java - 如何让这个简单的笔记应用程序正常工作？

Question

我是android编程新手，我似乎找不到以下程序的问题:

主类:

public class MainActivity extends Activity {

    ListView listView;
    ArrayList<String> listItems = new ArrayList<String>();
    ArrayAdapter<String> adapter;

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

        listView = (ListView) findViewById(R.id.listView1);
        adapter = new ArrayAdapter<String>(this, R.layout.my_list_layout,
                listItems);
        listView.setAdapter(adapter);
    }

    @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;
    }

    public boolean onOptionsItemSelected(MenuItem item) {

        switch (item.getItemId()) {

        case R.id.menu_insert:

            createReminder();
            return true;

        }
        return super.onOptionsItemSelected(item);
    }

    private static final int ACTIVITY_CREATE = 0;

    private void createReminder() {

        Intent intent = new Intent(this, ReminderEditActivity.class);
        startActivityForResult(intent, ACTIVITY_CREATE);
    }

    protected void onActivityResult(int requestCode, int resultCode,
            Intent intent) {

        if (resultCode == RESULT_OK) {

            listItems.add(intent.getStringExtra("reminder_text"));
            adapter.notifyDataSetChanged();
        }

    }

}

中学类:

public class ReminderEditActivity extends Activity {

    EditText editText;

    public void onCreate(Bundle b) {

        super.onCreate(b);
        setContentView(R.layout.reminder_edit);

        editText = (EditText) findViewById(R.id.editText1);
    }

    public void onPostButtonClick(View view) {

        Intent intent = new Intent();
        intent.putExtra("text", editText.getText().toString());
        setResult(Activity.RESULT_OK, intent);
        finish();
    }
}

所以程序启动正常，当我单击添加按钮时，我被带到第二页带有预期的文本字段和按钮。当我填写字段并单击按钮时，程序崩溃了。我遇到了空指针异常，但它没有指向我的代码中的任何位置，只是指向数组适配器代码(更具体地说是 ArrayAdapter.java:394)。我有一些编程经验，但我是调试 android 项目的新手。任何方向将不胜感激。

堆栈跟踪:

12-23 18:08:37.881: D/dalvikvm(1654): GC_FOR_ALLOC freed 71K, 5% free 2989K/3136K, paused 40ms, total 43ms
12-23 18:08:37.891: I/dalvikvm-heap(1654): Grow heap (frag case) to 3.596MB for 635812-byte allocation
12-23 18:08:37.951: D/dalvikvm(1654): GC_FOR_ALLOC freed 3K, 5% free 3606K/3760K, paused 56ms, total 56ms
12-23 18:08:38.251: D/gralloc_goldfish(1654): Emulator without GPU emulation detected.
12-23 18:09:07.971: I/Choreographer(1654): Skipped 82 frames!  The application may be doing too much work on its main thread.
12-23 18:09:08.151: I/Choreographer(1654): Skipped 39 frames!  The application may be doing too much work on its main thread.
12-23 18:09:10.231: I/Choreographer(1654): Skipped 33 frames!  The application may be doing too much work on its main thread.
12-23 18:09:17.151: D/AndroidRuntime(1654): Shutting down VM
12-23 18:09:17.151: W/dalvikvm(1654): threadid=1: thread exiting with uncaught exception (group=0xb3a19b90)
12-23 18:09:17.261: E/AndroidRuntime(1654): FATAL EXCEPTION: main
12-23 18:09:17.261: E/AndroidRuntime(1654): Process: food.start.thefoodapp, PID: 1654
12-23 18:09:17.261: E/AndroidRuntime(1654): java.lang.NullPointerException
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:394)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.widget.ArrayAdapter.getView(ArrayAdapter.java:362)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.widget.AbsListView.obtainView(AbsListView.java:2263)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.widget.ListView.measureHeightOfChildren(ListView.java:1263)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.widget.ListView.onMeasure(ListView.java:1175)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.view.View.measure(View.java:16458)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.widget.RelativeLayout.measureChild(RelativeLayout.java:689)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:473)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.view.View.measure(View.java:16458)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.view.View.measure(View.java:16458)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at com.android.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:327)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.view.View.measure(View.java:16458)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2289)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.view.View.measure(View.java:16458)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1914)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1111)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1293)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:998)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5582)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.view.Choreographer.doCallbacks(Choreographer.java:562)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.view.Choreographer.doFrame(Choreographer.java:532)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.os.Handler.handleCallback(Handler.java:733)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.os.Handler.dispatchMessage(Handler.java:95)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.os.Looper.loop(Looper.java:137)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at android.app.ActivityThread.main(ActivityThread.java:4998)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at java.lang.reflect.Method.invokeNative(Native Method)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at java.lang.reflect.Method.invoke(Method.java:515)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
12-23 18:09:17.261: E/AndroidRuntime(1654):     at dalvik.system.NativeStart.main(Native Method)
12-23 18:09:21.121: I/Process(1654): Sending signal. PID: 1654 SIG: 9

这是 my_list_layout.xml:

<?xml version="1.0" encoding="UTF-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/identView"
android:layout_width="wrap_content"
android:layout_height="wrap_content">

</TextView>

Answer 1

请参阅此答案 ( android - ArrayAdapter.createViewFromResource(int, View, ViewGroup, int) line: 355 NullPointerException )。

这可能与您的 my_list_layout 以及适配器如何尝试将给定的字符串值填充到其中有关。特别是，ArrayAdapter 文档指出:

By default this class expects that the provided resource id references a single TextView

如果这不是所需的行为，请修改您的布局或创建 ArrayAdapter 的子类并重写 getView() 方法。

ArrayAdapter 文档:http://developer.android.com/reference/android/widget/ArrayAdapter.html

编辑:关于布局或扩展 ArrayAdapter 的更多详细信息，布局应如下所示，其中 TextView 位于布局的根部。

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />

另一方面，如果你想扩展ArrayAdapter(这很常见)，你可以在Google上查看一些教程，或者看看本教程中的3.2节:

http://www.vogella.com/articles/AndroidListView/article.html

祝一切顺利!