內容解析器查詢NullException

我正在試圖用存儲在外部存儲捲上的音樂填充ListView。內容解析器查詢NullException

我已經分離出一個較大的項目的代碼，但錯誤是一樣的。在我隔離的測試程序中，我有一個按下的按鈕，應該填充一個ListView。我標出了引發錯誤的那一行。

package com.example.crtest; 

import android.net.Uri; 
import android.os.Bundle; 
import android.provider.MediaStore; 
import android.app.Activity; 
import android.content.ContentResolver; 
import android.database.Cursor; 
import android.support.v4.widget.SimpleCursorAdapter; 
import android.util.Log; 
import android.view.Menu; 
import android.view.View; 
import android.widget.ListView; 

public class MainActivity extends Activity { 

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

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.main, menu); 
     return true; 
    } 

    ListView mList; 
    Cursor cu; 
    ContentResolver cr; 

    public void fillMeUp(View view) { 
     Log.i("FillMeUp", "FMU start."); 
     String[] proj = { 
       MediaStore.Audio.Media._ID, 
       MediaStore.Audio.Media.ARTIST, 
       MediaStore.Audio.Media.ALBUM }; 
     Uri uri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI; 
     Log.i("FillMeUp", uri.toString()); 

     // This is where I get an FATAL EXCEPTION 
     cu = cr.query(uri, proj, MediaStore.Audio.Media.IS_MUSIC + "=1", null, null); 
     Log.i("FillMeUp", "Query finished. " + (cu == null ? "Returned NULL." : "Returned a cursor.")); 

     Log.i("FillMeUp", "FMU with some text."); 

     mList = (ListView) findViewById(R.id.lv); 
     @SuppressWarnings("deprecation") 
     SimpleCursorAdapter adapter = new SimpleCursorAdapter(
       this, 
       android.R.layout.simple_list_item_1, 
       cu, 
       new String[] { "bla" }, 
       new int[] { android.R.id.text1, android.R.id.text2 } 
       ); 
     mList.setAdapter(adapter); 
     Log.i("FillMeUp", "FMU mlist done."); 
    } 
}

這就是LogCat吐出來的東西。

07-19 23:07:09.613: E/Trace(30502): error opening trace file: No such file or directory (2) 
07-19 23:07:09.763: D/libEGL(30502): loaded /system/lib/egl/libEGL_mali.so 
07-19 23:07:09.763: D/libEGL(30502): loaded /system/lib/egl/libGLESv1_CM_mali.so 
07-19 23:07:09.768: D/libEGL(30502): loaded /system/lib/egl/libGLESv2_mali.so 
07-19 23:07:09.768: E/(30502): Device driver API match 
07-19 23:07:09.768: E/(30502): Device driver API version: 17 
07-19 23:07:09.768: E/(30502): User space API version: 17 
07-19 23:07:09.773: E/(30502): mali: REVISION=Linux-r3p1-01rel1 BUILD_DATE=Mon May 13 15:55:05 KST 2013 
07-19 23:07:09.803: D/OpenGLRenderer(30502): Enabling debug mode 0 
07-19 23:07:12.408: I/FillMeUp(30502): FMU start. 
07-19 23:07:12.408: I/FillMeUp(30502): content://media/external/audio/media 
07-19 23:07:12.408: D/AndroidRuntime(30502): Shutting down VM 
07-19 23:07:12.408: W/dalvikvm(30502): threadid=1: thread exiting with uncaught exception (group=0x40bcc930) 
07-19 23:07:12.423: E/AndroidRuntime(30502): FATAL EXCEPTION: main 
07-19 23:07:12.423: E/AndroidRuntime(30502): java.lang.IllegalStateException: Could not execute method of the activity 
07-19 23:07:12.423: E/AndroidRuntime(30502):  at android.view.View$1.onClick(View.java:3606) 
07-19 23:07:12.423: E/AndroidRuntime(30502):  at android.view.View.performClick(View.java:4211) 
07-19 23:07:12.423: E/AndroidRuntime(30502):  at android.view.View$PerformClick.run(View.java:17362) 
07-19 23:07:12.423: E/AndroidRuntime(30502):  at android.os.Handler.handleCallback(Handler.java:725) 
07-19 23:07:12.423: E/AndroidRuntime(30502):  at android.os.Handler.dispatchMessage(Handler.java:92) 
07-19 23:07:12.423: E/AndroidRuntime(30502):  at android.os.Looper.loop(Looper.java:137) 
07-19 23:07:12.423: E/AndroidRuntime(30502):  at android.app.ActivityThread.main(ActivityThread.java:5227) 
07-19 23:07:12.423: E/AndroidRuntime(30502):  at java.lang.reflect.Method.invokeNative(Native Method) 
07-19 23:07:12.423: E/AndroidRuntime(30502):  at java.lang.reflect.Method.invoke(Method.java:511) 
07-19 23:07:12.423: E/AndroidRuntime(30502):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795) 
07-19 23:07:12.423: E/AndroidRuntime(30502):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:562) 
07-19 23:07:12.423: E/AndroidRuntime(30502):  at dalvik.system.NativeStart.main(Native Method) 
07-19 23:07:12.423: E/AndroidRuntime(30502): Caused by: java.lang.reflect.InvocationTargetException 
07-19 23:07:12.423: E/AndroidRuntime(30502):  at java.lang.reflect.Method.invokeNative(Native Method) 
07-19 23:07:12.423: E/AndroidRuntime(30502):  at java.lang.reflect.Method.invoke(Method.java:511) 
07-19 23:07:12.423: E/AndroidRuntime(30502):  at android.view.View$1.onClick(View.java:3601) 
07-19 23:07:12.423: E/AndroidRuntime(30502):  ... 11 more 
07-19 23:07:12.423: E/AndroidRuntime(30502): Caused by: java.lang.NullPointerException 
07-19 23:07:12.423: E/AndroidRuntime(30502):  at com.example.crtest.MainActivity.fillMeUp(MainActivity.java:44) 
07-19 23:07:12.423: E/AndroidRuntime(30502):  ... 14 more

我對Android比較陌生，但我之前和Java一起工作過。我的編程技巧雖然生疏，但通常都可以。但我在這裏虧本。使用Google和Stack，現在正在處理這個問題兩天了。溢出讓我無處可尋。

來源

2013-07-19 dav0rs

你在哪裏調用'fillMeUp'方法和其中ContentResolver的初始化？ – Desert

您的內容分解爲空，如果你還想要得到保存在外部存儲使用context.managedQuery的所有音樂。看看這個：Android external storage或Get filename and path from URI from mediastore。

來源

2013-07-19 23:07:13 Tobiel

添加

cr = getContentResolver();

這將返回ContentResolver的corresping到當前上下文。

來源

2014-06-06 13:39:44

內容解析器查詢NullException

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