NullPointerException：尝试在空对象引用上调用虚方法'boolean java.lang.String.equalsIgnoreCase（java.lang.String）' [英] NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equalsIgnoreCase(java.lang.String)' on a null object reference

问题描述

我在运行时收到此错误。

I am getting this error at runtime.

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

java.lang.RuntimeException: Unable to start activity ComponentInfo java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equalsIgnoreCase(java.lang.String)' on a null object reference

StackTrace：

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

下面我发布了代码并指出了错误行。

Below I am posted the codes and pointed out the error line.

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();
    }
    }

推荐答案

called_from 必须 null 。添加针对该条件的测试，例如

called_from must be null. Add a test against that condition like

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

或者您可以使用尤达条件（根据链接维基百科文章中的优势，它还可以解决某些类型的不安全 null 行为可以将它们描述为将表达式的常量部分放在条件语句的左侧）

or you could use Yoda conditions (per the Advantages in the linked Wikipedia article it can also solve some types of unsafe null behavior they can be described as placing the constant portion of the expression on the left side of the conditional statement)

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

这篇关于NullPointerException：尝试在空对象引用上调用虚方法'boolean java.lang.String.equalsIgnoreCase（java.lang.String）'的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！