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如何檢查對象關係是否爲空？

2014-12-06 82 views
2 
ParseObject current; 
... 
ParseQuery<ParseObject> query = ParseQuery.getQuery("Primary"); 
    try{ 
     if(current == null){ 
      System.out.println("current is NULL");     //prints properly 
      System.out.println("Initial query: " + query.count()); //prints 'Initial Query: 90' 
      query.whereDoesNotExist("Parent4"); 
      System.out.println("Test1");        //prints properly 
      System.out.println("Query Count: " + query.count());  //seems to cause nullpointer 
      List<ParseObject> list = query.find(); 
      System.out.println("Test2"); 
      for(ParseObject p: list){ 
       listItems.add((String)p.get("Title")); //listItems used to populate listview when listview is generated 

...(closing brackets,else statement, exception catching, rest of program)

我試圖搜索我的解析數據庫標題爲「主要」的所有在「Parent4」（關係）字段中具有空關係的項目，並將它們顯示到我的字符串列表（listItems）中添加到listView創建時。我知道我的數據庫中的兩個對象沒有任何關係，所以我希望顯示這兩個對象的標題。我之前有一個有點工作的版本之前，這工作得很好，除了我檢查列表中的每個對象的標題，而不是對象本身導致後來在我的程序中，當兩個對象具有相同的標題，這是什麼這在我的程序中應該是可以接受的。如何檢查對象關係是否爲空？

任何想法爲什麼行「query.whereDoesNotExist（」Parent4「）;」當我想要打印查詢的計數時，似乎導致空指針異常？或者任何想法，我可以如何處理這個呢？

這裏的日誌：

12-06 18:20:50.030: I/Process(2469): Sending signal. PID: 2469 SIG: 9 
12-06 18:20:57.740: I/System.out(2517): current is NULL 
12-06 18:20:58.159: I/System.out(2517): Initial query: 92 
12-06 18:20:58.159: I/System.out(2517): Test1 
12-06 18:20:58.378: D/AndroidRuntime(2517): Shutting down VM 
12-06 18:20:58.379: E/AndroidRuntime(2517): FATAL EXCEPTION: main 
12-06 18:20:58.379: E/AndroidRuntime(2517): Process: com.parse.starter, PID: 2517 
12-06 18:20:58.379: E/AndroidRuntime(2517): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.parse.starter/com.parse.starter.ParseStarterProjectActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'int org.json.JSONObject.optInt(java.lang.String)' on a null object reference 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at android.app.ActivityThread.access$800(ActivityThread.java:144) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at android.os.Handler.dispatchMessage(Handler.java:102) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at android.os.Looper.loop(Looper.java:135) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at android.app.ActivityThread.main(ActivityThread.java:5221) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at java.lang.reflect.Method.invoke(Native Method) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at java.lang.reflect.Method.invoke(Method.java:372) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694) 
12-06 18:20:58.379: E/AndroidRuntime(2517): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int org.json.JSONObject.optInt(java.lang.String)' on a null object reference 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at com.parse.ParseQuery$18.then(ParseQuery.java:1014) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at com.parse.ParseQuery$18.then(ParseQuery.java:1011) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$9.run(Task.java:444) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.BoltsExecutors$ImmediateExecutor.execute(BoltsExecutors.java:97) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.completeImmediately(Task.java:440) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.access$100(Task.java:27) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$5.then(Task.java:307) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$5.then(Task.java:304) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.runContinuations(Task.java:506) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.access$600(Task.java:27) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$TaskCompletionSource.trySetError(Task.java:577) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$TaskCompletionSource.setError(Task.java:604) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$10$1.then(Task.java:487) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$10$1.then(Task.java:481) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$9.run(Task.java:444) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.BoltsExecutors$ImmediateExecutor.execute(BoltsExecutors.java:97) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.completeImmediately(Task.java:440) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.continueWith(Task.java:314) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.continueWith(Task.java:325) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$10.run(Task.java:481) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.BoltsExecutors$ImmediateExecutor.execute(BoltsExecutors.java:97) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.completeAfterTask(Task.java:473) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.access$200(Task.java:27) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$6.then(Task.java:342) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$6.then(Task.java:339) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.runContinuations(Task.java:506) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.access$600(Task.java:27) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$TaskCompletionSource.trySetError(Task.java:577) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at com.parse.ParseRequest$4.then(ParseRequest.java:350) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at com.parse.ParseRequest$4.then(ParseRequest.java:344) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$10.run(Task.java:477) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.BoltsExecutors$ImmediateExecutor.execute(BoltsExecutors.java:97) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.completeAfterTask(Task.java:473) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.access$200(Task.java:27) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$6.then(Task.java:342) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$6.then(Task.java:339) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.runContinuations(Task.java:506) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.access$600(Task.java:27) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$TaskCompletionSource.trySetError(Task.java:577) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$TaskCompletionSource.setError(Task.java:604) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$10$1.then(Task.java:487) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$10$1.then(Task.java:481) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$9.run(Task.java:444) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.BoltsExecutors$ImmediateExecutor.execute(BoltsExecutors.java:97) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.completeImmediately(Task.java:440) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.continueWith(Task.java:314) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.continueWith(Task.java:325) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$10.run(Task.java:481) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.BoltsExecutors$ImmediateExecutor.execute(BoltsExecutors.java:97) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.completeAfterTask(Task.java:473) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.access$200(Task.java:27) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$6.then(Task.java:342) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$6.then(Task.java:339) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.runContinuations(Task.java:506) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task.access$600(Task.java:27) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$TaskCompletionSource.trySetResult(Task.java:561) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$TaskCompletionSource.setResult(Task.java:595) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$10$1.then(Task.java:489) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$10$1.then(Task.java:481) 
12-06 18:20:58.379: E/AndroidRuntime(2517):  at bolts.Task$9.ru 
12-06 18:20:58.379: D/Error(2517): ERR: exClass=java.lang.NullPointerException 
12-06 18:20:58.379: D/Error(2517): ERR: exMsg=Attempt to invoke virtual method 'int org.json.JSONObject.optInt(java.lang.String)' on a null object reference 
12-06 18:20:58.379: D/Error(2517): ERR: file=ParseQuery.java 
12-06 18:20:58.379: D/Error(2517): ERR: class=com.parse.ParseQuery$18 
12-06 18:20:58.379: D/Error(2517): ERR: method=then line=1014 
12-06 18:20:58.379: D/Error(2517): ERR: stack=java.lang.RuntimeException: Unable to start activity ComponentInfo{com.parse.starter/com.parse.starter.ParseStarterProjectActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'int org.json.JSONObject.optInt(java.lang.String)' on a null object reference 
12-06 18:20:58.379: D/Error(2517): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298) 
12-06 18:20:58.379: D/Error(2517): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360) 
12-06 18:20:58.379: D/Error(2517): at android.app.ActivityThread.access$800(ActivityThread.java:144) 
12-06 18:20:58.379: D/Error(2517): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278) 
12-06 18:20:58.379: D/Error(2517): at android.os.Handler.dispatchMessage(Handler.java:102) 
12-06 18:20:58.379: D/Error(2517): at android.os.Looper.loop(Looper.java:135) 
12-06 18:20:58.379: D/Error(2517): at android.app.ActivityThread.main(ActivityThread.java:5221) 
12-06 18:20:58.379: D/Error(2517): at java.lang.reflect.Method.invoke(Native Method) 
12-06 18:20:58.379: D/Error(2517): at java.lang.reflect.Method.invoke(Method.java:372) 
12-06 18:20:58.379: D/Error(2517): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899) 
12-06 18:20:58.379: D/Error(2517): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694) 
12-06 18:20:58.379: D/Error(2517): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int org.json.JSONObject.optInt(java.lang.String)' on a null object reference 
12-06 18:20:58.379: D/Error(2517): at com.parse.ParseQuery$18.then(ParseQuery.java:1014) 
12-06 18:20:58.379: D/Error(2517): at com.parse.ParseQuery$18.then(ParseQuery.java:1011) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$9.run(Task.java:444) 
12-06 18:20:58.379: D/Error(2517): at bolts.BoltsExecutors$ImmediateExecutor.execute(BoltsExecutors.java:97) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.completeImmediately(Task.java:440) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.access$100(Task.java:27) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$5.then(Task.java:307) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$5.then(Task.java:304) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.runContinuations(Task.java:506) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.access$600(Task.java:27) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$TaskCompletionSource.trySetError(Task.java:577) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$TaskCompletionSource.setError(Task.java:604) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$10$1.then(Task.java:487) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$10$1.then(Task.java:481) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$9.run(Task.java:444) 
12-06 18:20:58.379: D/Error(2517): at bolts.BoltsExecutors$ImmediateExecutor.execute(BoltsExecutors.java:97) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.completeImmediately(Task.java:440) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.continueWith(Task.java:314) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.continueWith(Task.java:325) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$10.run(Task.java:481) 
12-06 18:20:58.379: D/Error(2517): at bolts.BoltsExecutors$ImmediateExecutor.execute(BoltsExecutors.java:97) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.completeAfterTask(Task.java:473) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.access$200(Task.java:27) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$6.then(Task.java:342) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$6.then(Task.java:339) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.runContinuations(Task.java:506) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.access$600(Task.java:27) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$TaskCompletionSource.trySetError(Task.java:577) 
12-06 18:20:58.379: D/Error(2517): at com.parse.ParseRequest$4.then(ParseRequest.java:350) 
12-06 18:20:58.379: D/Error(2517): at com.parse.ParseRequest$4.then(ParseRequest.java:344) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$10.run(Task.java:477) 
12-06 18:20:58.379: D/Error(2517): at bolts.BoltsExecutors$ImmediateExecutor.execute(BoltsExecutors.java:97) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.completeAfterTask(Task.java:473) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.access$200(Task.java:27) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$6.then(Task.java:342) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$6.then(Task.java:339) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.runContinuations(Task.java:506) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.access$600(Task.java:27) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$TaskCompletionSource.trySetError(Task.java:577) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$TaskCompletionSource.setError(Task.java:604) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$10$1.then(Task.java:487) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$10$1.then(Task.java:481) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$9.run(Task.java:444) 
12-06 18:20:58.379: D/Error(2517): at bolts.BoltsExecutors$ImmediateExecutor.execute(BoltsExecutors.java:97) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.completeImmediately(Task.java:440) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.continueWith(Task.java:314) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.continueWith(Task.java:325) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$10.run(Task.java:481) 
12-06 18:20:58.379: D/Error(2517): at bolts.BoltsExecutors$ImmediateExecutor.execute(BoltsExecutors.java:97) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.completeAfterTask(Task.java:473) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.access$200(Task.java:27) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$6.then(Task.java:342) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$6.then(Task.java:339) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.runContinuations(Task.java:506) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task.access$600(Task.java:27) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$TaskCompletionSource.trySetResult(Task.java:561) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$TaskCompletionSource.setResult(Task.java:595) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$10$1.then(Task.java:489) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$10$1.then(Task.java:481) 
12-06 18:20:58.379: D/Error(2517): at bolts.Task$9.run(Task.java:444) 
12-06 18:20:58.379: D/Error(2517): at bolts.BoltsExecutors$ImmediateExecuto 
12-06 18:20:58.379: D/Error(2517): ERR: TOTAL BYTES WRITTEN: 13252

來源

2014-12-06 user4333097

+0

問：你能澄清你所說的 「query.whereDoesNotExist（」 Parent4" ）的意思; 「當我想要打印查詢的計數時，似乎導致空指針異常？ 「在哪一行是被調用的異常？'whereDoesNotExist'或'count（）'後面的 – cjds 2014-12-07 00:08:25

+0

不幸的是我不確定。我的eclipse日誌似乎並沒有說12-06 18：09：41.636：D/AndroidRuntime （2121）：---------開始崩潰 12-06 18：09：41.659：E/AndroidRuntime（2121）：致命例外：主要 12-06 18：09：41.659：E/AndroidRuntime （2121）：進程：com.parse.starter，PID：2121 12-06 18：09：41.659：E/AndroidRuntime（2121）：java.lang.RuntimeException：無法啓動活動ComponentInfo {com.parse.starter/com.parse.starter.ParseStarterProjectActivity}：java.lang.NullPointerException：嘗試在空對象引用 – user4333097 2014-12-07 00:13:31

+0

上調用虛擬方法'int org.json.JSONObject.optInt（java.lang.String）'您是否也可以發佈錯誤日誌？ – cjds 2014-12-07 00:15:38

回答

1

更新時間： 你可以做到這一點通過另一個方法

ParseQuery<RelationParse> innerQuery = ParseQuery.getQuery("Primary"); 
ParseQuery<TestParse> query = ParseQuery.getQuery("Primary"); 
query.whereDoesNotMatchQuery("Parent4", innerQuery); 
List<TestParse> listWithEmptyRelations = query.find();

來源

2014-12-07 08:22:36 gio

+0

Parent4在Primary類中，它是指主類，所以我不認爲at'll工作。還有像這樣的簡單解決方案嗎？ – user4333097 2014-12-07 19:40:41

+0

然後，您還需要在內部查詢中使用「主要」。 – gio 2014-12-07 21:48:46

+0

什麼是RelationParse和TestParse？ – user4333097 2014-12-07 23:10:27

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