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我正在android应用程序中实现一个基本的CRUD函数。我通过我的注册创建了一个CREATE方法，并在我的登录中进行了读取。我没有收到我的注册错误，但当我登录我的应用程序崩溃，并在我的光标上生成空指针异常。光标指向null
我调用该方法searchRecord上登录按钮点击：
mLogin.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if(!mUsername.getText().toString().isEmpty() && !mPassword.getText().toString().isEmpty()) {
DBase db = new DBase(MainActivity.this);
if(db.searchRecord(mUsername.getText().toString(), mPassword.getText().toString())){
Toast.makeText(MainActivity.this, "Welcome, "+mUsername.getText().toString()+"!", Toast.LENGTH_LONG).show();
Intent intent = new Intent(MainActivity.this,TimeSetter.class);
startActivity(intent);
}
else {
Intent intent = new Intent(MainActivity.this,SignupActivity.class);
startActivity(intent);
}
}
}
});
这里是searchRecord方法在我的质数据库类：
public Boolean searchRecord(String username, String password) throws SQLException{
Boolean isUser = false;
String selectQuery = "SELECT * FROM "+DB_TABLE+" WHERE "+K_NAME+" = "+username+ " AND "+K_PASSWORD+" = "+password;
Cursor c = null;
c = dBase.rawQuery(selectQuery, null);
if(c.moveToFirst()){
isUser = false;
}
else {
isUser = false;
}
return isUser;
}
我实际上是基于上一个从获取记录功能单独的项目，我发现，因为我不熟悉SQLite：
public String[] getRecord(int rid) throws SQLException{
String selectQuery = "SELECT * FROM "+DB_TABLE+" WHERE "+K_RID+" = "+rid;
Cursor c = null;
c = dBase.rawQuery(selectQuery, null);
String[] data = new String[2];
if(c.moveToFirst()){
int indexName = c.getColumnIndex(K_NAME);
int indexCourse = c.getColumnIndex(K_EMAIL);
int indexPassword = c.getColumnIndex(K_PASSWORD);
data[0] = c.getString(indexName);
data[1] = c.getString(indexCourse);
data[2] = c.getString(indexPassword);
}
return data;
}
最后，这里是我的数据库声明：
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
db.execSQL(
"CREATE TABLE " + DB_TABLE + " (" +
K_RID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
K_NAME + " TEXT NOT NULL, " +
K_EMAIL + " TEXT NOT NULL, " +
K_PASSWORD + " TEXT NOT NULL);"
);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
db.execSQL("DROP TABLE IF EXIST " + DB_TABLE);
onCreate(db);
}
下面是我对错误日志：
02-25 22:33:22.261 21810-21810/com.exceptions.finalproject E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.exceptions.finalproject, PID: 21810
java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.Cursor android.database.sqlite.SQLiteDatabase.rawQuery(java.lang.String, java.lang.String[])' on a null object reference
at com.exceptions.finalproject.DBase.searchRecord(DBase.java:84)
at com.exceptions.finalproject.MainActivity$1$1.onClick(MainActivity.java:38)
at android.view.View.performClick(View.java:4848)
at android.view.View$PerformClick.run(View.java:20262)
at android.os.Handler.handleCallback(Handler.java:815)
at android.os.Handler.dispatchMessage(Handler.java:104)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5637)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:960)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
它指出，这条线：c = dBase.rawQuery(selectQuery, null);
谢谢！