[英]Extracting data from SQLite database (Android)
我無法在主要活動中將數據寫入數據庫,但是在其他活動中讀取和顯示數據時遇到問題。 我正在將SQLHelperDatabase類與“ addData”方法(根據調試器工作正常)和showData方法(這就是問題所在)一起使用。 在主要活動中輸入數據后,我希望能夠按發送消息按鈕,並在新活動中顯示數據。 我已經在這個問題上停留了一個星期,我一直在搜索WWW,每個教程都說我的代碼應該可以工作。 請有人可以幫助我深入了解這一令人沮喪的磨難。
package com.doors.waynderful.myapp;
import android.content.Intent;
import android.database.Cursor;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;
public class DisplayMessageActivity extends ActionBarActivity {
DatabaseHelper db;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
db = new DatabaseHelper(this);
Cursor cursor = db.showData();
cursor.moveToFirst();
String nam = cursor.getString(cursor.getColumnIndex(DatabaseHelper.THE_TABLE_COLUMN_NAME));
if (!cursor.isClosed()){
cursor.close();
}
TextView textView = new TextView(this);
textView.setTextSize(40);
textView.setText(nam);
setContentView(textView);
//setContentView(R.layout.activity_display_message);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_display_message, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
下面是SQLHelperDatabase。
package com.doors.waynderful.myapp;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DatabaseHelper extends SQLiteOpenHelper
{
public static final String THE_DATABASE = "theDatabase";
public static final String THE_TABLE = "infoTable";
public static final String THE_TABLE_COLUMN_ID = "id";
public static final String THE_TABLE_COLUMN_NAME = "name";
public static final String THE_TABLE_COLUMN_DETAILS = "details";
DatabaseHelper(Context context)
{
super(context,THE_DATABASE, null, 1);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("create table " +THE_TABLE+"(id integer primary key, name text, details text) ");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("drop table if exists " + THE_TABLE + "");
onCreate(db);
}
public void addData(String nameIn, String detailsIn)
{
SQLiteDatabase db = this.getWritableDatabase();
ContentValues data = new ContentValues();
data.put("name", nameIn);
data.put("details", detailsIn);
db.insert(THE_TABLE,null,data);
}
public Cursor showData()
{
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor;
cursor = db.rawQuery("select * from "+THE_TABLE+"", null);
return cursor;
}
}
以下是MainActivity
package com.doors.waynderful.myapp;
import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;
public class MainActivity extends ActionBarActivity {
public final static String EXTRA_MESSAGE = "com.doors.waynderful.myapp.MESSAGE";
DatabaseHelper myDb;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public void sendMessage(View view){
myDb = new DatabaseHelper(this);
Intent intent = new Intent(this,DisplayMessageActivity.class);
EditText editText = (EditText) findViewById(R.id.edit_name);
EditText editText1 = (EditText) findViewById(R.id.edit_details);
String name = editText.getText().toString();
String details = editText1.getText().toString();
myDb.addData(name, details);
//intent.putExtra(EXTRA_MESSAGE,message);
startActivity(intent);
}
}
LOGCAT顯示
03-31 09:40:31.100 1351-1351 / com.doors.waynderful.myapp E / SQLiteLog:(1)沒有這樣的表:infoTable
我不確定為什么您認為必須在數據庫中必須有一個id為1的行
如果要查找具有特定名稱的行,請使用sql語句選擇具有該名稱的行。
如果要列出所有行,請選擇所有行。
但是插入一行,然后假設您知道它的id根本行不通。
另外,您應該使用使用布局的(當前已注釋掉)代碼,而不是創建新的文本視圖並將其設置為內容視圖。
最后,您似乎沒有任何代碼可以在數據庫中實際創建表?
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