NullPointerException：尝试在 null 对象引用上调用虚拟方法 'boolean java.lang.String.equalsIgnoreCase（java.lang.String）'

android java nullpointerexception

2022-09-01 15:00:45

我在运行时收到此错误。

java.lang.RuntimeException：无法启动活动 ComponentInfo java.lang.NullPointerException：尝试在 null 对象引用上调用虚拟方法 'boolean java.lang.String.equalsIgnoreCase（java.lang.String）'

堆栈跟踪：

01-12 03:44:54.270: E/AndroidRuntime(1437): FATAL EXCEPTION: main
01-12 03:44:54.270: E/AndroidRuntime(1437): Process: home.saket, PID: 1437
01-12 03:44:54.270: E/AndroidRuntime(1437): java.lang.RuntimeException: Unable to start activity ComponentInfo{home.saket/home.saket.addmember.Add_Update_User}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equalsIgnoreCase(java.lang.String)' on a null object reference
01-12 03:44:54.270: E/AndroidRuntime(1437):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
01-12 03:44:54.270: E/AndroidRuntime(1437):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
01-12 03:44:54.270: E/AndroidRuntime(1437):     at android.app.ActivityThread.access$800(ActivityThread.java:144)
01-12 03:44:54.270: E/AndroidRuntime(1437):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
01-12 03:44:54.270: E/AndroidRuntime(1437):     at android.os.Handler.dispatchMessage(Handler.java:102)
01-12 03:44:54.270: E/AndroidRuntime(1437):     at android.os.Looper.loop(Looper.java:135)
01-12 03:44:54.270: E/AndroidRuntime(1437):     at android.app.ActivityThread.main(ActivityThread.java:5221)
01-12 03:44:54.270: E/AndroidRuntime(1437):     at java.lang.reflect.Method.invoke(Native Method)
01-12 03:44:54.270: E/AndroidRuntime(1437):     at java.lang.reflect.Method.invoke(Method.java:372)
01-12 03:44:54.270: E/AndroidRuntime(1437):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
01-12 03:44:54.270: E/AndroidRuntime(1437):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
01-12 03:44:54.270: E/AndroidRuntime(1437): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equalsIgnoreCase(java.lang.String)' on a null object reference
01-12 03:44:54.270: E/AndroidRuntime(1437):     at home.saket.addmember.Add_Update_User.onCreate(Add_Update_User.java:38)
01-12 03:44:54.270: E/AndroidRuntime(1437):     at android.app.Activity.performCreate(Activity.java:5933)
01-12 03:44:54.270: E/AndroidRuntime(1437):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
01-12 03:44:54.270: E/AndroidRuntime(1437):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
01-12 03:44:54.270: E/AndroidRuntime(1437):     ... 10 more
01-12 03:44:54.272: W/ActivityManager(472):   Force finishing activity home.saket/.addmember.Add_Update_User
01-12 03:44:54.273: E/ActivityManager(472): Invalid thumbnail dimensions: 384x384

下面我张贴了代码并指出了错误行。

Add_Update_User.java：

@Override
    protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.add_update_screen);

    // set screen
    Set_Add_Update_Screen();

    // set visibility of view as per calling activity
    String called_from = getIntent().getStringExtra("called");

    if (called_from.equalsIgnoreCase("add")) {  --->38th error line
        add_view.setVisibility(View.VISIBLE);
        update_view.setVisibility(View.GONE);
    } else {

        update_view.setVisibility(View.VISIBLE);
        add_view.setVisibility(View.GONE);
        USER_ID = Integer.parseInt(getIntent().getStringExtra("USER_ID"));

        Contact c = dbHandler.Get_Contact(USER_ID);  

        add_name.setText(c.getName());
        add_mobile.setText(c.getPhoneNumber());
        add_email.setText(c.getEmail());
        // dbHandler.close();
    }
    }

答案 1

called_from必须为。针对该条件添加测试，例如null

if (called_from != null && called_from.equalsIgnoreCase("add")) {

或者你可以使用尤达条件（根据链接的维基百科文章中的优点，它也可以解决某些类型的不安全空行为，它们可以被描述为将表达式的常量部分放在条件语句的左侧。)

if ("add".equalsIgnoreCase(called_from)) { // <-- safe if called_from is null

答案 2

这是错误行：

if (called_from.equalsIgnoreCase("add")) {  --->38th error line

这意味着为空。在使用它之前，简单检查它是否为空：called_from

String called_from = getIntent().getStringExtra("called");

if (called_from != null && called_from.equalsIgnoreCase("add")) {
    // do whatever
} else {
    // do whatever
}

这样，如果为 null，它将执行条件的部分。called_fromelse