当我使用内容解析器发送查询时，Cursor为null

Question

private static final int USER_ID=1;
private static final int DT=2;
private static final int VALUES_ALL=3;
 private static final UriMatcher sUriMacher= new UriMatcher(UriMatcher.NO_MATCH);
    static{




sUriMacher.addURI("gr.hua.android.contentproviderapp","COORDINATES",VALUES_ALL);
sUriMacher.addURI("gr.hua.android.contentproviderapp","COORDINATES/#",USER_ID);
sUriMacher.addURI("gr.hua.android.contentproviderapp","COORDINATES/#",DT);

     }
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
        SQLiteDatabase db = new DBHelper(getContext()).getReadableDatabase();
        switch (sUriMacher.match(uri)){
            case USER_ID:
                String[] selargs =new String[1];  
                selargs[0]=uri.getLastPathSegment();  //the user_Id that i got
                String user=DBHelper.USER_ID;

            String[] coll =new String[1]; //the collums that i want to select
            coll[0]=DBHelper.KEY_LATITUDE;
            coll[1]=DBHelper.KEY_LONGITUDE; 

            return db.query(DBHelper.TABLE_NAME,coll,user+"=?",selargs,null,null,null);
        case DT:
            String[] selargs2 =new String[1];
            selargs2[0]=uri.getLastPathSegment();
            String[] coll2 =new String[1];
            coll2[0]=DBHelper.KEY_LATITUDE;
            coll2[1]=DBHelper.KEY_LONGITUDE;
            return db.query(DBHelper.TABLE_NAME,coll2,"_DT=?",selargs2,null,null,null); //the same as the user_id but we get the dt here
        case VALUES_ALL:
            return db.query(DBHelper.TABLE_NAME,null,null,null,null,null,null);
        default:
    }
    return null;
}

有我的内容提供商，我在这里执行插入方法

Uri result =Uri.withAppendedPath(url,get3);

Cursor cursor =resolver.query(result,null,null,null,null);

 if (cursor!=null && cursor.getCount()>0){  //i got null here 
                    StringBuilder stringBuilder =new StringBuilder("");
                    while (cursor.moveToNext()) 
                     stringBuilder.append(cursor.getString(0) + " " + cursor.getString(1) + "");
                    }

                    get.setText(stringBuilder.toString());
                }else{
                    get.setText("This user not found");

上面的代码是我想从edittext（get3）获取的内容解析器，它是一个String类型的user_id，并将其作为LastPathSegment放在url路径中但是游标重新返回null总是 如果我发送做选择的网址所有的工作 我在网上搜索我做了一些改变，但是当我调试时，我没有得到Cursor = null