android fragment sqlite查询崩溃

Question

这个问题在这里已经有了答案:





Unfortunately MyApp has stopped. How can I solve this?

(22 个回答)


6年前关闭。




我已经成功使用了一段时间的 sqlite 查询。但是，当我将这些代码迁移到另一个 APP 的 fragment 中时。查询后代码将立即崩溃。进入这些代码时，变量似乎没问题。我的猜测是“上下文”之类的东西没有给出正确的值，但是，我找不到它。以下是代码，请帮助我找到问题。

问题已解决:忘记将​​文件从 Assets 复制到数据库目录。

fragment .java

import android.content.Context;
import android.database.Cursor;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ListView;

public class Fragment1 extends Fragment {

    private int position;
    private ListView lv;
    private static dbOperator dbOp;
    private Cursor cursor;
    private Context context;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        context=getActivity();

        View rootView = inflater.inflate(R.layout.fragment_list, container, false);
        lv=(ListView) rootView.findViewById(R.id.list);
        dbOp = new dbOperator(context);
        dbOp.open();

        fillListChatrooms();   

        return rootView;

    }


    @Override
    public void onDestroyView(){
        dbOp.close();
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

    }

    private void fillListChatrooms() {

        int visibility;

        cursor = dbOp.readChatrooms(); 
        ListAdapterChatrooms adapter = new ListAdapterChatrooms(context, cursor, dbOp);

        lv.setAdapter(adapter);
    }
}

dbOperator.java

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.os.Environment;

import java.io.IOException;
import java.util.Locale;

public class dbOperator {


    private static final String dbName_friends = "friends.db";

    private static final int dbVersion= 1;

    public static final String tableCategories = "categories";
    public static final String columnIDC = "id_c";

    public static final String tableInterests = "interests";
    public static final String columnIDI = "id_i";


    public static final String columnIDU = "id_u";
    public static final String columnName = "name";
    public static final String columnLastChatTimestamp = "last_chat_timestamp";
    public static final String columnMatchedPercentage = "matched_percentage";
    public static final String columnIcon = "icon";
    public static final String columnChatLog = "chat_log";


    public static final String columnIDD = "id_d";
    public static final String columnTimestamp = "timestamp";
    public static final String columnContentFile = "content_file";

    public static final String tableChatrooms = "chatrooms";
    public static final String columnIDCR = "id_cr";
    public static final String columnChatType = "type";
    public static final String columnUnreadMessages = "unread_messages";


    private String language;

    private final Context context;
    private dbOpenHelper dbHelper_friends;
    private SQLiteDatabase  db_friends;

    private final String sdPath;

    private String dbPath_friends ;

    private static boolean flagDbModified_friends=false;


    dbOperator(Context ctx){
        context=ctx;


        dbPath_friends = ctx.getDatabasePath(dbName_friends).getPath();

        sdPath= Environment.getExternalStorageDirectory().getPath();
        Locale current= ctx.getResources().getConfiguration().locale;
        language=current.getCountry();

        switch (language)
        {
            case "de":
                break;
            case "zh-rTW":
                language="tw";
               break;
            default:
                language="en";
                break;
        }

    }

    public String getLanguage()
    {
        return language;
    }

    public void open() throws SQLException {

        boolean flagDBexist;

        flagDBexist=fileOp.checkFileExist(dbPath_friends);
        if (!flagDBexist )  copyDBfromServer(dbName_friends);
        dbHelper_friends= new dbOpenHelper(context, dbName_friends );
        db_friends=dbHelper_friends.getWritableDatabase();


    }

    public void close() {

        dbHelper_friends.close();
    }

    private void copyDBfromServer(String dbName)
    {

    }

    private void backupDB(String source, String target) throws IOException{

        fileOp.copyFile(source, target);

    }

    public Cursor readChatrooms(){

     Cursor c;
        // Below is where the crash start
c=db_friends.query(tableChatrooms,null,null,null,null,null,columnChatType); 

        return c;

    }




    public class dbOpenHelper extends SQLiteOpenHelper {

        public dbOpenHelper(Context context, String dbName) {
            super(context, dbName, null, dbVersion);
            //  super(context, name, factory, version);
            // TODO Auto-generated constructor stub
        }

        @Override
        public void onCreate(SQLiteDatabase sqldb) {
            // TODO Auto-generated method stub



        }


        @Override
        public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) {
            // TODO Auto-generated method stub

        }
    }
}

Answer 1

调用 fragment 的 onActivityCreated() 方法

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

    context=getActivity()
    dbOp = new dbOperator(context);
    dbOp.open();
    fillListChatrooms(); 
    }