Android App从activities重写为fragments数据库报错

标签 android mysql android-fragments

我有一个应用程序，我可以在其中使用按钮和 Activity 进行导航。 现在我用滑动菜单和 fragment 重写了它。

到目前为止一切正常，但我的显示数据库条目的类(class)给了我一个 d`oh。

我似乎找不到错误。也许其他人会这样做:-)

Activity 代码:

import android.content.DialogInterface;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.ContextMenu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

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

public class anzeigen extends AppCompatActivity {

    private static final String TAG = anlegen.class.getSimpleName();
    private static final String FILENAME = TAG + ".kdf";
    private List valueList = new ArrayList<String>();
    final VorgangDataSource dataSource = new VorgangDataSource(this);


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

        Log.d(TAG,"Die Datenquelle wird geöffnet!");
        dataSource.open();

        final List<vorgangsdaten> vorgangsdatenList = dataSource.getAllVorgangsDaten();

        final ArrayAdapter<vorgangsdaten> VorgangArrayAdapter = new ArrayAdapter<>(
                this,
                R.layout.mylistlayout,
                vorgangsdatenList
        );


        final ListView lv = (ListView)findViewById(R.id.listView);
        lv.setAdapter(VorgangArrayAdapter);
        lv.setItemsCanFocus(false);
        lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, final int position, final long id) {
                String s_id = String.valueOf(id);
                Log.d(s_id,"id_in_onitem");

                String p_id = String.valueOf(position);
                Log.d(p_id,"position_on_item");

                final AlertDialog delete = new AlertDialog.Builder(anzeigen.this).create();
                delete.setTitle(getResources().getString(R.string.advice));
                delete.setMessage(getResources().getString(R.string.delete2dialog));
                delete.setIcon(R.drawable.warning);
                delete.setButton(DialogInterface.BUTTON_POSITIVE, getResources().getString(R.string.ok), new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        vorgangsdatenList.remove(position);
                        dataSource.deleteRow(id);
                        VorgangArrayAdapter.notifyDataSetChanged();
                        Toast.makeText(anzeigen.this,getResources().getString(R.string.eventdeleted),Toast.LENGTH_SHORT).show();
                    }
                });
                delete.setButton(DialogInterface.BUTTON_NEGATIVE, getResources().getString(R.string.cancel), new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        delete.closeOptionsMenu();
                    }
                });

                delete.show();

                /*vorgangsdatenList.remove(position);
                dataSource.deleteRow(id);
                VorgangArrayAdapter.notifyDataSetChanged();
                Toast.makeText(anzeigen.this,getResources().getString(R.string.eventdeleted),Toast.LENGTH_SHORT).show(); */
            }
        });
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        dataSource.close();
    }
}

fragment 代码:

import android.content.Context;
import android.content.DialogInterface;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.app.AlertDialog;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

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


public class frag_anzeigen extends Fragment {

    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";

    private String mParam1;
    private String mParam2;

    private OnFragmentInteractionListener mListener;


    private static final String TAG = frag_anlegen.class.getSimpleName();
    private static final String FILENAME = TAG + ".kdf";
    private List valueList = new ArrayList <String>();
    final VorgangDataSource dataSource = new VorgangDataSource(getActivity());


    public frag_anzeigen() {
        // Required empty public constructor
    }

    public static frag_anzeigen newInstance(String param1, String param2) {
        frag_anzeigen fragment = new frag_anzeigen();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        final View anzeigen = inflater.inflate(R.layout.frag_anzeigen,container,false);

        Log.d(TAG,"Die Datenquelle wird geöffnet!");
        dataSource.open();

        final List<vorgangsdaten> vorgangsdatenList = dataSource.getAllVorgangsDaten();

        final ArrayAdapter<vorgangsdaten> VorgangArrayAdapter = new ArrayAdapter< >(getActivity(),R.layout.mylistlayout,vorgangsdatenList);


        final ListView lv = (ListView)anzeigen.findViewById(R.id.listView);
        lv.setAdapter(VorgangArrayAdapter);
        lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, final int position, final long id) {
                String s_id = String.valueOf(id);
                Log.d(s_id,"id_in_onitem");

                String p_id = String.valueOf(position);
                Log.d(p_id,"position_on_item");

                final AlertDialog delete = new AlertDialog.Builder(getActivity()).create();
                delete.setTitle(getResources().getString(R.string.advice));
                delete.setMessage(getResources().getString(R.string.delete2dialog));
                delete.setIcon(R.drawable.warning);
                delete.setButton(DialogInterface.BUTTON_POSITIVE, getResources().getString(R.string.ok), new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        vorgangsdatenList.remove(position);
                        dataSource.deleteRow(id);
                        VorgangArrayAdapter.notifyDataSetChanged();
                        Toast.makeText(getActivity(), getResources().getString(R.string.eventdeleted), Toast.LENGTH_SHORT).show();
                    }
                });
                delete.setButton(DialogInterface.BUTTON_NEGATIVE, getResources().getString(R.string.cancel), new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        delete.closeOptionsMenu();
                    }
                });

                delete.show();
            }
        });
        return anzeigen;
    }

    public void onButtonPressed(Uri uri) {
        if (mListener != null) {
            mListener.onFragmentInteraction(uri);
        }
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof OnFragmentInteractionListener) {
            mListener = (OnFragmentInteractionListener) context;
        } else {
            throw new RuntimeException(context.toString()
                    + " must implement OnFragmentInteractionListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;

    }


    public interface OnFragmentInteractionListener {
        // TODO: Update argument type and name
        void onFragmentInteraction(Uri uri);
    }

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

错误消息

E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                Process: com.example..., PID: 14818
                                                                                java.lang.NullPointerException
                                                                                    at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:224)
                                                                                    at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164)
                                                                                    at com.example...VorgangDataSource.open(VorgangDataSource.java:146)
                                                                                    at com.example...frag_anzeigen.onCreateView(frag_anzeigen.java:86)
                                                                                    at android.support.v4.app.Fragment.performCreateView(Fragment.java:1974)
                                                                                    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
                                                                                    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252)
                                                                                    at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:742)
                                                                                    at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1617)
                                                                                    at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:517)
                                                                                    at android.os.Handler.handleCallback(Handler.java:733)
                                                                                    at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                    at android.os.Looper.loop(Looper.java:146)
                                                                                    at android.app.ActivityThread.main(ActivityThread.java:5679)
                                                                                    at java.lang.reflect.Method.invokeNative(Native Method)
                                                                                    at java.lang.reflect.Method.invoke(Method.java:515)
                                                                                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1291)
                                                                                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1107)
                                                                                    at dalvik.system.NativeStart.main(Native Method)

最佳答案

首先，这个问题之前已经回答过(Android Database Locked)，但无论如何......

在Activity , 你有

Log.d(TAG,"Die Datenquelle wird geöffnet!");
dataSource.open();

直到 onDestroy 才关闭它叫做。然后，在 Fragment ，您正在尝试再次打开数据库。有两种解决方案:

  1. 使用单例模式并在尝试打开它之前检查它是否已经打开。 Using Singleton design pattern for SQLiteDatabase

或

  1. 关闭dataSource一旦您不再需要它。

我会给你一个关于如何在你的项目中使用单例模式的快速指南。

在你的class延伸 SQLiteOpenHelper ，执行以下操作:

public class ClassName extends SQLiteOpenHelper {
    private static ClassName sInstance;

    public static synchronized ClassName getInstance() {
        if (sInstance == null) {
            sInstance = new DBOpenHelper(MyApplication.getAppContext());
        }
        return sInstance;
    }
}

并且在 VorgangDataSource类:

private SQLiteDatabase database;
private ClassName dbHelper;

public VorgangDataSource open(boolean readOnly) throws SQLException {
    dbHelper = ClassName.getInstance(); //Class name of the above class
    if (readOnly)
        database = dbHelper.getReadableDatabase();
    else
        database = dbHelper.getWritableDatabase();
    return this;
}

这是 MyApplication.java 的代码:

public class MyApplication extends Application {
    private static MyApplication INSTANCE;

    @Override
    public void onCreate() {
        super.onCreate();
        INSTANCE = this;
    }

    public static MyApplication getINSTANCE(){
        return INSTANCE;
    }

    public static Context getAppContext() {
        return INSTANCE.getApplicationContext();
    }
}

不要忘记添加 android:name=".MyApplication"属性给你的 <application>在AndroidManifest.xml .例如:

<application
        android:name=".MyApplication"
        ...>
        <activity ...

现在，您管理数据库应该容易多了。使用 isOpen()查看它是否已经打开的方法。希望这会有所帮助。

关于Android App从activities重写为fragments数据库报错，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/37663723/

上一篇：MySQL:查询在指定日期之前设置的不同字段的最新条目

下一篇：php - 使用 PHP 从 MySQL 正确显示多行文本

相关文章：

mysql - SQL动态删除MySQL列约束以防止列更新

mysql - 将多个查询与一个标准列组合

android - Viewpager 和 Tab 的滚动问题

android - 如何从 ListView 中获取所有选中的项目？

android - 如何在 android Canvas 上绘制实心三角形

java - 从应用程序启动 Google map

java - 为什么不添加外键约束groovy/grails

java - fragment : overwrite activities margin

java - 为什么我的 fragment 中的 Activity 上下文为空？

android - 使用 GridLayoutManager 将 Recycler View 转换为 Pdf

©2024 IT工具网  联系我们