Java/Android NullPointerException on onClick

问题:

I have no idea why Android/Java is doing this, It's kind hard to think as I'm extremely tired and literally can't think for myself at this current time.

I'm creating static functions and imputing and executing the code that way, I don't think that's the reason as it hasn't even got past the if statement yet; what do you all think? I bet it's an easy solution, I just can't figure it out for the life of me.

Code:

public class LogIn extends Activity {
    Button login;
    EditText user;
    EditText pass;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.login);
        TextView top = (TextView) findViewById(R.id.textView2);
        EditText user = (EditText) findViewById(R.id.etUser);
        EditText pass = (EditText) findViewById(R.id.etPass);
        CheckBox stay = (CheckBox) findViewById(R.id.cBStay);
        Button login = (Button) findViewById(R.id.btLogin);
        Process();

   }

    private void Process() {
        // TODO Auto-generated method stub
    login.setOnClickListener( new View.OnClickListener() {

        public void onClick(View v) {
            // TODO Auto-generated method stub
            String user1 = user.getText().toString();
             String pass1 = pass.getText().toString();
            if(user1 !=null &user1.length()>=1 & pass1 !=null &pass1.length()>=1) {
                ComHelper.SendLogin(user1, pass1);
            }
        }
    });


    }



}

LogCat:

06-03 22:34:01.178: E/AndroidRuntime(2599): FATAL EXCEPTION: main
06-03 22:34:01.178: E/AndroidRuntime(2599): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.gta5news.qwuik/com.gta5news.qwuik.LogIn}: java.lang.NullPointerException
06-03 22:34:01.178: E/AndroidRuntime(2599):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
06-03 22:34:01.178: E/AndroidRuntime(2599):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
06-03 22:34:01.178: E/AndroidRuntime(2599):     at android.app.ActivityThread.access$600(ActivityThread.java:123)
06-03 22:34:01.178: E/AndroidRuntime(2599):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
06-03 22:34:01.178: E/AndroidRuntime(2599):     at android.os.Handler.dispatchMessage(Handler.java:99)
06-03 22:34:01.178: E/AndroidRuntime(2599):     at android.os.Looper.loop(Looper.java:137)
06-03 22:34:01.178: E/AndroidRuntime(2599):     at android.app.ActivityThread.main(ActivityThread.java:4424)
06-03 22:34:01.178: E/AndroidRuntime(2599):     at java.lang.reflect.Method.invokeNative(Native Method)
06-03 22:34:01.178: E/AndroidRuntime(2599):     at java.lang.reflect.Method.invoke(Method.java:511)
06-03 22:34:01.178: E/AndroidRuntime(2599):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
06-03 22:34:01.178: E/AndroidRuntime(2599):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
06-03 22:34:01.178: E/AndroidRuntime(2599):     at dalvik.system.NativeStart.main(Native Method)
06-03 22:34:01.178: E/AndroidRuntime(2599): Caused by: java.lang.NullPointerException
06-03 22:34:01.178: E/AndroidRuntime(2599):     at com.gta5news.qwuik.LogIn.Process(LogIn.java:32)
06-03 22:34:01.178: E/AndroidRuntime(2599):     at com.gta5news.qwuik.LogIn.onCreate(LogIn.java:26)
06-03 22:34:01.178: E/AndroidRuntime(2599):     at android.app.Activity.performCreate(Activity.java:4465)
06-03 22:34:01.178: E/AndroidRuntime(2599):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
06-03 22:34:01.178: E/AndroidRuntime(2599):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)

回答1:

I know this for a fact, but only because there is a single line in the Process() method.

Your instance member login has never been initialized, therefore, it is null, and thus, it throws a NullPointerException when you call the Process() method.

If you look in your onCreate() method, you are not saving your Button 'login' to the instance member, but instead to a local member.

login = (Button) findViewById(R.id.btLogin);

This should fix one problem, but you will have the same issue for the rest of your instance members too (at least user and pass).

user = (EditText) findViewById(R.id.etUser);
pass = (EditText) findViewById(R.id.etPass);