将复选框状态从 XML 传递到 Java

Question

我是 android 开发的新手，我正在尝试使用 findViewById 方法传递复选框状态，但应用程序崩溃了：

这里是 xml 代码：

<CheckBox
        android:id="@+id/toppings_checkbox"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="16sp"
        android:layout_marginTop="8sp"
        android:layout_marginBottom="16sp"
        android:text="Whipped Cream"
        android:textColor="#FFFFFF"
        android:textSize="20sp"
        android:paddingLeft="16dp"
        android:buttonTint="#FFFFFF"
        />

这是 java 对 link 此复选框的声明 java:

public class MainActivity extends AppCompatActivity {
CheckBox hasWhippedCream = (CheckBox) findViewById(R.id.toppings_checkbox);
boolean checked = hasWhippedCream.isChecked();
int quantity = 0;
int pricePerCup = 5;
int toppingPrice = 0;

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

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

/**
 * This method is called when the - button is clicked
 */
public void Decrement(View view) {
    quantity = quantity - 1;
    if (quantity < 1) {
        quantity = 1;
    }
    displayQuantity(quantity);
}

/**
 * This method is called when the order button is clicked.
 */
public void submitOrder(View view) {
    displayMessage(createOrderSummary(calculatePrice()));
}

/**
 * Calculates the price of the order.
 */
private int calculatePrice() {

    if (checked = true) {
        toppingPrice = 2;
    } else {
        toppingPrice = 0;
    }
    return quantity * (pricePerCup + toppingPrice);
}

/**
 * This method displays summary of the given order.
 *
 * @param total is the total price of the order.
 *              * @return text summary
 */

private String createOrderSummary(int total) {

    String summary = "Name: Captain Samir\n";
    summary += "Add whipped cream? " + checked + "\n";
    summary += "Quantity: " + quantity + " Cups\n";
    summary += "Total: $" + total + "\n";
    summary += "Thank You!";
    return summary;
}

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

/**
 * This method displays the given text on the screen.
 */
private void displayMessage(String message) {
    TextView orderSummaryTextView = (TextView) findViewById(R.id.order_summary_text_view);
    orderSummaryTextView.setText(message);
}
}

然后我通过程序使用变量checked。知道为什么应用程序一旦启动就会崩溃吗？

Answer 1

试试这个：

public class MainActivity extends AppCompatActivity {
    CheckBox hasWhippedCream;
    boolean checked;
    int quantity = 0;
    int pricePerCup = 5;
    int toppingPrice = 0;

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

        hasWhippedCream = (CheckBox) findViewById(R.id.toppings_checkbox);
        hasWhippedCream.setOnCheckedChangeListener(new OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                checked = isChecked;
            }
        });
        checked = hasWhippedCream.isChecked();
    }

   // rest is the same
}

Answer 2

问题出在您的 Java 代码上。这是你犯的两个错误：

You were supposed to put your executable code inside your onCreate(), not outside of it.

You can only monitor for changes on your checkbox by calling onCheckedChangedListener() on it.

查看以下代码进行更正：

    public class MainActivity extends AppCompatActivity {


    boolean checked;


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

     CheckBox hasWhippedCream = (CheckBox) findViewById(R.id.toppings_checkbox);
     hasWhippedCream.setOnCheckedChangeListener(new OnCheckedChangeListener() {
           @Override
             public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
             checked = isChecked;
               }
                });


        int quantity = 0;
        int pricePerCup = 5;
        int toppingPrice = 0;

      }

     //Every other part of your code is correct ;-)

      }

希望对您有所帮助.. 编码愉快！！

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