NullPointerException onCreate-Android微调器

Question

我在应用程序中遇到微调器。

旋转器应该将选定的项目传递到SQlite DB并保存数据。

但是到目前为止，每次我按下注册按钮时，它都会引发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

    }
}

我版式上的微调器：

<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>

然后是堆栈跟踪，它从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)

有任何想法吗？ 我浏览了一些示例，但仍然无法弄清楚

提前致谢！

编辑重复

不，重复并不能解决我的问题，因为此处涉及SQLite，这是一个简单的方法问题，谢谢。

第二编辑

这是btnJoin.setOnClickListener(new OnClickListener() {方法的样子，现在是同样的错误：

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

我认为您忘记了从视图中“查找”和膨胀小部件。 因此，当您调用txtName.getText（）。toString（）;时， 因为您的txtName仍然为null，所以它将引发nullPointerException。

为了解决这个问题，您需要先在代码中将所有小部件膨胀，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)

用于所有小部件。

编辑：您仍然收到相同的错误，因为您还没有膨胀按钮。

添加：

 btnJoin = (Button) findViewById(...)

在调用setOnClickListener之前。

Answer 2

您尚未为btnJoin分配任何值。 这导致了异常。

---

编辑1-如何解决问题

要解决此问题以及单击按钮时可能发生的其他问题，请在setContentView(R.layout.activity_members_register)之后setContentView(R.layout.activity_members_register)添加到onCreate（）方法中：

txtName = (EditText)findViewById(R.id.register_member_name);
txtPassword = (EditText)findViewById(R.id.register_member_password);
txtPasswordConf = (EditText)findViewById(R.id.register_member_password_confirm);
txtEmail = (EditText)findViewById(R.id.register_member_email);
txtEmailConf = (EditText)findViewById(R.id.register_member_email_confirm);
txtSchool = (EditText)findViewById(R.id.register_member_school);
btnJoin = (Button)findViewById(R.id.register_member_button_join);

只要您的布局文件中有以下内容：

...
<EditText android:id="@+id/register_member_name" ... />
...
<EditText android:id="@+id/register_member_password" ... />
...
<EditText android:id="@+id/register_member_password_confirm" ... />
...
<EditText android:id="@+id/register_member_email" ... />
...
<EditText android:id="@+id/register_member_email_confirm" ... />
...
<EditText android:id="@+id/register_member_school" ... />
...
<Button android:id="@+id/register_member_button_join" ... />
...

其中register_member_name ， register_member_password ， register_member_password_confirm ， register_member_email ， register_member_email_confirm ， register_member_school和register_member_button_join是小部件ID。 您不必完全使用这些名称。 只要您在布局文件和Java实现中使用相同的值，一切都会很好。

Answer 3

您应该在onClick方法中尝试

 spinner_school = (Spinner) findViewById(R.id.spinner_school);
  String school = spinner_school.getSelectedItem().toString();

并请在所有小部件中放入findviewByid

Answer 4

您的问题就在那里：

 Caused by: java.lang.NullPointerException
        at com.kkoci.shairlook.RegisterMember.onCreate(RegisterMember.java:57)

查看RegisterMember.java的第57行，您正在尝试访问一些尚未初始化的变量。 看不到行号，所以我无法进一步帮助您...这是您的第57行？