java - 按下后退按钮时，Android应用程序崩溃

当用户单击“后退”按钮时，我的应用程序崩溃了。

在我的应用中，我有3个相关 Activity :

MainActivity:显示人员列表

PersonActivity:显示一个人的所有付款的列表

AddPaymentActivity:具有输入元素以将付款添加到人员

在MainActivity中，用户可以点击列表中某个人员的姓名以转到PersonActivity，或者使用该人员姓名旁边的“+”按钮直接跳至AddPaymentActivity。在PersonActivity中，还有一个“+”按钮也可导致AddPaymentActivity。

Perons数据存储在实现Serializable接口(interface)的Java Person类中。启动 Activity 时，我通过以下方式转发人对象

intent.putExtra(MainActivity.PERSON_MESSAGE, person);

当我从MainActivity直接进入AddPaymentActivity(通过“+”)时，后退按钮可以正常工作。但是，如果我使用PersonActivity中的Start AddPaymentActivity启动，则我的应用程序崩溃，并出现空指针异常。

使用调试器，我注意到按下后退按钮时再次调用了PersonActivity.onCreate()？为什么从AddPaymentActivity返回到PersonActivity时会发生这种情况？从AddPaymentActivity返回MainActivity时为什么不发生这种情况？我该如何解决该问题？

堆栈跟踪:

01-13 10:11:01.423: E/AndroidRuntime(1022): FATAL EXCEPTION: main
01-13 10:11:01.423: E/AndroidRuntime(1022): Process: de.emteg.cashsplit, PID: 1022
01-13 10:11:01.423: E/AndroidRuntime(1022): java.lang.RuntimeException: Unable to start activity ComponentInfo{de.emteg.cashsplit/de.emteg.cashsplit.PersonActivity}: java.lang.NullPointerException
01-13 10:11:01.423: E/AndroidRuntime(1022):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2176)
01-13 10:11:01.423: E/AndroidRuntime(1022):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2226)
01-13 10:11:01.423: E/AndroidRuntime(1022):     at android.app.ActivityThread.access$700(ActivityThread.java:135)
01-13 10:11:01.423: E/AndroidRuntime(1022):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1397)
01-13 10:11:01.423: E/AndroidRuntime(1022):     at android.os.Handler.dispatchMessage(Handler.java:102)
01-13 10:11:01.423: E/AndroidRuntime(1022):     at android.os.Looper.loop(Looper.java:137)
01-13 10:11:01.423: E/AndroidRuntime(1022):     at android.app.ActivityThread.main(ActivityThread.java:4998)
01-13 10:11:01.423: E/AndroidRuntime(1022):     at java.lang.reflect.Method.invokeNative(Native Method)
01-13 10:11:01.423: E/AndroidRuntime(1022):     at java.lang.reflect.Method.invoke(Method.java:515)
01-13 10:11:01.423: E/AndroidRuntime(1022):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
01-13 10:11:01.423: E/AndroidRuntime(1022):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
01-13 10:11:01.423: E/AndroidRuntime(1022):     at dalvik.system.NativeStart.main(Native Method)
01-13 10:11:01.423: E/AndroidRuntime(1022): Caused by: java.lang.NullPointerException
01-13 10:11:01.423: E/AndroidRuntime(1022):     at java.math.BigDecimal.<init>(BigDecimal.java:425)
01-13 10:11:01.423: E/AndroidRuntime(1022):     at de.emteg.cashsplit.PersonActivity.onCreate(PersonActivity.java:37)
01-13 10:11:01.423: E/AndroidRuntime(1022):     at android.app.Activity.performCreate(Activity.java:5243)
01-13 10:11:01.423: E/AndroidRuntime(1022):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
01-13 10:11:01.423: E/AndroidRuntime(1022):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2140)
01-13 10:11:01.423: E/AndroidRuntime(1022):     ... 11 more

MainActivity.onCreate:

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_overview);

    persons = new ArrayList<Person>();

            // Populate list with some test person objects
    Person p = new Person("Frank");
    p.getPayments().add(new Payment("test1", new BigDecimal(5.7)));
    persons.add(p);

    p = new Person("Peter");
    persons.add(p);

    ListView list = (ListView) findViewById(R.id.listView1);
    PersonAdapter adapter = new PersonAdapter();
    list.setAdapter(adapter);
    // output....
}

PersonActivity.onCreate():

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_person);

    Intent intent = getIntent();
    this.person = (Person) intent.getSerializableExtra(MainActivity.PERSON_MESSAGE);
    this.share = new BigDecimal(intent.getStringExtra(MainActivity.SHARE_MESSAGE));
    this.totalSum = new BigDecimal(intent.getStringExtra(MainActivity.SUM_MESSAGE));
    this.diff = person.getSum().subtract(share);

    setupActionBar();

    // output...
}

AddPaymentActivty.onCreate():

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_add_payment);
    // Show the Up button in the action bar.
    setupActionBar();

    Intent intent = getIntent();

    this.person = (Person) intent.getSerializableExtra(MainActivity.PERSON_MESSAGE);

    if (intent.hasExtra(MainActivity.PAYMENT_MESSAGE)) {
        this.payment = (Payment) intent.getSerializableExtra(MainActivity.PAYMENT_MESSAGE);
        // output....
    } else {
        this.payment = null;
        // output...
    }

}

最佳答案

您的问题出在以下两行之一:

this.share = new BigDecimal(intent.getStringExtra(OverviewActivity.SHARE_MESSAGE));
this.totalSum = new BigDecimal(intent.getStringExtra(OverviewActivity.SUM_MESSAGE));

您的2个getStringExtra之一似乎返回null。

关于java - 按下后退按钮时，Android应用程序崩溃，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/21094347/