致命異常，Java lang空指針異常

Question

我的以下代碼未顯示任何錯誤，但未執行。

package my.project.mil;

import android.content.Context;
import android.content.Intent;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class Cbdata extends MainActivity {

    public String str;

    public void onReceive(Context context, Intent intent) {
        //---get the CB message passed in---
        Bundle bundle = intent.getExtras();        
        SmsCbMessage[] msgs = null;
        str = "";            
        if (bundle != null)  {
            //---retrieve the SMS message received---
            Object[] pdus = (Object[]) bundle.get("pdus");
            msgs = new SmsCbMessage[pdus.length];            
            for (int i=0; i<msgs.length; i++) {
                msgs[i] = SmsCbMessage.createFromPdu((byte[])pdus[i]);                
                str += "CB " + msgs[i].getGeographicalScope() + msgs[i].getMessageCode() + msgs[i].getMessageIdentifier() + msgs[i].getUpdateNumber();                     
                str += " :";
                str += msgs[i].getMessageBody().toString();
                str += "\n";        
            }}
    }

    SQLiteDatabase cd = openOrCreateDatabase("MLIdb", MODE_WORLD_READABLE, null);



    Button submit;
Button viewdb;
EditText name;

@Override
    public void onCreate(Bundle savedInstanceState)
{
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.seventh);

    viewdb = (Button) findViewById(R.id.viewdb);
    submit = (Button) findViewById(R.id.submit);
    name = (EditText) findViewById(R.id.name);

    submit.setOnClickListener(new View.OnClickListener() 
    {

        public void onClick(View arg0) {

            String locname = name.getText().toString();
            if (locname.length()>0)
            {

                cd.execSQL("CREATE TABLE IF NOT EXITSTS MLITable (CblocationCode INT(10), CblocationName VARCHAR);");
                cd.execSQL("INSERT INTO MLITable VALUES (' ',' ');" +str +locname);
                Toast.makeText(getBaseContext(), "value successfully    entered.", Toast.LENGTH_LONG).show();
            }
            else
            {
                Toast.makeText(getBaseContext(), "Please enter the location name, for example 'Home'.", Toast.LENGTH_LONG).show();
            }

        }
    });

    cd.close();

    viewdb.setOnClickListener(new View.OnClickListener() 
    {

        public void onClick(View arg0) {
            // TODO Auto-generated method stub
            // here comes the code for viewing the database


        }
    });
}

}

而且我的錯誤日志如下所示，我還檢查了清單文件和MainActivity文件，但沒有遇到任何麻煩。

我的代碼應該收集用戶的基站塔區代碼，並通過用戶選擇名稱將其保存在數據庫中，該數據庫由兩個屬性組成，一個屬性是從用戶處收集的位置名稱，其次是基站的廣播塔信息。是從onReceive方法獲得的，單獨使用onReceive方法可以正常工作。

僅當我將數據庫集成到代碼中時，才會發生此問題。

謝謝。

Answer 1

SQLiteDatabase cd = openOrCreateDatabase("MLIdata", MODE_WORLD_WRITEABLE, null);

嘗試將其替換為

SQLiteDatabase cd = openOrCreateDatabase("MLIdata", MODE_WORLD_WRITEABLE);

Answer 2

我在上面的代碼中的錯誤，

1. 由於連接數據庫的方法錯誤，因此並非全部創建了cd。
2. 存在拼寫錯誤。
3. 插入方法錯誤。

最終正確的代碼是

public class Cbdata extends MainActivity {

    public String str;

    public void onReceive(Context context, Intent intent) {
        //---get the CB message passed in---
        Bundle bundle = intent.getExtras();        
        SmsCbMessage[] msgs = null;
        str = "";            
        if (bundle != null)  {
            //---retrieve the SMS message received---
            Object[] pdus = (Object[]) bundle.get("pdus");
            msgs = new SmsCbMessage[pdus.length];            
            for (int i=0; i<msgs.length; i++) {
                msgs[i] = SmsCbMessage.createFromPdu((byte[])pdus[i]);                
                str += "CB " + msgs[i].getGeographicalScope() + msgs[i].getMessageCode() + msgs[i].getMessageIdentifier() + msgs[i].getUpdateNumber();                     
                str += " :";
                str += msgs[i].getMessageBody().toString();
                str += "\n";        
            }}
}

Button submit;
Button viewdb;
EditText name;

@Override
public void onCreate(Bundle savedInstanceState)
{
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.seventh);



    viewdb = (Button) findViewById(R.id.viewdb);
    submit = (Button) findViewById(R.id.submit);
    name = (EditText) findViewById(R.id.name);

    submit.setOnClickListener(new View.OnClickListener() 
    {

        public void onClick(View arg0) {

            String locname = name.getText().toString();
            if (locname.length()>0)
            {
                SQLiteDatabase cd = openOrCreateDatabase("mydata", MODE_WORLD_READABLE, null);
                cd.execSQL("CREATE TABLE IF NOT EXISTS MLITable (CblocationCode INT(10), CblocationName VARCHAR);");
                cd.execSQL("INSERT INTO MLITable VALUES ('"+str+ "','"+locname+ "');");
                Toast.makeText(getBaseContext(), "value successfully entered.", Toast.LENGTH_LONG).show();
                cd.close();
            }
            else
            {
                Toast.makeText(getBaseContext(), "Please enter the location name, for example 'Home'.", Toast.LENGTH_LONG).show();
            }

        }
    });



    viewdb.setOnClickListener(new View.OnClickListener() 
    {

        public void onClick(View arg0) {
            // TODO Auto-generated method stub
            // here comes the code for viewing the database


        }
    });
}



}