Question

我正在设置一个RecyclerView来查看数据库中数据的ArrayList（最初为空）。但是，它在Android虚拟设备中不断崩溃。我是Android Studio的新手，正在做一个个人项目。我使用了不同的书籍和视频来创作自己的作品。

我试图按字母顺序列出所有具有共同类别的数据。但如果数据不存在，则显示id / emptyView textView。

我认为我的错误可能是在适配器中，因为我在ViewHolder中选择了不正确的textView或在onCreateViewHolder中选择了不正确的通货膨胀布局，因为我对此感到有些困惑，他们应该指出这一点。或我的db.query游标中的错误。

Logcat：

FATAL EXCEPTION: main
Process: com.HSC.calendarfit, PID: 10164
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.HSC.calendarfit/com.HSC.calendarfit.ExerciseList}: android.database.sqlite.SQLiteException: unrecognized token: ""Arms ORDER BY exerciseName ASC" (code 1 SQLITE_ERROR): , while compiling: SELECT exerciseName FROM exerciseList WHERE muscleGroup = "Arms ORDER BY exerciseName ASC
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loop(Looper.java:193)
    at android.app.ActivityThread.main(ActivityThread.java:6669)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
 Caused by: android.database.sqlite.SQLiteException: unrecognized token: ""Arms ORDER BY exerciseName ASC" (code 1 SQLITE_ERROR): , while compiling: SELECT exerciseName FROM exerciseList WHERE muscleGroup = "Arms ORDER BY exerciseName ASC
    at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
    at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:903)
    at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:514)
    at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
    at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
    at android.database.sqlite.SQLiteQuery.<init>(SQLiteQuery.java:37)
    at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:46)
    at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1408)
    at android.database.sqlite.SQLiteDatabase.queryWithFactory(SQLiteDatabase.java:1255)
    at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1126)
    at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1294)
    at com.HSC.calendarfit.dbExerciseListHandler$override.getExercises(dbExerciseListHandler.java:65)
    at com.HSC.calendarfit.dbExerciseListHandler$override.access$dispatch(Unknown Source:64)
    at com.HSC.calendarfit.dbExerciseListHandler.getExercises(Unknown Source:15)
    at com.HSC.calendarfit.ExerciseList.onCreate(ExerciseList.java:43)
    at android.app.Activity.performCreate(Activity.java:7136)
    at android.app.Activity.performCreate(Activity.java:7127)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048) 
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808) 
    at android.os.Handler.dispatchMessage(Handler.java:106) 
    at android.os.Looper.loop(Looper.java:193) 
    at android.app.ActivityThread.main(ActivityThread.java:6669) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

在活动中调用适配器和方法：

       dbHandler = new dbExerciseListHandler(this, null, null, 1);
        muscleCategory = "Arms";
        List<dbExerciseList> list = dbHandler.getExercises(muscleCategory);
        recyclerView = (RecyclerView) findViewById(R.id.rvExerciseList);
        emptyView = (TextView) findViewById(R.id.emptyView);

        if (list.isEmpty()){
            recyclerView.setVisibility(View.GONE);
            emptyView.setVisibility(View.VISIBLE);
        }else{
            recyclerView.setVisibility(View.VISIBLE);
            emptyView.setVisibility(View.GONE);
        }

        recyclerView.setHasFixedSize(true);
        mAdapter = new ExerciseListAdapter(list);

        layoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);
        recyclerView.setAdapter(mAdapter);

数据库处理程序中用于获取数据并创建Arraylist的方法：

public List<dbExerciseList> getExercises(String muscleGroup){
        List<dbExerciseList> list = new ArrayList<>();
        SQLiteDatabase db = this.getWritableDatabase();
        String[] columnsToUse = {COLUMN_EXERCISENAME};
        Cursor cursor = db.query(TABLE_EXERCISE, columnsToUse, COLUMN_MUSCLEGROUP + " = \"" +
                        muscleGroup, null, null, null, COLUMN_EXERCISENAME + "ASC");
        while (cursor.moveToNext()){
            String exerciseName = cursor.getString(0);
            dbExerciseList name = new dbExerciseList(exerciseName);
            list.add(name);
        }
        return list;

    }

dbExerciseList有我的获取器和设置器。

RecyclerView适配器：

public class ExerciseListAdapter extends RecyclerView.Adapter<ExerciseListAdapter.ExerciseListViewHolder>{

    private List<dbExerciseList> mDataset;


    public class ExerciseListViewHolder extends RecyclerView.ViewHolder {
        public TextView tvExerciseName;
        public ExerciseListViewHolder(@NonNull View itemView) {
            super(itemView);
            tvExerciseName = itemView.findViewById(R.id.tvExerciseName);
        }
    }

    public ExerciseListAdapter(List<dbExerciseList> mDataset) {
        this.mDataset = mDataset;
    }

    @Override
    public ExerciseListViewHolder onCreateViewHolder( ViewGroup viewGroup, int i) {
        TextView v = (TextView) LayoutInflater.from(viewGroup.getContext()).
                inflate(R.layout.activity_exercise_list, viewGroup, false);
        return new ExerciseListViewHolder(v);
    }

    @Override
    public void onBindViewHolder(ExerciseListViewHolder exerciseListViewHolder, int position) {
        dbExerciseList item = mDataset.get(position);
        exerciseListViewHolder.tvExerciseName.setText(item.get_exerciseName());
    }

    @Override
    public int getItemCount() {
        return mDataset.size();
    }
}

谢谢。

Answer 1

在getExercises()内部，在此行：

Cursor cursor = db.query(TABLE_EXERCISE, columnsToUse, COLUMN_MUSCLEGROUP + " = \"" +
    muscleGroup, null, null, null, COLUMN_EXERCISENAME + "ASC");

这是什么：\" ？???
这将使该字符串：

SELECT exerciseName FROM exerciseList WHERE muscleGroup = "Arms ORDER BY exerciseName ASC

由于双引号在语法上是错误的。
更改为：

Cursor cursor = db.query(TABLE_EXERCISE, columnsToUse, COLUMN_MUSCLEGROUP 
    + " = '" + muscleGroup + "'", null, null, null, COLUMN_EXERCISENAME + "ASC");

（您要这样做吗？）
但是由于这种方式易于进行sql注入，因此更好地使用这种方式将参数传递给sql语句：

String strQuery = "SELECT " + COLUMN_EXERCISENAME + " FROM " + TABLE_EXERCISE + 
    " WHERE " + COLUMN_MUSCLEGROUP + " = ? ORDER BY " + COLUMN_EXERCISENAME + " ASC";
Cursor cursor = db.rawQuery(strQuery, new String[] {muscleGroup});

这样，您不必担心传递的参数类型。

在RecyclerView中显示SQLite DB arraylist一直崩溃

1 个答案: