我有asyncTask,在DoInBackground方法內我調用一個DBHelper類,該類應該返回SQLiteDB中的每一行。但是,當DBHelper類方法來檢索值被炒魷魚我得到的錯誤:嘗試在空對象上調用虛擬方法參考
07-20 10:33:33.869: E/AndroidRuntime(22238): FATAL EXCEPTION: AsyncTask #5 07-20 10:33:33.869: E/AndroidRuntime(22238): Process: com.test.test, PID: 22238 07-20 10:33:33.869: E/AndroidRuntime(22238): java.lang.RuntimeException: An error occured while executing doInBackground() 07-20 10:33:33.869: E/AndroidRuntime(22238): at android.os.AsyncTask$3.done(AsyncTask.java:300) 07-20 10:33:33.869: E/AndroidRuntime(22238): at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355) 07-20 10:33:33.869: E/AndroidRuntime(22238): at java.util.concurrent.FutureTask.setException(FutureTask.java:222) 07-20 10:33:33.869: E/AndroidRuntime(22238): at java.util.concurrent.FutureTask.run(FutureTask.java:242) 07-20 10:33:33.869: E/AndroidRuntime(22238): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 07-20 10:33:33.869: E/AndroidRuntime(22238): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 07-20 10:33:33.869: E/AndroidRuntime(22238): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 07-20 10:33:33.869: E/AndroidRuntime(22238): at java.lang.Thread.run(Thread.java:818) 07-20 10:33:33.869: E/AndroidRuntime(22238): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void test.ItemFolderP.setId(java.lang.String)' on a null object reference 07-20 10:33:33.869: E/AndroidRuntime(22238): at test.test.returnValues(testt.java:59) 07-20 10:33:33.869: E/AndroidRuntime(22238): at test.test$GetFProducts.doInBackground(test.java:107) 07-20 10:33:33.869: E/AndroidRuntime(22238): at test.test$GetFProducts.doInBackground(test.java:1) 07-20 10:33:33.869: E/AndroidRuntime(22238): at android.os.AsyncTask$2.call(AsyncTask.java:288) 07-20 10:33:33.869: E/AndroidRuntime(22238): at java.util.concurrent.FutureTask.run(FutureTask.java:237) 07-20 10:33:33.869: E/AndroidRuntime(22238): ... 4 more
這是DBHelper的代碼:
public class DBHelper{
private ItemFolderP item; //here I declare my item
下面是檢索值
public ItemFolderP returnValues(int index){
Cursor mRow= database.rawQuery("select * from " + CM_TABLE + " LIMIT 0, 4", null);
if (null!=mRow) {
mRow.moveToNext();
item.setId(Integer.toString(mRow.getInt(mRow.getColumnIndex("Id"))));
item.setTitle(mRow.getString(mRow.getColumnIndex("test")));
item.setCode(mRow.getString(mRow.getColumnIndex("code")));
item.setPrice(mRow.getString(mRow.getColumnIndex("price")));
item.setImageUrl(mRow.getString(mRow.getColumnIndex("url")));
}
return item;
}
方法
這是商品分類:
public class ItemFolderP {
public String id;
public String title;
public String codice;
public String price;
public String imageUrl;
public ItemFolderP(String id, String title, String codice, String price, String imageUrl) {
super();
this.title = title;
this.id = id;
this.price = price;
this.imageUrl = imageUrl;
}
//titolo
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
//id
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
//codice
public String getCode() {
return title;
}
public void setCode(String codice) {
this.title = codice;
}
//image Url
public String getImageUrl() {
return imageUrl;
}
public void setImageUrl(String imageUrl) {
this.imageUrl = imageUrl;
}
//id
public String getPrice() {
return price;
}
public void setPrice(String price) {
this.price = price;
}
}
我覺得這個錯誤可能是由於我沒有將該上下文傳遞給該方法,但我無法理解如何解決它。有人能幫我嗎?
如果可能,請不要僅發佈錯誤消息,而是發佈完整的堆棧跟蹤。它也有助於您在* your *代碼中指出引起錯誤的行。對你而言問題:在從數據庫初始化的時候調用returnValues()函數到哪裏(因爲它看起來沒有正確初始化)? – dhke
@dhke我沒有發佈完整的DBHelper類代碼,因爲它與錯誤無關(代碼工作並且數據庫初始化正常),只要我調用Item.setId()方法就會發生錯誤。該方法在我的異步任務中調用DoInBackground方法 – Signo
@dhke我已經發布了完整的堆棧跟蹤! (我編輯了一些名字) – Signo