Question

但有些不对劲，我是新的。我的代码

public class MainActivity extends AppCompatActivity {
    //kluci dla soedenenia
    public static final String APPI_ID = "----------------------";
    public static final String SECRET_KEY = "----------------";
    public static final String VERSION = "---";
    //moy log
    private static final String TAG = "myLogs";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //soedenil backendless
        Backendless.initApp(this, APPI_ID, SECRET_KEY, VERSION);

        Customer melinda = new Customer();
        melinda.setFirstName( "Melinda" );
        melinda.setLastName( "Grey" );
       Backendless.Persistence.of(Customer.class).save(melinda, new AsyncCallback<Customer>() {
           @Override
           public void handleResponse(Customer response) {

           }

           @Override
           public void handleFault(BackendlessFault fault) {

           }
       });
        System.out.println("Melinda's rate is "+melinda.getDiscountRatePercent()+"percent");
                melinda.setDiscountRatePercent( melinda.getDiscountRatePercent() + 2 );
        Backendless.Persistence.of(Customer.class).save(melinda, new AsyncCallback<Customer>() {
            @Override
            public void handleResponse(Customer customer) {

            }

            @Override
            public void handleFault(BackendlessFault fault) {

            }
        });
        Customer updatedMelinda = new Customer();
        updatedMelinda.setFirstName( "Melinda" );
        updatedMelinda.setLastName( "Grey" );

        updatedMelinda = Backendless.Persistence.of( Customer.class ).findById
                ( melinda.getID() );
        System.out.println("Now Melinda's discount rate is "+updatedMelinda.
                getDiscountRatePercent() +" percent.");

    }
        }

客户类

public class Customer {
    private String lastName;
    private Integer discountRatePercent;
    private String firstName;
    public String getLastName()
    {
        return lastName;
    }
    public void setLastName( String lastName )
    {
        this.lastName = lastName;
    }
    public Integer getDiscountRatePercent()
    {
        return discountRatePercent;
    }
    public void setDiscountRatePercent( Integer discountRatePercent )
    {
        this.discountRatePercent = discountRatePercent;
    }
    public String getFirstName()
    {
        return firstName;
    }
    public void setFirstName( String firstName )
    {
        this.firstName = firstName;
    }
}

我的java错误

10-22 03：14：23.620 2774-2774 /？ E / AndroidRuntime：致命异常：主要处理：com.example.elvir.subdexample，PID：2774 java.lang.RuntimeException：无法启动活动ComponentInfo {com.example.elvir.subdexample / com.example.elvir.subdexample.MainActivity}：java.lang.NullPointerException 在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2195）在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2245）在android.app.ActivityThread.access $ 800（ActivityThread.java:135）在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1196）在android.os.Handler.dispatchMessage（Handler.java:102）在android.os.Looper.loop（Looper.java:136）在android.app.ActivityThread.main（ActivityThread.java:5017） at java.lang.reflect.Method.invokeNative（Native Method）在java.lang.reflect.Method.invoke（Method.java:515）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:779）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:595） at dalvik.system.NativeStart.main（Native Method）引起：java.lang.NullPointerException at com.example.elvir.subdexample.MainActivity.onCreate（MainActivity.java:40）在android.app.Activity.performCreate（Activity.java:5231）在android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1087）在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2159）在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2245）在android.app.ActivityThread.access $ 800（ActivityThread.java:135）在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1196）在android.os.Handler.dispatchMessage（Handler.java:102）在android.os.Looper.loop（Looper.java:136）在android.app.ActivityThread.main（ActivityThread.java:5017） at java.lang.reflect.Method.invokeNative（Native Method）在java.lang.reflect.Method.invoke（Method.java:515）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:779）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:595）在dalvik.system.NativeStart.main（本地方法）

Answer 1

尝试替换

updatedMelinda = Backendless.Persistence.of( Customer.class ).findById
            ( updatedMelinda );

通过

updatedMelinda = Backendless.Persistence.of( Customer.class ).findById
            ( melinda.getID() );

什么是错的＆gt;？我不能做

1 个答案: