我的应用程序（在此阶段）通过Java动态生成最多8个按钮但是，我没有存储用户生成的按钮数量的数据库。目前，如果用户生成大约5个按钮，则在用户退出应用程序时它们将全部丢失。我浏览了一堆SQLite教程，但我的问题与示例有点不同。
我的问题是我想获取用户生成的按钮数量并将它们存储在SQLite表中。以下是我的代码。
这是我的Mainactivity.java：
public class MainActivity extends AppCompatActivity {
int counter = 0;
FloatingActionButton addingSemester;
Button semesterButton;
LinearLayout semesterLayout;
GridLayout semesterGridLayout;
LinearLayout.LayoutParams portraitLayoutParams = new LinearLayout.LayoutParams(
AppBarLayout.LayoutParams.MATCH_PARENT,
AppBarLayout.LayoutParams.WRAP_CONTENT);
SemesterDBHelper mDbHelper;
SQLiteDatabase db;
ContentValues values;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mDbHelper = new SemesterDBHelper(this);
db = mDbHelper.getWritableDatabase();
values = new ContentValues();
addingSemester = (FloatingActionButton) findViewById(R.id.addActionButton);
semesterLayout = (LinearLayout) findViewById(R.id.main_layout);
semesterGridLayout = (GridLayout) findViewById(R.id.semester_grid_layout);
semesterButton = new Button(MainActivity.this);
if (savedInstanceState != null) {
counter = savedInstanceState.getInt("counter");
for (int i = 0; i < counter; i++) {
addSemesterButton(i);
}
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater menuInflater = getMenuInflater();
menuInflater.inflate(R.menu.main, menu);
return super.onCreateOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.delete) {
new AlertDialog.Builder(MainActivity.this)
.setTitle("Delete entry")
.setMessage("Are you sure you want to delete everything?")
.setCancelable(true)
.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
if (MainActivity.this.getResources().getBoolean(R.bool.is_landscape)) {
if (semesterGridLayout.getChildCount() > 0) {
semesterGridLayout.removeAllViews();
} else {
Toast.makeText(MainActivity.this, "There is nothing to delete", Toast.LENGTH_SHORT).show();
}
} else if (!MainActivity.this.getResources().getBoolean(R.bool.is_landscape)) {
if (semesterLayout.getChildCount() > 0) {
semesterLayout.removeAllViews();
} else {
Toast.makeText(MainActivity.this, "There is nothing to delete", Toast.LENGTH_SHORT).show();
}
}
counter = 0;
}
})
.setNegativeButton("No", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
})
.show();
return true;
}
return super.onOptionsItemSelected(item);
}
public void addSemesterButton(int id) {
Display display = getWindowManager().getDefaultDisplay();
Point size = new Point();
display.getSize(size);
double width = (size.x) / 3;
semesterButton = new Button(MainActivity.this);
semesterButton.setId(id + 1);
semesterButton.setText("Semester " + (id + 1));
semesterButton.setBackgroundColor(getColor(R.color.colorPrimary));
semesterButton.setTextColor(Color.WHITE);
portraitLayoutParams.setMargins(24, 24, 24, 24);
if (MainActivity.this.getResources().getBoolean(R.bool.is_landscape)) {
GridLayout.LayoutParams params = new GridLayout.LayoutParams();
params.setMargins(24, 24, 24, 24);
params.width = (int) width;
params.height = GridLayout.LayoutParams.WRAP_CONTENT;
semesterButton.setLayoutParams(params);
semesterGridLayout.addView(semesterButton);
} else if (!MainActivity.this.getResources().getBoolean(R.bool.is_landscape)) {
semesterLayout.addView(semesterButton);
semesterButton.setLayoutParams(portraitLayoutParams);
}
setOnLongClickListenerForSemesterButton();
setOnClickListenerForSemesterButton(counter);
}
public void onFloatActionButtonClick(View view) {
if (counter < 8) {
addSemesterButton(counter);
counter++;
values.put(SemesterContract.SemesterEntry.COLUMN_SEMESTER_NAME, "semester " + counter);
db.insert(SemesterContract.SemesterEntry.TABLE_NAME, null, values);
setOnLongClickListenerForSemesterButton();
} else if (counter == 8) {
Toast.makeText(MainActivity.this, "You cannot add more than 8 semesters", Toast.LENGTH_SHORT).show();
} else if (counter == 0) {
}
}
@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
savedInstanceState.putInt("counter", counter);
super.onSaveInstanceState(savedInstanceState);
}
private void setOnClickListenerForSemesterButton(int id){
semesterButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, SemesterBuilderActivity.class);
intent.putExtra("someKey", 1);
startActivity(intent);
}
});
}
private void setOnLongClickListenerForSemesterButton() {
semesterButton.setOnLongClickListener(new View.OnLongClickListener() {
@Override
public boolean onLongClick(View v) {
final Button b = (Button) v;
b.setTag(b.getText().toString());
b.setBackgroundColor(Color.RED);
b.setText("Delete");
AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
builder.setTitle("Delete entry");
builder.setMessage("Are you sure you want to delete this entry?");
builder.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
if (MainActivity.this.getResources().getBoolean(R.bool.is_landscape)) {
semesterGridLayout.removeView(b);
for (int i = 0; i < semesterGridLayout.getChildCount(); i++) {
((Button) semesterGridLayout.getChildAt(i)).setText("Semester " + (i + 1));
}
} else if (!MainActivity.this.getResources().getBoolean(R.bool.is_landscape)) {
semesterLayout.removeView(b);
for (int i = 0; i < semesterLayout.getChildCount(); i++) {
((Button) semesterLayout.getChildAt(i)).setText("Semester " + (i + 1));
}
}
counter--;
}
});
builder.setNegativeButton("No", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
b.cancelLongPress();
b.setBackgroundColor(ContextCompat.getColor(MainActivity.this, R.color.colorPrimary));
b.setText(b.getTag().toString());
dialog.cancel();
}
});
builder.show();
return true;
}
});
}
}
这是我的DBHelper类：
public class SemesterDBHelper extends SQLiteOpenHelper{
public SemesterDBHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
public static final String DATABASE_NAME = "semesters.db";
public static final int DATABASE_VERSION = 1;
private static final String SQL_DELETE_ENTRIES =
"DROP TABLE IF EXISTS " + SemesterContract.SemesterEntry.TABLE_NAME;
@Override
public void onCreate(SQLiteDatabase db) {
String SQL_CREATE_SEMESTER_TABLE = "CREATE TABLE " + SemesterContract.SemesterEntry.TABLE_NAME + " ("
+ SemesterContract.SemesterEntry._ID + " INTEGER PRIMARY KEY AUTOINCREMENT, "
+ SemesterContract.SemesterEntry.COLUMN_SEMESTER_NAME + " TEXT NOT NULL";
db.execSQL(SQL_CREATE_SEMESTER_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
}
这是我的合同：
public final class SemesterContract {
private SemesterContract(){}
public static final class SemesterEntry implements BaseColumns{
public static final String TABLE_NAME = "semesters";
public static final String _ID = BaseColumns._ID;
public static final String COLUMN_SEMESTER_NAME = "semester";
}
}
这是我得到的堆栈跟踪：
FATAL EXCEPTION: main
Process: myapp.onur.journeygpacalculator, PID: 28196
java.lang.RuntimeException: Unable to start activity ComponentInfo{myapp.onur.journeygpacalculator/myapp.onur.journeygpacalculator.MainActivity}: android.database.sqlite.SQLiteException: near "NULL": syntax error (code 1): , while compiling: CREATE TABLE semesters (_id INTEGER PRIMARY KEY AUTOINCREMENT, semester TEXT NOT NULL
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2787)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1504)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6247)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:872)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:762)
Caused by: android.database.sqlite.SQLiteException: near "NULL": syntax error (code 1): , while compiling: CREATE TABLE semesters (_id INTEGER PRIMARY KEY AUTOINCREMENT, semester TEXT NOT NULL
at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:895)
at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:506)
at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:726)
at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
at android.database.sqlite.SQLiteStatement.<init>(SQLiteStatement.java:31)
at android.database.sqlite.SQLiteDatabase.executeSql(SQLiteDatabase.java:1785)
at android.database.sqlite.SQLiteDatabase.execSQL(SQLiteDatabase.java:1716)
at myapp.onur.journeygpacalculator.data.SemesterDBHelper.onCreate(SemesterDBHelper.java:28)
at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:251)
at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:163)
at myapp.onur.journeygpacalculator.MainActivity.onCreate(MainActivity.java:52)
修改
这是我试图读取数据。我认为我没有正确实现它，但我试图创建光标。
这些是全球性的：
String[] projection = {
SemesterContract.SemesterEntry._ID,
SemesterContract.SemesterEntry.COLUMN_SEMESTER_NAME
};
String selection = SemesterContract.SemesterEntry.COLUMN_SEMESTER_NAME + " = ?";
String[] selectionArgs = { "My Semester" };
String sortOrder = SemesterContract.SemesterEntry.COLUMN_SEMESTER_NAME + " DESC";
这是我的onCreate：
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mDbHelper = new SemesterDBHelper(this);
db = mDbHelper.getWritableDatabase();
values = new ContentValues();
addingSemester = (FloatingActionButton) findViewById(R.id.addActionButton);
semesterLayout = (LinearLayout) findViewById(R.id.main_layout);
semesterGridLayout = (GridLayout) findViewById(R.id.semester_grid_layout);
semesterButton = new Button(MainActivity.this);
if (savedInstanceState != null) {
counter = savedInstanceState.getInt("counter");
for (int i = 0; i < counter; i++) {
addSemesterButton(i);
}
}
Cursor cursor = db.query(
SemesterContract.SemesterEntry.TABLE_NAME,// The table to query
projection, // The columns to return
selection, // The columns for the WHERE clause
selectionArgs, // The values for the WHERE clause
null, // don't group the rows
null, // don't filter by row groups
sortOrder // The sort order
);
}
答案 0 :(得分：0)
String SQL_CREATE_SEMESTER_TABLE = "CREATE TABLE " + SemesterContract.SemesterEntry.TABLE_NAME + " ("
+ SemesterContract.SemesterEntry._ID + " INTEGER PRIMARY KEY AUTOINCREMENT, "
+ SemesterContract.SemesterEntry.COLUMN_SEMESTER_NAME + " TEXT NOT NULL";
替换
String SQL_CREATE_SEMESTER_TABLE = "CREATE TABLE " + SemesterContract.SemesterEntry.TABLE_NAME + " ("
+ SemesterContract.SemesterEntry._ID + " INTEGER PRIMARY KEY AUTOINCREMENT, "
+ SemesterContract.SemesterEntry.COLUMN_SEMESTER_NAME + " TEXT NOT NULL)";
对于数据保存和获取，您必须为此编写相同的函数，请查看本教程，了解如何在sqlite中保存和获取数据https://developer.android.com/training/basics/data-storage/databases.html