创建导航面板时崩溃

Question

我正在尝试在Android中制作一个导航面板。 我遵循了http://developer.android.com/training/implementing-navigation/nav-drawer.html中的说明。 但是，应用程序由于空指针异常而崩溃。

MainActivity.java

//import statements

public class MainActivity extends ActionBarActivity {
    private String[] mPlanetTitles;
    private DrawerLayout mDrawerLayout;
    private ListView mDrawerList;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mPlanetTitles = getResources().getStringArray(R.array.nav_drawer_items);
        mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
        mDrawerList = (ListView) findViewById(R.id.left_drawer);

        // Set the adapter for the list view
        mDrawerList.setAdapter(new ArrayAdapter<String>(this,R.layout.activity_main,
                R.layout.drawer_listview_item, mPlanetTitles));
        // Set the list's click listener
//        mDrawerList.setOnItemClickListener(new DrawerItemClickListener());
    }


    @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;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

activity_main.xml中

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
   >

    <android.support.v4.widget.DrawerLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/drawer_layout"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <!-- The main content view -->
        <FrameLayout
            android:id="@+id/content_frame"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />
        <!-- The navigation drawer -->
        <ListView android:id="@+id/left_drawer"
            android:layout_width="240dp"
            android:layout_height="match_parent"
            android:layout_gravity="start"
            android:choiceMode="singleChoice"
            android:divider="@android:color/transparent"
            android:dividerHeight="0dp"
            android:background="#111"/>
    </android.support.v4.widget.DrawerLayout>

</RelativeLayout>

drawer_listview_item.xml

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/title"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_toRightOf="@id/icon"
        android:gravity="center_vertical"
        android:paddingRight="40dp"/>

</LinearLayout>

我收到了一个空指针指针异常。 谁能帮我查明错误？

Answer 1

更改

mDrawerList.setAdapter(new ArrayAdapter<String>(this,R.layout.activity_main,
                R.layout.drawer_listview_item, mPlanetTitles));

至

mDrawerList.setAdapter(new ArrayAdapter<String>(this,R.layout.drawer_listview_item,
                R.id.title, mPlanetTitles));

因为您的列表的自定义布局是drawer_listview_item列表drawer_listview_item ，而不是activity_main

有关更多信息，请参见第6节@ Vogella教程