Question

我尝试将字符串从活动发送到选项卡中的片段，但我不断获得空堆栈指针异常。这是主活动中将字符串发送到片段

的代码部分

//this portion of code  sends the user_name to the note fragment
Bundle bundle = new Bundle();
bundle.putString("name", name);
NoteFragment NF = new NoteFragment();
NF.setArguments(bundle);

这段代码接收片段类中的字符串。

//fragment class
public class NoteFragment extends Fragment{
    View v;
    String note, name, timestamp;
    EditText NOTE;
    noteOperations NO;
    Context ctx;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
        v = inflater.inflate(R.layout.notelayout, container, false);
        ctx = getActivity().getApplicationContext();
        NOTE = (EditText) v.findViewById(R.id.note);
        NO = new noteOperations(ctx);
        name = getArguments().getString("name");
        ImageButton save = (ImageButton) v.findViewById(R.id.saveButton);
        save.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View arg0) {
                note = NOTE.getText().toString();
                if (!note.equals(""))
                {
                    timestamp = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(Calendar.getInstance     ().getTime());
                    NO.putInformation(NO,   note, timestamp, name);
                    NOTE.setText("");
                }
            }
        });
        return v;
    }
}

这是logcat

10-04 06:52:48.848: D/Databsse operations(876): Database created
    10-04 06:52:50.151: D/Databsse operations(876): One row inserted
    10-04 06:52:51.207: D/gralloc_goldfish(876): Emulator without GPU emulation detected.
    10-04 06:53:35.698: I/Choreographer(876): Skipped 49 frames!  The application may be doing too much work on its main thread.
    10-04 06:53:36.648: D/dalvikvm(876): GC_CONCURRENT freed 72K, 7% free 2716K/2908K, paused 15ms+175ms, total 1283ms
    10-04 06:53:38.288: I/Choreographer(876): Skipped 130 frames!  The application may be doing too much work on its main thread.
    10-04 06:53:44.859: I/Choreographer(876): Skipped 34 frames!  The application may be doing too much work on its main thread.
    10-04 06:53:49.748: D/Databsse operations(876): Database created
    10-04 06:53:49.918: D/Databsse operations(876): Table combed
    10-04 06:53:50.291: I/Choreographer(876): Skipped 147 frames!  The application may be doing too much work on its main thread.
    10-04 06:53:50.648: I/Choreographer(876): Skipped 41 frames!  The application may be doing too much work on its main thread.
    10-04 06:53:53.247: D/dalvikvm(876): GC_FOR_ALLOC freed 208K, 11% free 2892K/3224K, paused 501ms, total 555ms
    10-04 06:53:53.378: I/dalvikvm-heap(876): Grow heap (frag case) to 3.545MB for 635812-byte allocation
    10-04 06:53:53.858: D/dalvikvm(876): GC_FOR_ALLOC freed 2K, 9% free 3511K/3848K, paused 481ms, total 482ms
    10-04 06:53:54.938: D/AndroidRuntime(876): Shutting down VM
    10-04 06:53:54.958: W/dalvikvm(876): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
    10-04 06:53:55.128: D/dalvikvm(876): GC_CONCURRENT freed 33K, 9% free 3518K/3848K, paused 89ms+281ms, total 1265ms
    10-04 06:53:55.258: E/AndroidRuntime(876): FATAL EXCEPTION: main
    10-04 06:53:55.258: E/AndroidRuntime(876): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.databank/com.example.databank.Dashboard}: java.lang.NullPointerException
    10-04 06:53:55.258: E/AndroidRuntime(876):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
    10-04 06:53:55.258: E/AndroidRuntime(876):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
    10-04 06:53:55.258: E/AndroidRuntime(876):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
    10-04 06:53:55.258: E/AndroidRuntime(876):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
    10-04 06:53:55.258: E/AndroidRuntime(876):  at android.os.Handler.dispatchMessage(Handler.java:99)
    10-04 06:53:55.258: E/AndroidRuntime(876):  at android.os.Looper.loop(Looper.java:137)
    10-04 06:53:55.258: E/AndroidRuntime(876):  at android.app.ActivityThread.main(ActivityThread.java:5041)
    10-04 06:53:55.258: E/AndroidRuntime(876):  at java.lang.reflect.Method.invokeNative(Native Method)
    10-04 06:53:55.258: E/AndroidRuntime(876):  at java.lang.reflect.Method.invoke(Method.java:511)
    10-04 06:53:55.258: E/AndroidRuntime(876):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
    10-04 06:53:55.258: E/AndroidRuntime(876):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
    10-04 06:53:55.258: E/AndroidRuntime(876):  at dalvik.system.NativeStart.main(Native Method)
    10-04 06:53:55.258: E/AndroidRuntime(876): Caused by: java.lang.NullPointerException
    10-04 06:53:55.258: E/AndroidRuntime(876):  at com.example.databank.NoteFragment.<init>(NoteFragment.java:17)
    10-04 06:53:55.258: E/AndroidRuntime(876):  at com.example.databank.Dashboard.onCreate(Dashboard.java:38)
    10-04 06:53:55.258: E/AndroidRuntime(876):  at android.app.Activity.performCreate(Activity.java:5104)
    10-04 06:53:55.258: E/AndroidRuntime(876):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
    10-04 06:53:55.258: E/AndroidRuntime(876):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
    10-04 06:53:55.258: E/AndroidRuntime(876):  ... 11 more
    10-04 06:54:01.578: I/Process(876): Sending signal. PID: 876 SIG: 9
    10-04 06:54:04.928: D/Databsse operations(900): Database created
    10-04 06:54:06.328: D/Databsse operations(900): One row inserted
    10-04 06:54:07.408: I/Choreographer(900): Skipped 52 frames!  The application may be doing too much work on its main thread.
    10-04 06:54:07.498: D/gralloc_goldfish(900): Emulator without GPU emulation detected.

Answer 1

堆栈跟踪清楚地表明您的NullPointerException位于NoteFragment.java中的第17行

您不包含行号，但您示例的第16行和第17行是：

ImageButton save = (ImageButton) v.findViewById(R.id.saveButton);
save.setOnClickListener(new View.OnClickListener() {

所以我猜测你的变量“保存”＃39;为空，因为v.findViewById(R.id.saveButton)没有找到任何内容。

哦，它是一个NullPointerException，而不是＆＃34; null stackpointer exception＆＃34;这与堆栈无关。

Answer 2

在fragment类中，我初始化了一个新的bundle。这是修改

Bundle bundle = new Bundle();
String name = bundle.getString("name");

这纠正了空指针异常

Answer 3

如果初始化Bundle并且它纠正了空指针异常，那意味着getArguments（）返回null。这也意味着你没有解决问题。现在String名称为null。

确保在添加片段时，您正在添加名为setArguments（）的实例，而不是创建新实例。

像这样修改你的代码来处理异常：

Bundle b;
if ((b = getArguments()) != null) {
    name = b.getString("name");
} else {
    name = "";
    Log.v(TAG, "No arguments set for NoteFragment")
}

空堆栈指针异常

3 个答案: