我编写了一些代码，连接到设备内部存储器中的数据库，运行SQL语句以过滤摘录，然后迭代结果并创建一个列表，该列表可以在程序中稍后使用。但是，当使用日志语句检查时，该列表不会返回任何内容。我在迭代之前检查了SQL语句是否与日志语句一起工作，并且它返回了正确的行值。
package com.example.fit_world;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import android.content.res.AssetManager;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.util.Log;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.List;
import com.example.fit_world.Exercise;
public class GenerateWorkout extends AppCompatActivity {
private static final String DATABASE_NAME = "Exercises.db";
private SQLiteDatabase database;
private void copyDatabaseToInternalStorage() {
InputStream inputStream = null;
OutputStream outputStream = null;
try {
// Open the database file in the assets folder
AssetManager assetManager = getAssets();
inputStream = assetManager.open(DATABASE_NAME);
if (inputStream == null) {
throw new IOException("Failed to open file: " + DATABASE_NAME);
}
// Generate a unique file name for the database in the internal storage
File outputFile = new File(getFilesDir(), "Exercises_" + System.currentTimeMillis() + ".db");
// Check if the file already exists in the internal storage
if (outputFile.exists()) {
// Delete the file if it already exists
outputFile.delete();
}
outputStream = new FileOutputStream(outputFile);
// Copy the database file from the assets folder to the internal storage
byte[] buffer = new byte[1024];
int length;
while ((length = inputStream.read(buffer)) > 0) {
outputStream.write(buffer, 0, length);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
// Close the streams
try {
if (inputStream != null) {
inputStream.close();
}
if (outputStream != null) {
outputStream.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_generate_workout);
String equipmentType = "None";
String difficultyType = "Easy";
String weightGoalType = "Weight Loss";
List<Exercise> exercises = getExercisesFromDatabase(equipmentType, difficultyType, weightGoalType);
for (Exercise exercise : exercises) {
Log.d("LOL", exercise.toString());
}
}
private List<Exercise> getExercisesFromDatabase(String equipmentType, String difficultyType, String weightGoalType) {
List<Exercise> exercises = new ArrayList<>();
// Check if the database file exists in the internal storage
File databaseFile = new File(getFilesDir(), DATABASE_NAME);
if (!databaseFile.exists()) {
// If the database file does not exist, copy it from the assets folder
copyDatabaseToInternalStorage();
}
// Open the database file in the internal storage
SQLiteDatabase database = null;
Cursor cursor = null;
try {
// Open the database file in the internal storage
database = openOrCreateDatabase("Exercises.db", MODE_PRIVATE, null);
// Execute the query to retrieve the list of exercises
String query = "SELECT * FROM Exercises WHERE Equipment = ? AND Difficulty = ? AND Goal = ?";
String[] selectionArgs = new String[]{equipmentType, difficultyType, weightGoalType};
cursor = database.rawQuery(query, selectionArgs);
int rowCount = cursor.getCount();
System.out.print(rowCount);
Log.d("TAG", "Row count: " + rowCount);
Log.d("MMM", "Row count: " + database.rawQuery("SELECT * FROM exercises", null).getCount());
// Iterate through the result set and create a list of exercises
while (cursor.moveToNext()) {
int idColumnIndex = cursor.getColumnIndex("id");
int nameColumnIndex = cursor.getColumnIndex("name");
int descriptionColumnIndex = cursor.getColumnIndex("description");
int equipmentColumnIndex = cursor.getColumnIndex("equipment");
int difficultyColumnIndex = cursor.getColumnIndex("difficulty");
int weightGoalColumnIndex = cursor.getColumnIndex("weight_goal");
int requiredEquipmentColumnIndex = cursor.getColumnIndex("required_equipment");
int numberOfRepsColumnIndex = cursor.getColumnIndex("number_of_reps");
if (idColumnIndex != -1 && nameColumnIndex != -1 && descriptionColumnIndex != -1 && equipmentColumnIndex != -1 &&
difficultyColumnIndex != -1 && weightGoalColumnIndex != -1 && requiredEquipmentColumnIndex != -1 &&
numberOfRepsColumnIndex != -1) {
int id = cursor.getInt(idColumnIndex);
String name = cursor.getString(nameColumnIndex);
String description = cursor.getString(descriptionColumnIndex);
String equipment = cursor.getString(equipmentColumnIndex);
String difficulty = cursor.getString(difficultyColumnIndex);
String weightGoal = cursor.getString(weightGoalColumnIndex);
String requiredEquipment = cursor.getString(requiredEquipmentColumnIndex);
int numberOfReps = cursor.getInt(numberOfRepsColumnIndex);
Exercise exercise = new Exercise(id, name, description, equipment, difficulty, weightGoal, requiredEquipment, numberOfReps);
exercises.add(exercise);
Log.d("TAG", "Exercise name: " + name);
Log.d("TAG", "Exercise description: " + description);
Log.d("TAG", "Exercise equipment: " + equipment);
Log.d("TAG", "Number of exercises retrieved: " + exercises.size());
}
}
} catch (SQLException e) {
e.printStackTrace();
Log.e("TAG", "Error accessing database: " + e.getMessage());
} finally {
// Close the cursor and database
if (cursor != null) {
cursor.close();
}
if (database != null) {
database.close();
}
}
return exercises;
}
}我尝试使用日志语句来查看打印的摘录列表，但是没有任何内容打印到logcat，SQL语句的工作方式与我使用日志语句查看打印的值相同，并且工作正常
1条答案
按热度按时间3wabscal1#
我猜想，当有效数据存在时，确实会打印出一些东西，但不是预期的，因此可能会错过。
更具体地说，打印的内容取决于Exercise类的toString方法，该方法用于：-
它可能是
D/LOL: a.a.so75035530javasqliteemptylist.Exercise@58c3a3e（这是对您提供的代码的改编）除此之外，核心代码看起来很好。以下是adaptated代码，用于测试打开的数据库中的一些数据（单行）（只有一行）：-
公共类MainActivity扩展了AppCompatActivity {
}
getColumnIndex是大小写相关的））。：-
正如您所看到的，输出/结果与预期一致，但是最后一行是通过返回的List从循环中获得的，因此可能不是预期的结果。
但是，如果使用以下内容：-
那么输出将更容易识别：
正如您所说的，dumpCursor确实提取了预期的数据，那么最可能的问题是，至少有一个
??columnIndex索引值正在查找游标中没有的列，因此为-1，因此将不满足**if**语句（if (idColumnIndex != -1 && nameColumnIndex != ....）（检查dumpCursor输出是否告诉您实际的列名）int weightGoalColumnIndex = cursor.getColumnIndex("Goal");*（注意Goal专门用于产生-1（*。使用调试扩展光标，然后扩展mColumnNameMap显示：-getColumnIndex**方法区分大小写，因此要搜索的名称的大小写必须与游标中列的大小写匹配。