如何在增加/减少int值后将int值重置为0

Question

在我开始之前我想说我只是一个初学者，所以我希望你能理解我为什么要问这样一个问题简单的问题:)

随着“+”和“ - ”按钮，我调整数量。然后用“订单”按钮，我显示价格。但是当我按下“重新启动”按钮并再次调整数量时，数量不会从0开始，而是从最新数量开始。

这是XML：

<RelativeLayout 
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" 
tools:context=".MainActivity"> 

<TextView 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_margin="16dp" 
    android:textSize="16sp" 
    android:textAllCaps="true" 
    android:text="Quantity" 
    android:id="@+id/quantity" /> 

<Button 
    android:layout_width="48dp" 
    android:layout_height="48dp" 
    android:layout_marginLeft="16dp" 
    android:layout_marginBottom="16dp" 
    android:layout_below= "@id/quantity" 
    android:text="+" 
    android:id="@+id/increment" 
    android:onClick="increment" /> 

<TextView 
    android:layout_width="48dp" 
    android:layout_height="48dp" 
    android:layout_marginLeft="16dp" 
    android:layout_marginBottom="16dp" 
    android:layout_below= "@id/quantity" 
    android:layout_toRightOf = "@id/increment" 
    android:textSize="16sp" 
    android:textColor="#000000" 
    android:gravity="center" 
    android:text="0" 
    android:id="@+id/quantity_text_view" /> 

<Button 
    android:layout_width="48dp" 
    android:layout_height="48dp" 
    android:layout_marginLeft="16dp" 
    android:layout_marginBottom="16dp" 
    android:layout_below= "@id/quantity" 
    android:layout_toRightOf= "@id/quantity_text_view" 
    android:text="-" 
    android:id="@+id/decrement" 
    android:onClick="decrement" /> 

<TextView 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_marginLeft="16dp" 
    android:layout_marginBottom="16dp" 
    android:layout_below= "@id/increment" 
    android:textSize="16sp" 
    android:textAllCaps="true" 
    android:text="Price" 
    android:id="@+id/price" /> 

<TextView 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_marginLeft="16dp" 
    android:layout_marginBottom="16dp" 
    android:layout_below= "@id/price" 
    android:textSize="16sp" 
    android:textColor="#000000" 
    android:text="$0.00" 
    android:id="@+id/price_text_view" /> 

<Button 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_marginLeft="16dp" 
    android:layout_marginBottom="16dp" 
    android:layout_below= "@id/price_text_view" 
    android:text="Order" 
    android:id="@+id/button" 
    android:onClick="submitOrder" /> 

<TextView 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_below= "@id/button" 
    android:textSize="16sp" 
    android:text="" 
    android:id="@+id/enjoy" /> 

<Button 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_marginRight="16dp" 
    android:layout_marginBottom="16dp" 
    android:layout_alignParentBottom="true" 
    android:layout_alignParentRight="true" 
    android:text="Restart" 
    android:id="@+id/restart" 
    android:onClick="restart" /> 

</RelativeLayout> 

这里是在Java：

public class MainActivity extends ActionBarActivity { 

int quantity = 0; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    final Button button = (Button) findViewById(R.id.button); 
    button.setOnClickListener(new View.OnClickListener() { 
     public void onClick(View v) { 
      TextView view = (TextView) findViewById(R.id.enjoy); 
      view.setPadding(16, 0, 0, 16); 
      view.setText("Enjoy!"); 
      displayPrice(quantity * 5); 
     } 
    }); 
} 

/** 
* This method is called when the + button is clicked. 
*/ 
public void increment(View view){ 
    quantity = quantity + 1; 
    display(quantity); 
} 

/** 
* This method is called when the - button is clicked. 
*/ 
public void decrement(View view){ 
    quantity = quantity - 1; 
    display(quantity); 
} 

/** 
* This method is called when the order button is clicked. 
*/ 
public void submitOrder(View view) { 
    display(quantity); 

} 

/** 
* This method displays the given quantity value on the screen. 
*/ 
private void display(int number) { 
    TextView quantityTextView = (TextView) findViewById(
      R.id.quantity_text_view); 
      quantityTextView.setText("" + number); 
} 

/** 
* This method displays the given price on the screen. 
*/ 
private void displayPrice(int number) { 
    TextView priceTextView = (TextView) findViewById(R.id.price_text_view); 
    priceTextView.setText(NumberFormat.getCurrencyInstance().format(number)); 
} 

public void restart(View v) { 
    int quantity = 0; 
    display(quantity); 
    displayPrice(quantity); 
    TextView view = (TextView) findViewById(R.id.enjoy); 
    view.setPadding(0, 0, 0, 0); 
    view.setText(""); 
} 
} 

我想实现的是按下重启键，值了之后int quantity将重置为0.

Answer 1

在您正在创建的重启方法中一个名为quantity的新变量;但是，您应该使用已经为班级定义的数量。只需将方法更改为：

public void restart(View v) { 
    quantity = 0; 
    display(quantity); 
    displayPrice(quantity); 
    TextView view = (TextView) findViewById(R.id.enjoy); 
    view.setPadding(0, 0, 0, 0); 
    view.setText(""); 
} 

Answer 2

变量垫子的范围。您已在重新启动方法内声明了一个新变量，而不是使用已在MainActivity中声明的变量。

public void restart(View v) { 
    quantity = 0; 
    display(quantity); 
    displayPrice(quantity); 
    TextView view = (TextView) findViewById(R.id.enjoy); 
    view.setPadding(0, 0, 0, 0); 
    view.setText(""); 
}