如何在增加/减少它的值后将 int 的值重置为 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么简单的问题:)

使用“+”和“-”按钮，我调整数量。然后使用“订单”按钮，我显示价格。但是当我按下“重启”按钮，然后再次调整数量时，数量不会从0开始，而是从最新的数量开始。

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 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("");
}
}

我想要实现的是，按下重启按钮后，intquantity的值会重置为0。

Answer 1

变量范围很重要。您已经在 restart 方法中声明了一个新变量，而不是使用您已经在 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("");
}

Answer 2

在您的重新启动方法中，您正在创建一个名为数量的新变量；但是，您应该使用已经为该类定义的数量。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("");
}