Question

当我尝试在数据库中添加信息时，应用停止。这是我存储项目信息的类（我在数据库中有3列）：

public class Elevator extends AppCompatActivity {
public int id ;
public String name;
public Date date;

//getters and setters here

public Elevator(int id, String name, Date date){
    setId(id);
    setName(name);
    setDate(date);
    DatabaseHelper myDB = new DatabaseHelper(this);
    myDB.addData(id,name,date);
}
}

我使用Button的主要活动是clickListener：

public class MainActivity extends AppCompatActivity {

DatabaseHelper myDB;
Button btnAdd;
EditText editText;

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

    btnAdd = (Button) findViewById(R.id.btnAdd);
    editText = (EditText) findViewById(R.id.editText);
    myDB = new DatabaseHelper(this);

    btnAdd.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
           String newEntry =  editText.getText().toString();
           int id =  myDB.getLastID();
            if (id == -1) {
                id=1;
                new  Elevator(id,newEntry,null);
            } else{
                new Elevator(id,newEntry,null);
            }
        }
    });
}
}

在构造函数中添加数据库中的信息是否正确，或者我应该以其他方式执行此操作？我的Elevator类是否应该扩展AppCompatActivity，如果它不能使用我的DatabaseHelperClass的实例。

这是logcat：

07-24 11:51:55.141: E/AndroidRuntime(5251): FATAL EXCEPTION: main
E/AndroidRuntime(5251): Process: com.example.goshoy.elevatorapp, PID: 5251
E/AndroidRuntime(5251): java.lang.NullPointerException: Attempt to invoke 
virtual method 'android.database.sqlite.SQLiteDatabase 
android.content.Context.openOrCreateDatabase(java.lang.String, int, 
android.database.sqlite.SQLiteDatabase$CursorFactory, 
android.database.DatabaseErrorHandler)' on a null object reference
E/AndroidRuntime(5251):     at 
android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:269)
E/AndroidRuntime(5251):     at 
android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked
(SQLiteOpenHelper.java:223)
E/AndroidRuntime(5251):     at 
android.database.sqlite.SQLiteOpenHelper.getWritableDatabase
(SQLiteOpenHelper.java:163)
E/AndroidRuntime(5251): at 
com.example.goshoy.elevatorapp.DatabaseHelper.addData
(DatabaseHelper.java:49)
E/AndroidRuntime(5251):     at com.example.goshoy.elevatorapp.Elevator.
<init>(Elevator.java:45)
E/AndroidRuntime(5251):     at 
com.example.goshoy.elevatorapp.MainActivity$1.onClick(MainActivity.java:34)
E/AndroidRuntime(5251):     at 
 android.view.View.performClick(View.java:5198)
E/AndroidRuntime(5251):     at 
 android.view.View$PerformClick.run(View.java:21147)
E/AndroidRuntime(5251):     at 
android.os.Handler.handleCallback(Handler.java:739)
E/AndroidRuntime(5251):     at 
android.os.Handler.dispatchMessage(Handler.java:95)
E/AndroidRuntime(5251):     at android.os.Looper.loop(Looper.java:148)
E/AndroidRuntime(5251):     at 
android.app.ActivityThread.main(ActivityThread.java:5417)
E/AndroidRuntime(5251):     at java.lang.reflect.Method.invoke(Native 
Method)
E/AndroidRuntime(5251):     at 
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run 
(ZygoteInit.java:726)
E/AndroidRuntime(5251):     at 
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

尝试在其中添加信息时，应用停止

0 个答案: