Question

当我运行此代码时：

    package com.herring.android.finalproject;


    import android.app.ListActivity;
    import android.content.Intent;
    import android.database.Cursor;
    import android.os.Bundle;
    import android.view.View;
    import android.widget.ListView;
    import android.widget.SimpleCursorAdapter;
    public class GamesListActivity extends ListActivity {
        private Cursor gamesCursor;
        private GameDataBaseManager mDbHelper;
        public void onCreate(Bundle savedInstanceState)
        {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.toprated);
            mDbHelper = new GameDataBaseManager(this);
            mDbHelper.open();
            fillData();
            registerForContextMenu(getListView());
            final ListView lv = (ListView) findViewById(R.id.text1);
            lv.setOnClickListener(new View.OnClickListener(){
                public void onClick(View v)
                {
                    Intent i = new Intent(GamesListActivity.this, Game.class);
                    startActivityForResult(i, 0);
                }
            });

        }
        private void fillData()
        {
            gamesCursor = mDbHelper.getAllGames();
            startManagingCursor(gamesCursor);
            String[] from = new String[]{GameDataBaseManager.KEY_TITLE};
            int[] to = new int[]{R.id.text1};
            SimpleCursorAdapter games = new SimpleCursorAdapter(this, R.layout.toprateditem, gamesCursor, from, to);
            setListAdapter(games);
        }
    }

我在Logcat中得到了这个：

01-18 17:46:08.742: ERROR/AndroidRuntime(1382): Uncaught handler: thread main exiting due to uncaught exception
01-18 17:46:08.752: ERROR/AndroidRuntime(1382): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.herring.android.finalproject/com.herring.android.finalproject.GamesListActivity}: java.lang.NullPointerException
01-18 17:46:08.752: ERROR/AndroidRuntime(1382):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2496)
01-18 17:46:08.752: ERROR/AndroidRuntime(1382):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512)
01-18 17:46:08.752: ERROR/AndroidRuntime(1382):     at android.app.ActivityThread.access$2200(ActivityThread.java:119)
01-18 17:46:08.752: ERROR/AndroidRuntime(1382):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863)
01-18 17:46:08.752: ERROR/AndroidRuntime(1382):     at android.os.Handler.dispatchMessage(Handler.java:99)
01-18 17:46:08.752: ERROR/AndroidRuntime(1382):     at android.os.Looper.loop(Looper.java:123)
01-18 17:46:08.752: ERROR/AndroidRuntime(1382):     at android.app.ActivityThread.main(ActivityThread.java:4363)
01-18 17:46:08.752: ERROR/AndroidRuntime(1382):     at java.lang.reflect.Method.invokeNative(Native Method)
01-18 17:46:08.752: ERROR/AndroidRuntime(1382):     at java.lang.reflect.Method.invoke(Method.java:521)
01-18 17:46:08.752: ERROR/AndroidRuntime(1382):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
01-18 17:46:08.752: ERROR/AndroidRuntime(1382):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
01-18 17:46:08.752: ERROR/AndroidRuntime(1382):     at dalvik.system.NativeStart.main(Native Method)
01-18 17:46:08.752: ERROR/AndroidRuntime(1382): Caused by: java.lang.NullPointerException
01-18 17:46:08.752: ERROR/AndroidRuntime(1382):     at com.herring.android.finalproject.GamesListActivity.onCreate(GamesListActivity.java:23)
01-18 17:46:08.752: ERROR/AndroidRuntime(1382):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
01-18 17:46:08.752: ERROR/AndroidRuntime(1382):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2459)
01-18 17:46:08.752: ERROR/AndroidRuntime(1382):     ... 11 more

错误发生在lv.setOnClickListener 我到处寻找答案，但他们似乎都在谈论缺少setContentView，我不是。我完全迷失了。任何帮助将不胜感激。

编辑：这是我的toprated.xml

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

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


</LinearLayout>

Answer 1

final ListView lv = (ListView) findViewById(R.id.text1);

而不是为什么不只是做getListView（）？像下面这样的东西试试？

final ListView lv = getListView();

Answer 2

使用ListActivity时，您必须设置ListView ID，如下所示：android:id="@+id/android:list"

Answer 3

您将listView id设置为text1，但未在布局中声明它。您实现listactivity类，以便您可以通过这种方式调用listview

final ListView lv = getListView();

您已在Layout中声明了listview magic id，因此不需要使用findViewById（）方法。您可以使用final ListView lv = getListView();

代替此操作

所以写下面的代码：

final ListView lv = getListView();
            lv.setOnClickListener(new View.OnClickListener(){
                public void onClick(View v)
                {
                    Intent i = new Intent(GamesListActivity.this, Game.class);
                    startActivityForResult(i, 0);
                }
            });

无法启动由NullPointerException引起的活动ComponentInfo

3 个答案: