访问收件箱的信息报错

我想访问收件箱信息，写了如下代码：

Uri uriSMSURI = Uri.parse("content://sms/inbox");
    Cursor cur = getContentResolver().query(uriSMSURI, null, null, null,null);
    String sms = "";
    cur.moveToNext();
    sms = cur.getString(0);

然后报出如下错误：

01-07 12:31:37.222: E/AndroidRuntime(687): FATAL EXCEPTION: main
01-07 12:31:37.222: E/AndroidRuntime(687): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.inboxshowingapp/com.example.inboxshowingapp.MainActivity}: android.database.CursorIndexOutOfBoundsException: Index 0 requested, with a size of 0
01-07 12:31:37.222: E/AndroidRuntime(687):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
01-07 12:31:37.222: E/AndroidRuntime(687):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
01-07 12:31:37.222: E/AndroidRuntime(687):  at android.app.ActivityThread.access$2300(ActivityThread.java:125)
01-07 12:31:37.222: E/AndroidRuntime(687):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
01-07 12:31:37.222: E/AndroidRuntime(687):  at android.os.Handler.dispatchMessage(Handler.java:99)
01-07 12:31:37.222: E/AndroidRuntime(687):  at android.os.Looper.loop(Looper.java:123)
01-07 12:31:37.222: E/AndroidRuntime(687):  at android.app.ActivityThread.main(ActivityThread.java:4627)
01-07 12:31:37.222: E/AndroidRuntime(687):  at java.lang.reflect.Method.invokeNative(Native Method)
01-07 12:31:37.222: E/AndroidRuntime(687):  at java.lang.reflect.Method.invoke(Method.java:521)
01-07 12:31:37.222: E/AndroidRuntime(687):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
01-07 12:31:37.222: E/AndroidRuntime(687):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
01-07 12:31:37.222: E/AndroidRuntime(687):  at dalvik.system.NativeStart.main(Native Method)
01-07 12:31:37.222: E/AndroidRuntime(687): Caused by: android.database.CursorIndexOutOfBoundsException: Index 0 requested, with a size of 0
01-07 12:31:37.222: E/AndroidRuntime(687):  at android.database.AbstractCursor.checkPosition(AbstractCursor.java:580)
01-07 12:31:37.222: E/AndroidRuntime(687):  at android.database.AbstractWindowedCursor.checkPosition(AbstractWindowedCursor.java:214)
01-07 12:31:37.222: E/AndroidRuntime(687):  at android.database.AbstractWindowedCursor.getString(AbstractWindowedCursor.java:41)
01-07 12:31:37.222: E/AndroidRuntime(687):  at android.database.CursorWrapper.getString(CursorWrapper.java:135)
01-07 12:31:37.222: E/AndroidRuntime(687):  at com.example.inboxshowingapp.MainActivity.onCreate(MainActivity.java:32)
01-07 12:31:37.222: E/AndroidRuntime(687):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
01-07 12:31:37.222: E/AndroidRuntime(687):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
01-07 12:31:37.222: E/AndroidRuntime(687):  ... 11 more