我的问题是应用程序崩溃,不幸的是,该应用程序已停止。
mainActivity.java
public class MainActivity extends AppCompatActivity {
DatabaseHelper myDB;
Button btnAdd;
Button btnList;
TextView tvView;
EditText editText;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btnAdd = (Button) findViewById(R.id.btnAdd);
btnList = (Button) findViewById(R.id.btnList);
tvView = (TextView) findViewById(R.id.Textview);
editText = (EditText) findViewById(R.id.editText);
myDB=new DatabaseHelper(this);
btnAdd.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
String newEntry = editText.getText().toString();
if (newEntry.length() != 0) {
AddData(newEntry);
editText.setText("");
} else {
Toast.makeText(MainActivity.this, "You must put something in the text field", Toast.LENGTH_LONG).show();
}
}
});
btnList.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent intent = new Intent(MainActivity.this, ListDataActivity.class);
startActivity(intent);
}
});
}
public void AddData(String newEntry) {
boolean insertData = myDB.addData(newEntry);
// check inserted successfully
if (insertData == true) {
Toast.makeText(MainActivity.this, "Successfully Entered Data!", Toast.LENGTH_LONG).show();
} else {
Toast.makeText(MainActivity.this, "Something went wrong", Toast.LENGTH_LONG).show();
}
}
}
listAcitivity.java
公共类ListDataActivity扩展了AppCompatactivity {
DatabaseHelper myDB;
ListView listView;
ArrayAdapter<String>listAdapter;
@Override
protected void onCreate( Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.list_layout);
listView=(ListView)findViewById(R.id.listView);
myDB= new DatabaseHelper(this);
//populate an ArrayList<String> from the databases and then view it
ArrayList<String> theList=new ArrayList<>();
Cursor data=myDB.getListContent();
if(data.getCount()==0){
Toast.makeText(ListDataActivity.this,"The database was empty",Toast.LENGTH_LONG).show();
}else{
while(data.moveToNext()){
theList.add(data.getString(1));
listAdapter=new ArrayAdapter<>(this,android.R.layout.simple_list_item_1,theList);
listView.setAdapter(listAdapter);
}
}
}
databasehelper.java
公共类DatabaseHelper扩展了sqliteopenhelper {
public static final String DATABASE_NAME = "mylist.db";
public static final String TABLE_NAME = "mylist_data";
public static final String COL1 = "ID";
public static final String COL2 = "ITEM1";
public DatabaseHelper(Context context){
super (context, DATABASE_NAME, null , 1);
}
@Override
public void onCreate(SQLiteDatabase db) {
String createTable="CREATE TABLE"+ TABLE_NAME +"(ID INTEGER PRIMARY KEY AUTOINCREMENT,"+
"ITEM1 TEXT)";
db.execSQL(createTable);
db.close();
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP IF TABLE EXITS "+ TABLE_NAME);
onCreate(db);
db.close();
}
public boolean addData(String item1) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues contentValues = new ContentValues();
contentValues.put(COL2, item1);
long result = db.insert(TABLE_NAME, null, contentValues);
//if date as instered incorrectly it will return -1
if (result == -1) {
return false;
} else {
return true;
}
}
/**
* Return all the data from database
* @return
*/
public Cursor getListContent() {
SQLiteDatabase db = this.getWritableDatabase();
Cursor data =db.rawQuery("SELECT * FROM " + TABLE_NAME,null);
return data;
}
}
logcat show
12-27 07:29:26.268 24636-24636/sg.edu.rp.c346.todolist E/androidruntime:致命例外:主要 过程:sg.edu.rp.c346.todolist,pid:24636 java.lang.illegalstateException:尝试重新打开一个已经关闭的对象:sqlitedatabase:/data/data/sg.edu.rp.c346.todolist/databases/mylist.db at android.database.sqlite.sqliteclosable.acquirereference(sqliteclosable.java:55) at android.database.sqlite.sqlitedatabase.endtransaction(sqlitedatabase.java:520) at android.database.sqlite.sqliteopenhelper.getDatabaselocked(sqliteopenhelper.java:263) at android.database.sqlite.sqliteopenhelper.getWritabledatabase(sqliteopenhelper.java:164) 在sg.edu.rp.c346.todolist.databasehelper.addata(databasehelper.java:45) 在sg.edu.rp.c346.todolist.mainactivity.addata(mainActivity.java:58) 在sg.edu.rp.c346.todolist.mainactivity $ 1.ONCLICK(mainActivity.java:39) at android.view.view.performClick(view.java:4438) at android.view.view $ persionclick.run(view.java:18422) 在Android.os.handler.handlecallback(Handler.java:733) 在Android.os.handler.dispatchMessage(Handler.java:95) at android.os.looper.loop(looper.java:136) at android.app.activitythread.main(activityThread.java:5017) 在java.lang.reflect.method.invokenative(本机方法) 在java.lang.reflect.method.invoke(method.java:515) 在com.android.internal.os.os.zygoteinit $ methodandargscaller.run(zygoteinit.java:779) 在com.android.internal.os.os.zygoteinit.main(zygoteinit.java:595) 在dalvik.system.nativestart.main(本机方法)上12-27 07:29:28.078 24636-24636/?I/过程:发送信号。PID:24636 SIG:9
看起来您没有初始化myDB实例。
在尝试将条目添加到本地DB之前,请在onCreate
方法中调用myDB = new DatabaseHelper(this)
。
您必须在访问MyDB变量之前初始化MyDB变量。在您的MainActivity.java中,您不初始化助手类。
myDB= new DatabaseHelper(this);
只是这样做。也更改此条件
if (editText.length() != 0) { // Change this to newEntry.length() !=0
AddData(newEntry);
editText.setText("");
} else {
Toast.makeText(MainActivity.this, "You must put something in the text field", Toast.LENGTH_LONG).show();
}
希望这会起作用。
您不应在SQLiteOpenHelper
onCreate()
和onUpgrade()
中给您的close()
SQLiteDatabase
。只有close()
数据库处理您已获得的。