java - NullPointerException onCreate - android spinner

Question

我的应用程序中的微调器遇到问题。

微调器应该将所选项目传递到 SQlite DB 并保存数据。

但到目前为止，每次我按下注册按钮时，它都会抛出 javaNullPointerException 错误。

这是我的课:

public class RegisterMember extends Activity implements OnItemSelectedListener{
DbAdapter dbAdapter;
EditText txtName;
EditText txtPassword;
EditText txtPasswordConf;
EditText txtEmail;
EditText txtEmailConf;
EditText txtSchool;
Button btnJoin;
//Button btnRegister;

private String[] state= {"USB","Stanford","Harvard","UCV","USM","Tor vergata", "La Sapienza"};
Spinner spinner_school;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_members_register);
    System.out.println(state.length);
    spinner_school = (Spinner) findViewById(R.id.spinner_school);
    ArrayAdapter<String> adapter_state = new ArrayAdapter<String>(this,
    android.R.layout.simple_spinner_item, state);
    adapter_state
    .setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    spinner_school.setAdapter(adapter_state);
    spinner_school.setOnItemSelectedListener(this);
    //btnRegister = (Button) findViewById(R.id.btn_reg);

    dbAdapter = new DbAdapter(this);
    dbAdapter.open();

    btnJoin.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View arg0) {
            InputMethodManager imm = (InputMethodManager) getSystemService(Context.INPUT_METHOD_SERVICE);
            imm.hideSoftInputFromWindow(txtName.getWindowToken(), 0);
            imm.hideSoftInputFromWindow(txtPassword.getWindowToken(), 0);
            imm.hideSoftInputFromWindow(txtPasswordConf.getWindowToken(), 0);
            imm.hideSoftInputFromWindow(txtEmail.getWindowToken(), 0);
            imm.hideSoftInputFromWindow(txtEmailConf.getWindowToken(), 0);
            //imm.hideSoftInputFromWindow(txtSchool.getWindowToken(), 0);
            //imm.hideSoftInputFromWindow(spinner_school.getWindowToken(), 0);
            try {

                String name = txtName.getText().toString();
                String password = txtPassword.getText().toString();
                String passwordconf = txtPasswordConf.getText().toString();
                String email = txtEmail.getText().toString();
                String emailconf = txtEmailConf.getText().toString();
                //String school = txtSchool.getText().toString();
                String school = spinner_school.getSelectedItem().toString();
                long i = dbAdapter.register(name, password, email, school);
                if(i != -1)
                    Toast.makeText(RegisterMember.this, "You have successfully registered",Toast.LENGTH_LONG).show();
                else {
                    if(!passwordconf.equals(password))
                    {
                        Toast.makeText(getApplicationContext(), "Password Does Not Matches", Toast.LENGTH_LONG).show();
                    }
                    if(!emailconf.equals(email))
                    {
                        Toast.makeText(getApplicationContext(), "Email Does Not Matches", Toast.LENGTH_LONG).show();
                    }

                }

            } catch (SQLException e) {
                Toast.makeText(RegisterMember.this, "Some problem occurred",
                        Toast.LENGTH_LONG).show();

            }

        }
    });
}
public void onItemSelected(AdapterView<?> parent, View view, int position,
                           long id) {
    spinner_school.setSelection(position);
}
@Override
public void onNothingSelected(AdapterView<?> arg0) {
    // TODO Auto-generated method stub

    }
}

布局上的微调器:

<TableRow
        android:id="@+id/tableRow10"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" >

        <Spinner
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/spinner_school"
            android:spinnerMode="dropdown" />

    </TableRow>

堆栈跟踪，它从方法 btnJoin.setOnClickListener(new OnClickListener()

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.shairlook/com.kkoci.shairlook.RegisterMember}: java.lang.NullPointerException
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2245)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2295)
        at android.app.ActivityThread.access$700(ActivityThread.java:150)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1280)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:175)
        at android.app.ActivityThread.main(ActivityThread.java:5279)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:511)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
        at dalvik.system.NativeStart.main(Native Method)
 Caused by: java.lang.NullPointerException
        at com.kkoci.shairlook.RegisterMember.onCreate(RegisterMember.java:57)

有什么想法吗？我已经查看了示例，但仍然无法弄清楚这一点

提前致谢!

编辑重复内容

不，重复并不能解决我的问题，因为这里涉及到SQLite，这是一个简单的方法问题，谢谢。

第二次编辑

这就是 btnJoin.setOnClickListener(new OnClickListener() { 方法现在的样子，同样的错误:

btnJoin.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View arg0) {
            InputMethodManager imm = (InputMethodManager) getSystemService(Context.INPUT_METHOD_SERVICE);
            imm.hideSoftInputFromWindow(txtName.getWindowToken(), 0);
            imm.hideSoftInputFromWindow(txtPassword.getWindowToken(), 0);
            imm.hideSoftInputFromWindow(txtPasswordConf.getWindowToken(), 0);
            imm.hideSoftInputFromWindow(txtEmail.getWindowToken(), 0);
            imm.hideSoftInputFromWindow(txtEmailConf.getWindowToken(), 0);
            //imm.hideSoftInputFromWindow(txtSchool.getWindowToken(), 0);
            //imm.hideSoftInputFromWindow(spinner_school.getWindowToken(), 0);
            try {

                txtName = (EditText) findViewById(R.id.et_user);
                String name = txtName.getText().toString();
                txtPassword = (EditText) findViewById(R.id.et_pw_reg);
                String password = txtPassword.getText().toString();
                txtPasswordConf = (EditText) findViewById(R.id.et_pw_conf);
                String passwordconf = txtPasswordConf.getText().toString();
                txtEmail = (EditText) findViewById(R.id.et_email_reg);
                String email = txtEmail.getText().toString();
                txtEmailConf = (EditText) findViewById(R.id.et_email_conf);
                String emailconf = txtEmailConf.getText().toString();
                //String school = txtSchool.getText().toString();
                spinner_school = (Spinner) findViewById(R.id.spinner_school);
                String school = spinner_school.getSelectedItem().toString();
                long i = dbAdapter.register(name, password, email, school);
                if(i != -1)
                    Toast.makeText(RegisterMember.this, "You have successfully registered",Toast.LENGTH_LONG).show();
                else {
                    if(!passwordconf.equals(password))
                    {
                        Toast.makeText(getApplicationContext(), "Password Does Not Matches", Toast.LENGTH_LONG).show();
                    }
                    if(!emailconf.equals(email))
                    {
                        Toast.makeText(getApplicationContext(), "Email Does Not Matches", Toast.LENGTH_LONG).show();
                    }

                }

            } catch (SQLException e) {
                Toast.makeText(RegisterMember.this, "Some problem occurred",
                        Toast.LENGTH_LONG).show();

            }

        }
    });

Answer 1

我认为您忘记了从您的 View 中“查找”并膨胀小部件。因此，当你打电话时 txtName.getText().toString();它抛出 nullPointerException 因为你的 txtName 仍然为空。

要解决此问题，您需要先膨胀代码中的所有小部件，然后再尝试访问它们。因此，在调用 setContentView() 之后，您将执行以下操作:

txtName = (EditText) findViewById(R.id.the_id_of_the_widget)

适用于您的所有小部件。

编辑:您仍然收到相同的错误，因为您仍然没有膨胀按钮。

添加:

 btnJoin = (Button) findViewById(...)

在调用 setOnClickListener 之前。