创建一个用于在商店中查看宠物的应用程序，我在其中分别创建了一个数据库和一个名为shelter.db和pets的表。我创建了一个契约类来存储与数据库相关的所有常量，一个名为PetDbHelper的类扩展了SQLiteOpenHelper。我有两个活动CatalogActivity和EditorActivity。在CatalogActivity中，我正在尝试读取表格，在这里我尝试获取每列的列索引，但是名为“weight”的最后一列返回-1，这意味着您可能知道'没有列存在'并且在EditorActivity中，我我试图在桌子上插入宠物。我已经检查了所有内容，但不知道我的代码有什么问题。
这是PetContract类：
package com.example.android.pets.data;
import android.provider.BaseColumns;
public final class PetsContract {
public static final class PetEntry implements BaseColumns {
// CONSTANTS FOR TABLE AND COLUMN NAMES
public static final String TABLE_NAME = "pets";
public static final String _ID = BaseColumns._ID;
public static final String COLUMN_PET_NAME = "name";
public static final String COLUMN_PET_BREED = "breed";
public static final String COLUMN_PET_GENDER = "gender";
public static final String COLUMN_PET_WEIGHT = " weight";
// CONSTANTS FOR GENDER
public static final int GENDER_UNKNOWN = 0;
public static final int GENDER_MALE = 1;
public static final int GENDER_FEMALE = 2;
}
}
这是扩展SQLiteOpenHelper类的PetDbHelper：
package com.example.android.pets.data;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class PetDbHelper extends SQLiteOpenHelper {
private static final String DATABASE_NAME = "shelter.db";
private static final int DATABASE_VERSION = 1;
public PetDbHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
String CREATE_TABLE = "CREATE TABLE " + PetsContract.PetEntry.TABLE_NAME
+ " (" + PetsContract.PetEntry._ID + " INTEGER PRIMARY KEY AUTOINCREMENT, "
+ PetsContract.PetEntry.COLUMN_PET_NAME + " TEXT NOT NULL, "
+ PetsContract.PetEntry.COLUMN_PET_BREED + " TEXT, "
+ PetsContract.PetEntry.COLUMN_PET_GENDER + " INTEGER NOT NULL, "
+ PetsContract.PetEntry.COLUMN_PET_WEIGHT + " INTEGER NOT NULL DEFAULT 0);";
db.execSQL(CREATE_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
}
}
这是与数据库相关的CatalogActivity.java的代码：
/**
* Displays list of pets that were entered and stored in the app.
*/
public class CatalogActivity extends AppCompatActivity {
private PetDbHelper mDbHelper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_catalog);
mDbHelper = new PetDbHelper(this);
private void displayDatabaseInfo() {
// To access our database, we instantiate our subclass of
SQLiteOpenHelper
// and pass the context, which is the current activity.
// CREATE AND/OR OPEN A DATABASE TO READ FROM IT
SQLiteDatabase db = mDbHelper.getReadableDatabase();
// String[] projection = {PetEntry._ID, PetEntry.COLUMN_PET_NAME, PetEntry.COLUMN_PET_BREED, PetEntry.COLUMN_PET_GENDER, PetEntry.COLUMN_PET_WEIGHT};
Cursor cursor = db.query(PetEntry.TABLE_NAME, null, null, null, null, null, null);
//Cursor cursor = db.rawQuery("SELECT * FROM pets", null);
TextView displayView = (TextView) findViewById(R.id.text_view_pet);
try {
// Create a header in the Text View that looks like this:
//
// The pets table contains <number of rows in Cursor> pets.
// _id - name - breed - gender - weight
//
// In the while loop below, iterate through the rows of the cursor and display
// the information from each column in this order.
displayView.setText("The pets table contains " + cursor.getColumnCount() + " pets.\n\n");
displayView.append(PetEntry._ID + " - " +
PetEntry.COLUMN_PET_NAME + " - " +
PetEntry.COLUMN_PET_BREED + " - " +
PetEntry.COLUMN_PET_GENDER + " - " +
PetEntry.COLUMN_PET_WEIGHT );
// Figure out the index of each column
int idColumnIndex = cursor.getColumnIndex(PetEntry._ID);
int nameColumnIndex = cursor.getColumnIndex(PetEntry.COLUMN_PET_NAME);
int breedColumnIndex = cursor.getColumnIndex(PetEntry.COLUMN_PET_BREED);
int genderColumnIndex = cursor.getColumnIndex(PetEntry.COLUMN_PET_GENDER);
int weightColumnIndex = cursor.getColumnIndex(PetEntry.COLUMN_PET_WEIGHT);
Toast.makeText(this,
"weight_index ?" + weightColumnIndex + "\n"
+ "id_index" + idColumnIndex + "\n"
+ "name_index" + nameColumnIndex + "\n"
+ "breed_index" + breedColumnIndex + "\n"
+ "gender_index" + genderColumnIndex , Toast.LENGTH_LONG).show();
} finally {
// Always close the cursor when you're done reading from it. This releases all its
// resources and makes it invalid.
cursor.close();
}
}
@Override
protected void onStart() {
super.onStart();
displayDatabaseInfo();
}
我知道这是很多代码，这里是EditorActivity.java类的最后一段代码:(排除了与spinner对象相关的代码）
**
* Allows user to create a new pet or edit an existing one.
*/
public class EditorActivity extends AppCompatActivity {
/** EditText field to enter the pet's name */
private EditText mNameEditText;
/** EditText field to enter the pet's breed */
private EditText mBreedEditText;
/** EditText field to enter the pet's weight */
private EditText mWeightEditText;
/** EditText field to enter the pet's gender */
private Spinner mGenderSpinner;
/**
* Gender of the pet. The possible values are:
* 0 for unknown gender, 1 for male, 2 for female.
*/
private int mGender = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_editor);
// Find all relevant views that we will need to read user input from
mNameEditText = (EditText) findViewById(R.id.edit_pet_name);
mBreedEditText = (EditText) findViewById(R.id.edit_pet_breed);
mWeightEditText = (EditText) findViewById(R.id.edit_pet_weight);
mGenderSpinner = (Spinner) findViewById(R.id.spinner_gender);
}
private void addPet() {
String name = mNameEditText.getText().toString().trim();
String breed = mBreedEditText.getText().toString().trim();
int weight = Integer.parseInt(mWeightEditText.getText().toString().trim());
ContentValues values = new ContentValues();
values.put(COLUMN_PET_NAME, name);
values.put(COLUMN_PET_BREED, breed);
values.put(COLUMN_PET_GENDER, mGender);
values.put(COLUMN_PET_WEIGHT, weight);
PetDbHelper mDbHelper = new PetDbHelper(this);
SQLiteDatabase db = mDbHelper.getWritableDatabase();
long result = db.insert(TABLE_NAME, null, values);
if (result != -1) {
Toast.makeText(this, "Pet saved with id: " + result, Toast.LENGTH_SHORT).show();
} else {Toast.makeText(this, "Error with saving pet", Toast.LENGTH_SHORT).show();}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu options from the res/menu/menu_editor.xml file.
// This adds menu items to the app bar.
getMenuInflater().inflate(R.menu.menu_editor, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// User clicked on a menu option in the app bar overflow menu
switch (item.getItemId()) {
// Respond to a click on the "Save" menu option
case R.id.action_save:
// Save pet into the database
addPet();
// Exit the activity
finish();
return true;
// Respond to a click on the "Delete" menu option
case R.id.action_delete:
// Do nothing for now
return true;
// Respond to a click on the "Up" arrow button in the app bar
case android.R.id.home:
// Navigate back to parent activity (CatalogActivity)
NavUtils.navigateUpFromSameTask(this);
return true;
}
return super.onOptionsItemSelected(item);
}
}
在SQL中忽略前导空格但在地图键中很重要 - 列名称及其索引基本上存储在您可以使用getColumnIndex()访问的地图中。
public static final String COLUMN_PET_WEIGHT = " weight";
删除这里的前导空格。