Java updateTextView（），显示当前用户android eclipse的名称

我对updateTextView有问题，比如当您登录到主活动时，它将转到下一个我命名为homepage/about的活动。有一个Welcome textview，它的右侧应该是当前用户的名称。与Welcome user类似

我尝试了updateTextView，但我有一个错误。请帮帮我

以下是homepage.java代码：

    package com.example.howtos;

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.database.Cursor;
//import android.database.Cursor;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;


public class homepage extends Activity {

private TextView textView;
private DatabaseManager dataBase;
public static final String TABLE_NAME = "users";
public static final String COLUMN_NAME = "real_name";

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.homepage);

  //get the connection on the 
    DatabaseManager dataBase = DatabaseManager.instance();

  //get the id of the textview to show text
    textView = (TextView) findViewById(R.id.textView2);

    Button a = (Button) findViewById (R.id.next1);
    a.setOnClickListener(new View.OnClickListener() {
        @Override    public void onClick(View v) {
     startActivity(new Intent(homepage.this,need.class)); 
        }
});
    Button out = (Button) findViewById (R.id.lo);
    out.setOnClickListener(new View.OnClickListener() {
        @Override    public void onClick(View v) {
     startActivity(new Intent(homepage.this,MainActivity.class)); 
     Toast.makeText(getApplicationContext(), "Logout Successful!", Toast.LENGTH_SHORT).show();

        }
    });


    updateTextView();   
}

    public void updateTextView() {

    //get all the available values from the database
        Cursor cursor = dataBase.select("SELECT real_name FROM " + TABLE_NAME);

        textView.setText("");

        while(cursor.moveToNext()) {

        //put the values fetched from the database to the textview
        String s = cursor.getString(cursor.getColumnIndex(COLUMN_NAME));
        textView.append("\n" + s);
        }


        cursor.close();
        //----->



    }  
}

还有我的日志：

    10-17 23:38:34.451: E/AndroidRuntime(644): FATAL EXCEPTION: main
10-17 23:38:34.451: E/AndroidRuntime(644): java.lang.RuntimeException: Unable to    start activity ComponentInfo{com.example.howtos/com.example.howtos.homepage}:   java.lang.NullPointerException
10-17 23:38:34.451: E/AndroidRuntime(644):  at  android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
10-17 23:38:34.451: E/AndroidRuntime(644):  at  android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
10-17 23:38:34.451: E/AndroidRuntime(644):  at android.app.ActivityThread.access    $600(ActivityThread.java:123)
10-17 23:38:34.451: E/AndroidRuntime(644):  at android.app.ActivityThread   $H.handleMessage(ActivityThread.java:1147)
10-17 23:38:34.451: E/AndroidRuntime(644):  at android.os.Handler.dispatchMessage   (Handler.java:99)
10-17 23:38:34.451: E/AndroidRuntime(644):  at android.os.Looper.loop   (Looper.java:137)
10-17 23:38:34.451: E/AndroidRuntime(644):  at android.app.ActivityThread.main  (ActivityThread.java:4424)
10-17 23:38:34.451: E/AndroidRuntime(644):  at  java.lang.reflect.Method.invokeNative(Native Method)
10-17 23:38:34.451: E/AndroidRuntime(644):  at java.lang.reflect.Method.invoke  (Method.java:511)
10-17 23:38:34.451: E/AndroidRuntime(644):  at com.android.internal.os.ZygoteInit   $MethodAndArgsCaller.run(ZygoteInit.java:784)
10-17 23:38:34.451: E/AndroidRuntime(644):  at  com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
10-17 23:38:34.451: E/AndroidRuntime(644):  at dalvik.system.NativeStart.main   (Native Method)
10-17 23:38:34.451: E/AndroidRuntime(644): Caused by: java.lang.NullPointerException
10-17 23:38:34.451: E/AndroidRuntime(644):  at  com.example.howtos.homepage.updateTextView(homepage.java:54)
10-17 23:38:34.451: E/AndroidRuntime(644):  at  com.example.howtos.homepage.onCreate(homepage.java:48)
10-17 23:38:34.451: E/AndroidRuntime(644):  at android.app.Activity.performCreate   (Activity.java:4465)
10-17 23:38:34.451: E/AndroidRuntime(644):  at  android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
10-17 23:38:34.451: E/AndroidRuntime(644):  at  android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
10-17 23:38:34.451: E/AndroidRuntime(644):  ... 11 more

---

在onCreate中，您将数据库重新定义为DataBaseManager，它在本地而不是全局定义数据库。换行

DatabaseManager dataBase = DatabaseManager.instance();

为此：

dataBase = DatabaseManager.instance();

---

非常感谢，先生但它显示了在数据库中注册的所有用户的名称。我可以让登录的用户只显示其名称吗？不是数据库中的所有名称。您必须在数据库查询中添加仅定义单个用户的内容，例如，从+TABLE\u name+中选择real\u name，其中id=+user\u id或类似内容谢谢，我会尝试解决这个问题。祝您好运！如果您对mysql查询不是非常熟悉，那么可以学习它们：