java - 局部变量 NullPointerException

Question

当我单击 Login 类上的注册按钮时，出现 nullpointerException，它给出了该错误。我尝试修改本地和全局变量，但似乎没有任何方法可以修复该错误，我可能在 onClickListener 上混淆了，因为当我删除该代码时，它似乎可以工作。

注册.class。

public class Signup extends Activity {

    /*List Variables */ 
    private ScrollView scrollView1;

    private EditText editTextUN;

    private EditText editTextPW1;

    private EditText editTextPW2;

    private EditText editTextEMAIL;

    private Button buttonSignup;

    private Button buttonCancelSignup;



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

        /*set ContentView */
        setContentView(R.layout.signup);

        /*Populate fields */
        populate();


    }

    private void populate() {
        // TODO Auto-generated method stub

        /*initialize the ScrollView */
        ScrollView scrollView1 = (ScrollView) findViewById(R.id.scrollView1);

        /*initialize the EditText for the FIRST username field */
        final EditText editTextUN = (EditText) findViewById(R.id.editTextUN);

        /*initialize the FIRST password field */
        final EditText editTextPW1 = (EditText) findViewById(R.id.editTextPW1);

        /*initialize the SECOND password field */
        final EditText editTextPW2 = (EditText) findViewById(R.id.editTextPW2);

        /*initialize the signup Button */
        Button buttonSignup = (Button) findViewById(R.id.btsignup);

        /*initialize the cancel Button */
        Button buttonCancelSignup = (Button) findViewById(R.id.buttonCancelSignup);

        /*initialize the email EditText */
        final EditText editTextEMAIL = (EditText) findViewById(R.id.editTextEMAIL);

        /*setup OnClickListener */
        buttonSignup.setOnClickListener(new View.OnClickListener() {

            public void onClick(View v) {
                // TODO Auto-generated method stub

                /*check to see if it's the signup button */
                if(v.getId()== R.id.buttonSignup) {

                    /*get everything to a string */
                    String user = editTextUN.getText().toString();

                    String pass1 = editTextPW1.getText().toString();

                    String pass2 = editTextPW2.getText().toString();

                    String email = editTextEMAIL.getText().toString();


                    /*check to see if there's Text in all the Edit Text's */
                    if(user !=null && user.length()>5 && pass1.length()>5 && pass1 !=null && pass2.length()>5 && pass2 !=null && email.length()>5 && email !=null) {

                        /*send to comHelper */
                        ComHelper.sendSignUp(user, pass1, pass2, email);

                        while(ComHelper.sendSignUp(null, null, null, null)) {

                        }


                    }


                } else {
                    finish();
                }


            }
        });
    }





}

日志猫:

06-06 17:15:30.045: E/AndroidRuntime(1197): FATAL EXCEPTION: main
06-06 17:15:30.045: E/AndroidRuntime(1197): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.gta5news.qwuik/com.gta5news.qwuik.Signup}: java.lang.NullPointerException
06-06 17:15:30.045: E/AndroidRuntime(1197):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at android.app.ActivityThread.access$600(ActivityThread.java:123)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at android.os.Handler.dispatchMessage(Handler.java:99)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at android.os.Looper.loop(Looper.java:137)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at android.app.ActivityThread.main(ActivityThread.java:4424)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at java.lang.reflect.Method.invokeNative(Native Method)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at java.lang.reflect.Method.invoke(Method.java:511)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at dalvik.system.NativeStart.main(Native Method)
06-06 17:15:30.045: E/AndroidRuntime(1197): Caused by: java.lang.NullPointerException
06-06 17:15:30.045: E/AndroidRuntime(1197):     at com.gta5news.qwuik.Signup.populate(Signup.java:70)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at com.gta5news.qwuik.Signup.onCreate(Signup.java:40)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at android.app.Activity.performCreate(Activity.java:4465)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
06-06 17:15:30.045: E/AndroidRuntime(1197):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)

编辑:这是在 x86 模拟器上。

Answer 1

以上所有陈述都是正确的，但我认为 NullPointerException 的原因是:

as in Button buttonSignup = (Button) findViewById(R.id.btsignup); 右边的 id 是 R.id.buttonSignup

看起来buttonSignup在那里为空

正如您所使用的

................................................

/*检查是否是注册按钮*/

            if(v.getId()== `R.id.buttonSignup`) {

......................................................