Question

我的Activity应该显示用户的姓名和邮件地址（如果SharedPreferences中可用）。如果不是，则启动Dialog来向用户请求信息。

弹出Dialog，但是当单击“确定”按钮时，活动会抛出NullPointerException，其中包含以下日志，该日志指向else语句：

10-29 10:36:59.745: E/AndroidRuntime(16518): FATAL EXCEPTION: main
10-29 10:36:59.745: E/AndroidRuntime(16518): java.lang.NullPointerException
10-29 10:36:59.745: E/AndroidRuntime(16518):    at de.blubb.blubb.Blubb$1.onClick(Blubb.java:79)
10-29 10:36:59.745: E/AndroidRuntime(16518):    at com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:166)
10-29 10:36:59.745: E/AndroidRuntime(16518):    at android.os.Handler.dispatchMessage(Handler.java:99)
10-29 10:36:59.745: E/AndroidRuntime(16518):    at android.os.Looper.loop(Looper.java:137)
10-29 10:36:59.745: E/AndroidRuntime(16518):    at android.app.ActivityThread.main(ActivityThread.java:4759)
10-29 10:36:59.745: E/AndroidRuntime(16518):    at java.lang.reflect.Method.invokeNative(Native Method)
10-29 10:36:59.745: E/AndroidRuntime(16518):    at java.lang.reflect.Method.invoke(Method.java:511)
10-29 10:36:59.745: E/AndroidRuntime(16518):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
10-29 10:36:59.745: E/AndroidRuntime(16518):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:558)
10-29 10:36:59.745: E/AndroidRuntime(16518):    at dalvik.system.NativeStart.main(Native Method)

我的代码：

public class Blubb extends Activity {
public static final String username = "nameKey"; // for Shared Preferences
public static final String mailaddress = "mailKey"; // for Shared Preferences
public static final String BlubbPrefs = "preferences" ;
private static final int DIALOG_ALERT = 10; // constant for identifying the preference dialog

@Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    //addPreferencesFromResource(R.xml.preferences);
    setContentView(R.layout.activity_blubb);

    TextView viewUserName = (TextView) findViewById(R.id.viewUserNamen);
    TextView viewUserMail = (TextView) findViewById(R.id.viewMailAdresse);

    SharedPreferences settings = getSharedPreferences(BlubbPrefs, Context.MODE_PRIVATE);

    String name = settings.getString(username, "");
    String mail = settings.getString(mailaddress, "");

    /* Test if user settings are available */
    if ("".equals(name) || !"".equals(mail)) {
        System.out.println("Nutzerangaben fehlen");
/* Requesting user settings with a Dialog */        
        showDialog(DIALOG_ALERT);
        }
    if (settings.contains(username)){
        viewUserName.setText(settings.getString(username, ""));
       }
    if (settings.contains(mailaddress)){
        viewUserMail.setText(settings.getString(mailaddress, ""));
       }
}

public Dialog onCreateDialog(int id) {
    switch (id) {
    case DIALOG_ALERT:
     /* Create the new Dialog. */
        Context context = Blubb.this;
        AlertDialog.Builder builder = new AlertDialog.Builder(context);
        //Builder builder = new AlertDialog.Builder(this);
        LayoutInflater inflater = (LayoutInflater) this.getSystemService(LAYOUT_INFLATER_SERVICE);
        builder.setView(inflater.inflate(R.layout.dialog_settings, null));
        builder.setCancelable(false);

     /* OK-Button */    
        builder.setPositiveButton(R.string.button_send, new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int arg1) {                 
                final EditText editName = (EditText)findViewById(R.id.editUserNamen);
                final EditText editMail = (EditText)findViewById(R.id.editMailAdresse);

                /* Prove user settings */
                if (editName.getText().toString().trim().length() <= 0 ){
                    editName.setError("Name missing");
                    Toast.makeText(getApplicationContext(), "Name missing",  Toast.LENGTH_LONG).show();
                    //showAlertNameMissing();
                    }
                /*if (!inputMailAdresse.contains(".") || !inputMailAdresse.contains("@")) { */
                if (editMail.getText().toString().trim().contains(".") || editMail.getText().toString().trim().contains("@")){
                    editMail.setError("Mail incorrect");
                    Toast.makeText(getApplicationContext(), "Mail incorrect",  Toast.LENGTH_LONG).show();
                    //showAlertMailMissing();
                    }
                else {                      
                    final String inputUserNamen  = editName.getText().toString().trim();
                    final String inputMailAdresse = editMail.getText().toString().trim();
                    /* Reading access on preferences.xml */
                    SharedPreferences settings = getSharedPreferences(BlubbPrefs, Context.MODE_PRIVATE); // MODE_PRIVATE => can only be accessed by this application
                    /* Object of type editor to get writing access on preferences.xml */
                    SharedPreferences.Editor editor = settings.edit();
                    /* Saving key/value pairs to preferences.xml */
                    editor.putString(username, inputUserNamen);
                    editor.putString(mailaddress, inputMailAdresse); 
                    /* Writing key/value pairs to preferences.xml */
                    editor.commit();

                    Toast.makeText(getApplicationContext(), R.string.alert_saved, Toast.LENGTH_SHORT).show();
                    //return;
                    }                   
                dialog.dismiss();
                }
            }
        );
     /* Cancel-Button */        
        builder.setNegativeButton(R.string.button_cancel, new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int arg1) {
                dialog.dismiss();
                Toast.makeText(getApplicationContext(), "Input cancelled",  Toast.LENGTH_LONG).show();
                }
            });         

        AlertDialog dialog = builder.create();
        dialog.show();  
    }
    return super.onCreateDialog(id);
 }
}

作为编程的新手，当然还有Java，我一直试图通过搜索互联网并改变我的代码来寻找解决方案2周。但现在我很困惑。

解决了这个问题后，我还会遇到描述here的Dialog关闭问题吗？有人能帮助我吗？

Answer 1

空指针在编辑文本中最有可能。在您的代码的早期，您将相同的ID转换为textViews，现在您将它们转换为EditTexts，相同的布局对于两种不同类型的视图不能具有相同的ID。

TextView viewUserName = (TextView) findViewById(R.id.editUserNamen); //on your activity
EditText editName = (EditText)findViewById(R.id.editUserNamen); //on your dialog

这是最可能的错误。

单击“确定”按钮时，带有用户输入的AlertDialog显示NullPointerException

1 个答案: