我正在尝试为我的应用实现抽屉导航,但我似乎无法启动它,我无法弄清楚为什么。它在setAdapter返回一个空指针异常,但我不明白,因为这是复制和过去几乎来自android和其他类似的教程。谁能告诉我我做错了什么?
主要活动
import android.app.Activity;
import android.os.Bundle;
import android.support.v4.widget.DrawerLayout;
import android.util.Log;
import android.view.Menu;
import android.widget.ArrayAdapter;
import android.widget.ListView;
public class MainActivity extends Activity {
private String[] mContentTitles;
private DrawerLayout mDrawerLayout;
private ListView mDrawerList;
private final String TAG = "MainActivity";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mContentTitles = getResources().getStringArray(R.array.contentTitles);
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
mDrawerList = (ListView) findViewById(R.id.left_drawer);
mDrawerList.setAdapter(new ArrayAdapter<String>(this, R.layout.drawer_list_item, mContentTitles));
}
@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;
}
}
DrawerLayout.xml
<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:background="#111"
android:choiceMode="singleChoice"
android:divider="@android:color/transparent"
android:dividerHeight="0dp" />
</android.support.v4.widget.DrawerLayout>
drawer_list_item.xml
<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@android:id/text1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textColor="#fff"
android:textSize="20sp"
android:gravity="center_vertical"
android:paddingStart="14.5sp"
android:paddingEnd="14.5sp"
android:minHeight="35sp"
/>
的strings.xml
<?xml version="1.0" encoding="utf-8"?>
<string name="app_name">FrontRowReady</string>
<string name="action_settings">Settings</string>
<string name="home">Home</string>
<string name="settings">Settings</string>
<string name="inbox">Inbox</string>
<string name="contacts">Contacts</string>
<array name="contentTitles">
<item>Home</item>
<item>Inbox</item>
<item>Contacts</item>
<item>Settings</item>
</array>
错误代码
12-23 14:29:11.315:E / AndroidRuntime(30524):致命异常:主要 12-23 14:29:11.315:E / AndroidRuntime(30524):处理:PID:30524 12-23 14:29:11.315:E / AndroidRuntime(30524):java.lang.RuntimeException:无法启动活动java.lang.NullPointerException 12-23 14:29:11.315:E / AndroidRuntime(30524):在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195) 12-23 14:29:11.315:E / AndroidRuntime(30524):在android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245) 12-23 14:29:11.315:E / AndroidRuntime(30524):在android.app.ActivityThread.access $ 800(ActivityThread.java:135) 12-23 14:29:11.315:E / AndroidRuntime(30524):在android.app.ActivityThread $ H.handleMessage(ActivityThread.java:1196) 12-23 14:29:11.315:E / AndroidRuntime(30524):在android.os.Handler.dispatchMessage(Handler.java:102) 12-23 14:29:11.315:E / AndroidRuntime(30524):在android.os.Looper.loop(Looper.java:136) 12-23 14:29:11.315:E / AndroidRuntime(30524):在android.app.ActivityThread.main(ActivityThread.java:5017) 12-23 14:29:11.315:E / AndroidRuntime(30524):at java.lang.reflect.Method.invokeNative(Native Method) 12-23 14:29:11.315:E / AndroidRuntime(30524):at java.lang.reflect.Method.invoke(Method.java:515) 12-23 14:29:11.315:E / AndroidRuntime(30524):at com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:779) 12-23 14:29:11.315:E / AndroidRuntime(30524):at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 12-23 14:29:11.315:E / AndroidRuntime(30524):at dalvik.system.NativeStart.main(Native Method) 12-23 14:29:11.315:E / AndroidRuntime(30524):引起:java.lang.NullPointerException 12-23 14:29:11.315:E / AndroidRuntime(30524):at com.maxxpotential.frontrowready.MainActivity.onCreate(MainActivity.java:27) 12-23 14:29:11.315:E / AndroidRuntime(30524):在android.app.Activity.performCreate(Activity.java:5231) 12-23 14:29:11.315:E / AndroidRuntime(30524):在android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087) 12-23 14:29:11.315:E / AndroidRuntime(30524):在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159) 12-23 14:29:11.315:E / AndroidRuntime(30524):... 11更多
答案 0 :(得分:9)
更改此部分代码:
setContentView(R.layout.activity_main);
到此:
setContentView(R.layout.DrawerLayout);
答案 1 :(得分:2)
我有点好奇您的内容视图:
setContentView(R.layout.activity_main);
你的R.layout.activity_main
是什么?它是否包含您的抽屉布局?如果没有,
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
将导致mDrawerLayout为空。
答案 2 :(得分:1)
您说您的XML名为DrawerLayout.xml
,但您将内容设置为:
setContentView(R.layout.activity_main);
您需要将内容指定为包含布局的文件:
setContentView(R.layout.DrawerLayout);
答案 3 :(得分:1)
navigationView.getHeaderView(0).findViewById(R.id.SOME_ID);