更新某个值并将其保存在离线数据库中

Question

我正在开发一个小型应用程序，该应用程序默认情况下将textview中的值设置为150,000。每个月我都会将该值重置为默认值。每次我花了一些金额，我打开我的应用程序，输入我花的金额和花了什么的细节。

我所做的是创建一个脱机数据库来存储我花了一些金额的所有时间，以及它的ID和细节。每次按“花费”按钮时，总金额都会减去我在EditText中输入的金额。

我还没有实现如何更新总量，我相信我必须使用一些名为sharedpreference的数字。

这是主要活动：

public class MainActivity extends AppCompatActivity { 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    Button spendMoney = (Button)this.findViewById(R.id.spendMoney); 
    Button test = (Button)this.findViewById(R.id.test); 
    TextView totalTxt = (TextView) this.findViewById(R.id.totalTxt); 
    final EditText spendAmount = (EditText)this.findViewById(R.id.spendAmount); 

    // int totalAmount = Integer.parseInt(totalTxt.getText().toString()); 

    final Paid_DB db = new Paid_DB(this); 



    spendMoney.setOnClickListener(new View.OnClickListener() { 

     @Override 

     public void onClick(View v) { 
      db.addPayment(new Payment(0, (Integer.parseInt(spendAmount.getText().toString())), "Test Details")); 

     } 

    }); 

    //totalAmount = totalAmount - Integer.parseInt(spendAmount.getText().toString()); 
    // totalTxt.setText(totalAmount); 
    test.setOnClickListener(new View.OnClickListener() { 

     @Override 

     public void onClick(View v) { 
      Intent i = new Intent(null, DetailsActivity.class); 
      startActivity(i); 
     } 

    }); 

XML文件：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:app="http://schemas.android.com/apk/res-auto" 
xmlns:tools="http://schemas.android.com/tools" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
tools:context="com.example.user.paid.MainActivity"> 

<TextView 
    android:id="@+id/textView3" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignParentLeft="true" 
    android:layout_alignParentStart="true" 
    android:layout_alignParentTop="true" 
    android:layout_marginLeft="13dp" 
    android:layout_marginStart="13dp" 
    android:layout_marginTop="53dp" 
    android:fontFamily="sans-serif" 
    android:text="Total:" 
    android:textSize="30sp" 
    tools:layout_editor_absoluteX="25dp" 
    tools:layout_editor_absoluteY="36dp" /> 

<EditText 
    android:id="@+id/spendAmount" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:ems="10" 
    android:inputType="number" 
    tools:layout_editor_absoluteX="72dp" 
    tools:layout_editor_absoluteY="143dp" 
    android:layout_marginBottom="38dp" 
    android:layout_above="@+id/spendMoney" 
    android:layout_centerHorizontal="true" /> 

<Button 
    android:id="@+id/spendMoney" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:text="Spend Money" 
    tools:layout_editor_absoluteX="115dp" 
    tools:layout_editor_absoluteY="215dp" 
    android:layout_centerVertical="true" 
    android:layout_centerHorizontal="true" /> 

<TextView 
    android:id="@+id/totalTxt" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignBaseline="@+id/textView3" 
    android:layout_alignBottom="@+id/textView3" 
    android:layout_alignEnd="@+id/spendMoney" 
    android:layout_alignRight="@+id/spendMoney" 
    android:fontFamily="sans-serif" 
    android:text="150,000" 
    android:textSize="30sp" 
    tools:layout_editor_absoluteX="25dp" 
    tools:layout_editor_absoluteY="36dp" /> 

<Button 
    android:id="@+id/test" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:text="Test" 
    tools:layout_editor_absoluteX="134dp" 
    tools:layout_editor_absoluteY="358dp" 
    android:layout_marginBottom="90dp" 
    android:layout_alignParentBottom="true" 
    android:layout_alignLeft="@+id/spendMoney" 
    android:layout_alignStart="@+id/spendMoney" /> 

这是我进入离线数据库，包含ID的对象时，花费金额，和付款细节：

public class Payment { 


private int id; 
private int amount; 
private String details; 


public Payment(){} 

public Payment(int id, int amount, String details) { 
    this.id = id; 
    this.amount = amount; 
    this.details = details; 
} 

public Payment(int id, int amount) { 
    this.id = id; 
    this.amount = amount; 
} 

public Payment(int amount, String details) { 
    this.amount = amount; 
    this.details = details; 
} 

public int getId() { 
    return id; 
} 

public void setId(int id) { 
    this.id = id; 
} 

public int getAmount() { 
    return amount; 
} 

public void setAmount(int amount) { 
    this.amount = amount; 
} 

public String getDetails() { 
    return details; 
} 

public void setDetails(String details) { 
    this.details = details; 
} } 

这是离线数据库：

ublic class Paid_DB extends SQLiteOpenHelper { 

// All Static variables 
// Database Version 
private static final int DATABASE_VERSION = 1; 

// Database Name 
private static final String DATABASE_NAME = "Payments_DB"; 

// Contacts table name 
private static final String PAYMENT_TABLE = "PaymentTable"; 

// Contacts Table Columns names 
private static final String PAY_ID = "id"; 
private static final String PAY_AMOUNT = "amount"; 
private static final String PAY_DETAILS = "details"; 

Paid_DB(Context context) { 
    super(context, DATABASE_NAME, null, DATABASE_VERSION); 
} 

@Override 
public void onCreate(SQLiteDatabase db) { 
    String CREATE_CONTACTS_TABLE = "CREATE TABLE " + PAYMENT_TABLE + "(" 
      + PAY_ID + " INTEGER PRIMARY KEY," + PAY_AMOUNT + " INTEGER," 
      + PAY_DETAILS + " TEXT" + ")"; 
    db.execSQL(CREATE_CONTACTS_TABLE); 
} 

@Override 
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 

    db.execSQL("DROP TABLE IF EXISTS " + PAYMENT_TABLE); 

    onCreate(db); 
} 

public void addPayment(Payment payment){ 

    SQLiteDatabase db = this.getWritableDatabase(); 

    ContentValues values = new ContentValues(); 
    values.put(PAY_AMOUNT, payment.getAmount()); 
    values.put(PAY_DETAILS, payment.getDetails()); // Contact Phone Number 

    // Inserting Row 
    db.insert(PAYMENT_TABLE, null, values); 
    db.close(); 
} 

void addListItem(ArrayList<String> listItem) { 
    SQLiteDatabase db = this.getWritableDatabase(); 

    ContentValues values = new ContentValues(); 
    for (int i = 0; i < listItem.size(); i++) { 

     Log.e("vlaue inserting==", "" + listItem.get(i)); 
     values.put(PAY_AMOUNT, listItem.get(i)); 
     db.insert(PAYMENT_TABLE, null, values); 

    } 

    db.close(); // Closing database connection 
} 

Cursor getListItem() { 
    String selectQuery = "SELECT * FROM " + PAYMENT_TABLE; 

    SQLiteDatabase db = this.getWritableDatabase(); 
    Cursor cursor = db.rawQuery(selectQuery, null); 

    return cursor; 
}} 

最后，这是细节的活动，它包含一个列表视图，存储并显示已取得的所有款项：

public class DetailsActivity extends AppCompatActivity { 

ArrayList<String> detailsListArrayList; 
private ListView lv; 

@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_details); 

    lv = (ListView) findViewById(R.id.listView); 
    detailsListArrayList = new ArrayList<>(); 

    detailsListArrayList.add("Item1"); 
    detailsListArrayList.add("Item2"); 
    detailsListArrayList.add("Item3"); 
    detailsListArrayList.add("Item4"); 
    detailsListArrayList.add("Item5"); 

    Paid_DB db = new Paid_DB(this); 

    db.addListItem(detailsListArrayList); 

    Cursor cursor = db.getListItem(); 

    Log.e("count", " " + cursor.getCount()); 
    if (cursor != null) { 
     cursor.moveToNext(); 

     do { 

      Log.e("value==", "" + cursor.getString(1)); 

     } while (cursor.moveToNext()); 
    } 

    ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(
      this, 
      android.R.layout.simple_list_item_1, 
      detailsListArrayList); 

    lv.setAdapter(arrayAdapter); 
} 
} 

XML文件：

<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:app="http://schemas.android.com/apk/res-auto" 
xmlns:tools="http://schemas.android.com/tools" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
tools:context="com.example.user.paid.DetailsActivity"> 

<ListView 
    android:id="@+id/listView" 
    android:layout_width="368dp" 
    android:layout_height="495dp" 
    tools:layout_editor_absoluteX="8dp" 
    tools:layout_editor_absoluteY="8dp" /> 

我每次点击“测试”按钮，应用程序崩溃。每当我尝试使用“花费”按钮添加新条目时，该应用也会崩溃。我做错了什么？

Answer 1

我可以告诉从这里（没有错误日志）是：按下测试按钮时

1）您的应用程序崩溃，因为你在那里开始的活动而没有经过context对象。试试这个：

public void onClick(View v) { 
     Intent i = new Intent(getApplicationContext(), DetailsActivity.class); 
     startActivity(i); 
    } 

2）花费按钮尝试添加一个新的支付条目到您的数据库。但在数据库模式中，您将PAY_ID声明为主键。稍后在您的addPayment()中，您只是传递PAY_AMOUNT和PAY_DETAILS，因此您错过了PAY_ID，这似乎导致崩溃。

编辑：这样的事情应该返回所有的支付作为一个ArrayList（可能包含错误，只是写在这个编辑器中）。

public ArrayList<Payment> getAllPayments() { 
     ArrayList<Payment> result = new ArrayList<>(); 
     Cursor c = db.query("PAYMENTS",new String[]{"PAY_ID","PAY_AMOUNT","PAY_DETAIL"},null,null,null,null,null); ; 

     c.moveToFirst(); 

     while(! c.isAfterLast()) 
     { 
      int s1=c.getInt(0); 
      int s2=c.getInt(1); 
      String s3=c.getString(2); 

      results.add(new Payment(s1,s2,s3)); 

      c.moveToNext(); 
     } 
     return results; 

}

要更新的ListView，你应该有一个仔细端详了这个链接，解释如何使用列表视图和一个自定义的ListView适配器Custom Adapter for List View