Question

我创建了一个从SQLite获取数据并在textview中显示的方法但是当按下按钮时显示应用程序崩溃。守则：

public void ViewData(){
    btnControler.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Cursor data = peopleDB.showData();
            if (data.getCount() == 0) {
                display("","");
                return;
            }
            StringBuffer buffer = new StringBuffer();
            StringBuffer buffer2 = new StringBuffer();
            while (data.moveToNext()) {
                display(buffer.append("Name:\t " + data.getString(1) + "\n").toString(),buffer2.append("Email:\t " + data.getString(2) + "\n").toString());

            }
        }
    });
}

public void display(String name, String email){
    TVusername.append(name);
    rphone.append(email);
}

错误被指定到第五行Cursor data = peopleDB.showData();

05-25 23:37:03.439 916-916/info.devexchanges.googlelocation E/AndroidRuntime: FATAL EXCEPTION: main
                                                                              Process: info.devexchanges.googlelocation, PID: 916
                                                                              java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.Cursor info.devexchanges.googlelocation.DatabaseHelper.showData()' on a null object reference
                                                                                  at info.devexchanges.googlelocation.LocationActivity$5.onClick(LocationActivity.java:473)
                                                                                  at android.view.View.performClick(View.java:5184)
                                                                                  at android.view.View$PerformClick.run(View.java:20910)
                                                                                  at android.os.Handler.handleCallback(Handler.java:739)
                                                                                  at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                  at android.os.Looper.loop(Looper.java:145)
                                                                                  at android.app.ActivityThread.main(ActivityThread.java:5951)
                                                                                  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:1400)
                                                                                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1195)

Answer 1

您可能缺少使用以下命令获取SQLiteDatabase引用：

DatabaseHelper databasehelper = new DatabaseHelper(getApplicationContext());
SQLiteDatabase peopleDB = databasehelper.getWritableDatabase();

您可以在this link中看到一个示例。

从SQLite获取数据

1 个答案: