount()];
        int i = 0;
        while (c.moveToNext()) {
            classes[i] = c.getString(0);
            i++;
        }
        c.close();
        return classes; 
    }
}
java
android
sqlite
EN

回答 3

Stack Overflow用户

回答已采纳

发布于 2012-11-12 05:06:15

这绝对是有可能的。您可以在数据库类中创建一个以字符串数组形式返回值的方法。

代码语言：javascript
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public String[] getClasses() {
    String[] columns = {KEY_NAME};
    Cursor c = db.query(DATABASE_TABLE, columns, null, null, null, null, null);
    String[] classes = new String [c.getCount()];
    int i = 0;
    while (c.moveToNext()) {
        classes[i] = c.getString(0);
        i++;
    }
    c.close();
    return classes; 
}
票数 1
EN

Stack Overflow用户

发布于 2012-11-12 05:04:20

你要找的是

代码语言：javascript
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ArrayList<String> list= new ArrayList<String>();
list.add(name);

当您不知道数据结构中需要添加的元素的长度或数量时，您不应该在许多情况下(不是所有情况)使用数组。请改用ArrayList。要从列表中获取名称，请执行以下操作

代码语言：javascript
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list.get(ELEMENT_AT);

如果必须需要数组，请首先填充列表，然后使用List.toArray();返回数组。

票数 1
EN

Stack Overflow用户

发布于 2012-11-12 06:44:26

根据我们在评论中的讨论，我假设您想在onCreate()中做类似这样的事情

代码语言：javascript
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public class menu extends ListActivity{
    DBAdapter db;
    String[] classes; // = {"test", "test11", "test1", "test2", "test3",};

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        db = new DBAdapter(this);
        db.open();
        classes = db.getClasses();
        setListAdapter(new ArrayAdapter<String>(menu.this, android.R.layout.simple_list_item_1, classes));
    }

这显然使用了我帮助芒果编写的方法。

票数 1
EN
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：

https://stackoverflow.com/questions/13335316

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