2

我是 Android 应用程序开发的新手，有一个小问题。

我试图按照一个示例来创建一个待办事项列表应用程序。但是，即使我完全复制了它，它也不起作用。

当我运行它时它没有显示任何错误，但是会出现一个空白屏幕，几秒钟后它会关闭并显示“不幸的是，ToDoList 已停止”。

有谁知道这个问题可能是什么？

代码

 package com.paad.todolist;

    import java.util.ArrayList;

    import android.app.Activity;
    import android.os.Bundle;
    import android.view.KeyEvent;
    import android.view.Menu;
    import android.view.View;
    import android.widget.ArrayAdapter;
    import android.widget.EditText;
    import android.widget.ListView;

    public class MainActivity extends Activity {

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);

            setContentView(R.layout.activity_main);

            ListView myListView = (ListView)findViewById(R.id.ListView);
            final EditText myEditText = (EditText) findViewById(R.id.EditText);

            final ArrayList<String> todoItems = new ArrayList<String>();
            final ArrayAdapter<String> aa;

            aa = new ArrayAdapter<String> (this,android.R.layout.simple_list_item_1,todoItems);

            myListView.setAdapter(aa);


        myEditText.setOnKeyListener(new View.OnKeyListener()   {
            public boolean onKey(View v, int keyCode, KeyEvent event)   {
                if (event.getAction() == KeyEvent.ACTION_DOWN)
                    if ((keyCode == KeyEvent.KEYCODE_DPAD_CENTER)    ||
                        (keyCode == KeyEvent.KEYCODE_ENTER))   {
                        todoItems.add(0, myEditText.getText().toString());
                        aa.notifyDataSetChanged();
                        myEditText.setText("");
                        return true;
                    }
                return false;
            }
        });
    }

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

    }

布局 XML 文件

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

    <EditText 
        android:id="@+id/EditText"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="@string/addItemHint"
        android:contentDescription="@string/addItemContentDescription"
    />

    <ListView
        android:id="@+id/ListView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
    />        

</LinearLayout>

日志：

02-10 20:03:53.850: D/AndroidRuntime(24220): Shutting down VM
02-10 20:03:53.850: W/dalvikvm(24220): threadid=1: thread exiting with uncaught exception (group=0x40f0a2a0)
02-10 20:03:53.850: E/AndroidRuntime(24220): FATAL EXCEPTION: main
02-10 20:03:53.850: E/AndroidRuntime(24220): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.paad.todolist/com.paad.todolist.MainActivity}: java.lang.NullPointerException
02-10 20:03:53.850: E/AndroidRuntime(24220):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2100)
02-10 20:03:53.850: E/AndroidRuntime(24220):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2125)
02-10 20:03:53.850: E/AndroidRuntime(24220):    at android.app.ActivityThread.access$600(ActivityThread.java:140)
02-10 20:03:53.850: E/AndroidRuntime(24220):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1227)
02-10 20:03:53.850: E/AndroidRuntime(24220):    at android.os.Handler.dispatchMessage(Handler.java:99)
02-10 20:03:53.850: E/AndroidRuntime(24220):    at android.os.Looper.loop(Looper.java:137)
02-10 20:03:53.850: E/AndroidRuntime(24220):    at android.app.ActivityThread.main(ActivityThread.java:4898)
02-10 20:03:53.850: E/AndroidRuntime(24220):    at java.lang.reflect.Method.invokeNative(Native Method)
02-10 20:03:53.850: E/AndroidRuntime(24220):    at java.lang.reflect.Method.invoke(Method.java:511)
02-10 20:03:53.850: E/AndroidRuntime(24220):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1006)
02-10 20:03:53.850: E/AndroidRuntime(24220):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:773)
02-10 20:03:53.850: E/AndroidRuntime(24220):    at dalvik.system.NativeStart.main(Native Method)
02-10 20:03:53.850: E/AndroidRuntime(24220): Caused by: java.lang.NullPointerException
02-10 20:03:53.850: E/AndroidRuntime(24220):    at com.paad.todolist.MainActivity.onCreate(MainActivity.java:30)
02-10 20:03:53.850: E/AndroidRuntime(24220):    at android.app.Activity.performCreate(Activity.java:5206)
02-10 20:03:53.850: E/AndroidRuntime(24220):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1083)
02-10 20:03:53.850: E/AndroidRuntime(24220):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2064)
02-10 20:03:53.850: E/AndroidRuntime(24220):    ... 11 more
4

2 回答 2

0

您的代码运行良好。如前所述，您可能没有在清单中定义您的活动。为此，请在项目根目录中的清单文件中执行以下操作。

<activity
        android:label="@string/app_name"
        android:name=".Activityname" >
</activity>
于 2013-04-13T22:31:22.783 回答
0

它不起作用，因为您没有在 android 清单 XML 中正确定义您的活动。

于 2013-04-13T17:46:31.450 回答