我的代碼有什麼問題？ （顯示java.lang.NullPointerException）

Question

我有這樣的功能：

public static String getXML(int id, int choose, int foo){  
     String line = null; 
     try { 
      StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build(); 
      StrictMode.setThreadPolicy(policy); 
      DefaultHttpClient httpClient = new DefaultHttpClient(); 
      HttpPost httpPost = null; 
      if(id == 100) 
      { 
       httpPost = new HttpPost("http://andronekat.com/sawalef/logFollow.php?id="+ foo + ""); 
      } 
      else if(id == 20) 
      { 
       httpPost = new HttpPost("http://andronekat.com/sawalef/logMyTimeLine.php?id="+ foo + ""); 
      } 
      else if(id == 19) 
      { 
       httpPost = new HttpPost("http://andronekat.com/sawalef/logMyEntity.php?id="+ foo + ""); 
      } 
      else if(choose == 1) 
      { 
       httpPost = new HttpPost("http://andronekat.com/sawalef/log.php?id="+ id + ""); 
      } 
      else if(choose == 2) 
       httpPost = new HttpPost("http://andronekat.com/sawalef/log2.php?id="+ id + ""); 
      else if(choose == 3) 
       httpPost = new HttpPost("http://andronekat.com/sawalef/comments.php?tag="+ id + ""); 
      HttpResponse httpResponse = httpClient.execute(httpPost); 
      HttpEntity httpEntity = httpResponse.getEntity(); 
      line = EntityUtils.toString(httpEntity, "UTF-8"); 

     } 

所有字符串URL工作正常，除了第一ULR是：

if(id == 100) 
    { 
     httpPost = new HttpPost("http://andronekat.com/sawalef/logFollow.php?id="+ foo + ""); 
    } 

它給我顯示java.lang.NullPointerException在這一行

HttpResponse httpResponse = httpClient.execute(httpPost); 

我不知道從哪裏得到空。如果我把它放在瀏覽器中，鏈接工作正常。任何人都可以幫助我嗎？

的logcat：

04-28 09:37:34.500: E/AndroidRuntime(21842): FATAL EXCEPTION: main 
04-28 09:37:34.500: E/AndroidRuntime(21842): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.softshell.sowalef/com.softshell.sowalef.Follow}: java.lang.NullPointerException 
04-28 09:37:34.500: E/AndroidRuntime(21842): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2100) 
04-28 09:37:34.500: E/AndroidRuntime(21842): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2125) 
04-28 09:37:34.500: E/AndroidRuntime(21842): at android.app.ActivityThread.access$600(ActivityThread.java:140) 
04-28 09:37:34.500: E/AndroidRuntime(21842): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1227) 
04-28 09:37:34.500: E/AndroidRuntime(21842): at android.os.Handler.dispatchMessage(Handler.java:99) 
04-28 09:37:34.500: E/AndroidRuntime(21842): at android.os.Looper.loop(Looper.java:137) 
04-28 09:37:34.500: E/AndroidRuntime(21842): at android.app.ActivityThread.main(ActivityThread.java:4898) 
04-28 09:37:34.500: E/AndroidRuntime(21842): at java.lang.reflect.Method.invokeNative(Native Method) 
04-28 09:37:34.500: E/AndroidRuntime(21842): at java.lang.reflect.Method.invoke(Method.java:511) 
04-28 09:37:34.500: E/AndroidRuntime(21842): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1008) 
04-28 09:37:34.500: E/AndroidRuntime(21842): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:775) 
04-28 09:37:34.500: E/AndroidRuntime(21842): at dalvik.system.NativeStart.main(Native Method) 
04-28 09:37:34.500: E/AndroidRuntime(21842): Caused by: java.lang.NullPointerException 
04-28 09:37:34.500: E/AndroidRuntime(21842): at com.softshell.sowalef.Follow.onCreate(Follow.java:71) 
04-28 09:37:34.500: E/AndroidRuntime(21842): at android.app.Activity.performCreate(Activity.java:5206) 
04-28 09:37:34.500: E/AndroidRuntime(21842): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094) 
04-28 09:37:34.500: E/AndroidRuntime(21842): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2064) 
04-28 09:37:34.500: E/AndroidRuntime(21842): ... 11 more 

Answer 1

你一定是id在失敗的情況下設置爲100？

即使你是，你的代碼中有一個應該修復的漏洞。具體而言，id既不是100,20也不是19和choose既不是1,2也不是3。

而且，如果（我保證，它應該仍然是固定的），你也應該在execute調用之前檢查您的httpPost和httpClient值，這不是你的具體問題就在這裏，所以你可以更容易地找出問題出在哪裏所在。