将参数设置为rawQuery时的SQLiteException

Question

我在Google Play Console中收到了此崩溃报告，但我无法重现：

java.lang.RuntimeException: 
  at android.app.ActivityThread.performLaunchActivity (ActivityThread.java:2422)
  at android.app.ActivityThread.handleLaunchActivity (ActivityThread.java:2482)
  at android.app.ActivityThread.access$900 (ActivityThread.java:150)
  at android.app.ActivityThread$H.handleMessage (ActivityThread.java:1344)
  at android.os.Handler.dispatchMessage (Handler.java:102)
  at android.os.Looper.loop (Looper.java:148)
  at android.app.ActivityThread.main (ActivityThread.java:5423)
  at java.lang.reflect.Method.invoke (Method.java)
  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run (ZygoteInit.java:726)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:616)
Caused by: android.database.sqlite.SQLiteException: 
  at android.database.sqlite.SQLiteConnection.nativePrepareStatement (SQLiteConnection.java)
  at android.database.sqlite.SQLiteConnection.acquirePreparedStatement (SQLiteConnection.java:887)
  at android.database.sqlite.SQLiteConnection.prepare (SQLiteConnection.java:498)
  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:44)
  at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory (SQLiteDatabase.java:1316)
  at android.database.sqlite.SQLiteDatabase.rawQuery (SQLiteDatabase.java:1255)
  at .StatDB.getExercise (StatDB.java)
  at .ExerciseList.onCreate (ExerciseList.java)
  at android.app.Activity.performCreate (Activity.java:6294)
  at android.app.Instrumentation.callActivityOnCreate (Instrumentation.java:1108)
  at android.app.ActivityThread.performLaunchActivity (ActivityThread.java:2375)
  at android.app.ActivityThread.handleLaunchActivity (ActivityThread.java:2482)
  at android.app.ActivityThread.access$900 (ActivityThread.java:150)
  at android.app.ActivityThread$H.handleMessage (ActivityThread.java:1344)
  at android.os.Handler.dispatchMessage (Handler.java:102)
  at android.os.Looper.loop (Looper.java:148)
  at android.app.ActivityThread.main (ActivityThread.java:5423)
  at java.lang.reflect.Method.invoke (Method.java)
  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run (ZygoteInit.java:726)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:616)

这是我的getExercise方法：

public List<Bean> getExercise(String sub) {
        SQLiteDatabase db = initializer.getReadableDatabase();

        String sql = "SELECT * FROM " + sub;

        Cursor cursor = db.rawQuery(sql, null);

        List<Bean> exeList = new ArrayList<Bean>();
        while(cursor.moveToNext()) {
            String code = cursor.getString(1);
            String mark = cursor.getString(2);
            exeList.add(new Bean(code, mark));
        }

        cursor.close();
        db.close();
        return exeList;
    }

在我的ExerciseList.onCreate：

Intent i = getIntent();
        subCode = i.getExtras().getString("sub");
List<Bean> exeList = statDB.getExercise(subCode);

我之前曾提到“崩溃可能因为subCode是空的吗？但是在我进行测试后，我排除了这个原因。因为在List<Bean> exeList = statDB.getExercise(subCode);之前，实际上我用这个设置我的TextView：

if (subCode.equals("bd")) {
            passTv.setText("Some Text");
        } else {
            passTv.setText("Another Text");
        }

所以更完整的代码是：

Intent i = getIntent();
        subCode = i.getExtras().getString("sub");
if (subCode.equals("bd")) {
                passTv.setText("Some Text");
            } else {
                passTv.setText("Another Text");
            }
List<Bean> exeList = statDB.getExercise(subCode);

如果我的subcode为空，我的TextView将首先崩溃。所以问题是可疑的是我的getExercise方法，特别是String sql = "SELECT * FROM " + sub;。是因为参数sub没有通过？

Answer 1

根据您的问题：

崩溃是否因为subCode为空而发生？

如果你不知道如果sub是null会发生什么：

String sql = "SELECT * FROM " + sub;

好吧，检查很简单：

String sub = null;
String sql = "SELECT * FROM " + sub;
System.out.println(sql);

SELECT * FROM null

只需检查null值以防止发送错误的查询。

if(sub != null){
    throw new Exception("no table provided")
}
String sql = "SELECT * FROM " + sub;

这可能不是创建这样的查询的最佳方法。 首先，请参阅SQL注入。 那么，当你的表没有2个TEXT字段时会发生什么？您应该使用DAO模式为每个表创建一个类，而不是希望最好。