Android SimpleCursorAdapter + ListView無法正常工作

Question

在線講座期間，我正在爲Android開發，在此時陷入困境。我寫了與講師完全相同的代碼，它從數據庫獲取一些數據並通過ListView將其顯示在屏幕上，但它沒有任何錯誤無法正常工作。

2個xml文件和1個java代碼如下。

雖然已經有人問問題，這個我無法找到合適的回答我的問題

命名方法「onButton4Clicked（）」可能是問題，但不知道這一點，所以我分享所有的東西在文件。

MainActivity.java

package org.androidtown.mydatabase; 

import android.content.Context; 
import android.database.Cursor; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteOpenHelper; 
import android.os.Bundle; 
import android.support.v4.widget.SimpleCursorAdapter; 
import android.support.v7.app.ActionBarActivity; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.widget.EditText; 
import android.widget.ListView; 
import android.widget.TextView; 
import android.widget.Toast; 


public class MainActivity extends ActionBarActivity { 
    EditText editText; EditText editText2; TextView textView; String databaseName; String tableName; 
    SQLiteDatabase database; 
    CustomerDatabaseHelper databaseHelper; 

    ListView listView; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     editText = (EditText) findViewById(R.id.editText); 
     editText2 = (EditText) findViewById(R.id.editText2); 
     textView = (TextView) findViewById(R.id.textView); 

     listView = (ListView) findViewById(R.id.listView); 
    } 

    public void onButton1Clicked(View v){ 
     databaseName = editText.getText().toString(); 
     try{ 
      databaseHelper = new CustomerDatabaseHelper(getApplicationContext(), databaseName, null, 2); 
      database = databaseHelper.getWritableDatabase(); 

      println("Database has been opened : " + databaseName); 
     } catch(Exception e){ 
      e.printStackTrace(); 
     } 
    } 

    public void onButton2Clicked(View v){ 
     //createTable(); 
    } 

    public void createTable(SQLiteDatabase db){ 
     tableName = editText2.getText().toString(); 
     try{ 
      if(db != null){ 
       db.execSQL("CREATE TABLE if not exists " + tableName + "(" 
         + "_id integer PRIMARY KEY autoincrement, " 
         + "name text, " 
         + "age integer, " 
         + "mobile text" 
         + ")"); 
       println("Table Created : " + tableName); 
      } else { 
       println("Should open Database first"); 
      } 
     } catch(Exception e){ 
      e.printStackTrace(); 
     } 
    } 

    public void changeTable(SQLiteDatabase db){ 
     try{ 
      if(db != null){ 
       db.execSQL("CREATE TABLE if not exists " + "PRODUCT" + "(" 
         + "_id integer PRIMARY KEY autoincrement, " 
         + "name text, " 
         + "price integer" 
         + ")"); 
       println("Add Additional Table : " + "PRODUCT"); 
      } else { 
       println("Should open Database first"); 
      } 
     } catch(Exception e){ 
      e.printStackTrace(); 
     } 
    } 

    public void onButton3Clicked(View v){ 
     try{ 
      if(tableName == null){ 
       tableName = editText2.getText().toString(); 
      } 

      if(database != null){ 
       database.execSQL("INSERT INTO " + tableName + "(name, age, mobile) VALUES " 
         + "('David', 20, '010-1000-1000')"); 

       println("Data has been added "); 
      } else { 
       println("Should open Database first"); 
      } 
     } catch(Exception e){ 
      e.printStackTrace(); 
     } 
    } 

    public void onButton4Clicked(View v){ 
     try{ 
      if(tableName == null){ 
       tableName = editText2.getText().toString(); 
      } 

      if(database != null){ 
       Cursor cursor = database.rawQuery("SELECT _id, name, age, mobile FROM " + tableName, null); 

       startManagingCursor(cursor); 

       String[] columns = new String[] {"name", "age", "mobile"}; 
       int[] to = new int[] {R.id.textView2, R.id.textView3, R.id.textView4}; 

       SimpleCursorAdapter adapter = new SimpleCursorAdapter(this, R.layout.customer_item, cursor, columns, to); 
       listView.setAdapter(adapter); 
       adapter.notifyDataSetChanged(); 

       int count = cursor.getCount(); 
       println("Counted Result Record : " + count); 

       for (int i = 0; i < count; i++){ 
        cursor.moveToNext(); 
        int _id = cursor.getInt(0); 
        String name = cursor.getString(1); 
        int age = cursor.getInt(2); 
        String mobile = cursor.getString(3); 

        println("Record #" + i + " : " + _id + name + ", " + age + ", " + mobile); 
       } 

       cursor.close(); 

       println("Inquired Data "); 
      } else { 
       println("Should open Database first"); 
      } 
     } catch(Exception e){ 
      e.printStackTrace(); 
     } 
    } 
    private void println(String data){ 
     textView.append(data + "\n"); 
    } 

    class CustomerDatabaseHelper extends SQLiteOpenHelper { 

     CustomerDatabaseHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) { 
      super(context, name, factory, version); 
     } 

     @Override 
     public void onOpen(SQLiteDatabase db) { 
      super.onOpen(db); 
      Toast.makeText(getApplicationContext(), "onOpen() in Helper has been called", Toast.LENGTH_LONG).show(); 
     } 

     @Override 
     public void onCreate(SQLiteDatabase db) { 
      Toast.makeText(getApplicationContext(), "onCreate() in Helper has been called", Toast.LENGTH_LONG).show(); 

      createTable(db); 
     } 

     @Override 
     public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
      Toast.makeText(getApplicationContext(), 
        "onUpgrade() in Helper has been called : " + oldVersion + "->" + newVersion, Toast.LENGTH_LONG).show(); 

      changeTable(db); 
     } 

    } 

    @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); 
    } 
} 

activity_main.xml中

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" 
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin" 
    android:paddingRight="@dimen/activity_horizontal_margin" 
    android:paddingTop="@dimen/activity_vertical_margin" 
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity" 
    android:orientation="vertical"> 

    <LinearLayout 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:orientation="horizontal"> 
     <EditText 
      android:layout_width="200dp" 
      android:layout_height="wrap_content" 
      android:id="@+id/editText" 
      android:text="customer.db" /> 
     <Button 
      android:layout_width="match_parent" 
      android:layout_height="wrap_content" 
      android:text="1. Open Database" 
      android:id="@+id/button" 
      android:onClick="onButton1Clicked" /> 
    </LinearLayout> 

    <LinearLayout 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:orientation="horizontal"> 
     <EditText 
      android:layout_width="200dp" 
      android:layout_height="wrap_content" 
      android:id="@+id/editText2" 
      android:text="customer" /> 
     <Button 
      android:layout_width="match_parent" 
      android:layout_height="wrap_content" 
      android:text="2. Create Table" 
      android:id="@+id/button2" 
      android:onClick="onButton2Clicked" /> 
    </LinearLayout> 

    <LinearLayout 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:orientation="horizontal"> 
     <Button 
      android:layout_width="match_parent" 
      android:layout_height="wrap_content" 
      android:text="3. Insert Data" 
      android:id="@+id/button3" 
      android:onClick="onButton3Clicked" /> 
    </LinearLayout> 

    <LinearLayout 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:orientation="horizontal"> 
     <Button 
      android:layout_width="match_parent" 
      android:layout_height="wrap_content" 
      android:text="4. Inquire Data" 
      android:id="@+id/button4" 
      android:onClick="onButton4Clicked" /> 
    </LinearLayout> 

    <ScrollView 
     android:layout_width="match_parent" 
     android:layout_height="100dp" 
     android:layout_below="@+id/button" 
     android:layout_alignParentLeft="true" 
     android:layout_alignParentStart="true" 
     android:layout_alignParentBottom="true" 
     android:layout_alignParentRight="true" 
     android:layout_alignParentEnd="true" 
     android:background="#aaff66"> 
     <TextView 
      android:layout_width="match_parent" 
      android:layout_height="match_parent" 
      android:id="@+id/textView"> 
     </TextView> 
    </ScrollView> 

    <ListView 
     android:layout_width="match_parent" 
     android:layout_height="match_parent" 
     android:id="@+id/listView" /> 


</LinearLayout> 

customer_item.xml

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:orientation="vertical" android:layout_width="match_parent" 
    android:layout_height="match_parent"> 

    <TextView 
     android:layout_width="228dp" 
     android:layout_height="wrap_content" 
     android:id="@+id/textView2" 
     android:textSize="30dp" /> 

    <TextView 
     android:layout_width="227dp" 
     android:layout_height="wrap_content" 
     android:id="@+id/textView3" 
     android:textSize="26dp" /> 

    <TextView 
     android:layout_width="213dp" 
     android:layout_height="wrap_content" 
     android:id="@+id/textView4" 
     android:textSize="20dp" 
     android:textColor="#ffff0000" /> 
</LinearLayout> 

Answer 1

你不應該關閉光標！

//cursor.close();