所以我在项目的第33行得到了Null Pointer错误,但我不知道它是什么。任何帮助将不胜感激。
06-15 21:15:24.813: E/AndroidRuntime(15696): java.lang.RuntimeException: Unable to start activiy
ComponentInfo{yc.android.yourchallenger/yc.android.yourchallenger.MainActivity}: java.lang.NullPointerException
06-15 21:15:24.813: E/AndroidRuntime(15696): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2308)
06-15 21:15:24.813: E/AndroidRuntime(15696): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2362)
06-15 21:15:24.813: E/AndroidRuntime(15696): at android.app.ActivityThread.access$700(ActivityThread.java:168)
06-15 21:15:24.813: E/AndroidRuntime(15696): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1329)
06-15 21:15:24.813: E/AndroidRuntime(15696): at android.os.Handler.dispatchMessage(Handler.java:99)
06-15 21:15:24.813: E/AndroidRuntime(15696): at android.os.Looper.loop(Looper.java:137)
06-15 21:15:24.813: E/AndroidRuntime(15696): at android.app.ActivityThread.main(ActivityThread.java:5493)
06-15 21:15:24.813: E/AndroidRuntime(15696): at java.lang.reflect.Method.invokeNative(Native Method)
06-15 21:15:24.813: E/AndroidRuntime(15696): at java.lang.reflect.Method.invoke(Method.java:525)
06-15 21:15:24.813: E/AndroidRuntime(15696): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1209)
06-15 21:15:24.813: E/AndroidRuntime(15696): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1025)
06-15 21:15:24.813: E/AndroidRuntime(15696): at dalvik.system.NativeStart.main(Native Method)
06-15 21:15:24.813: E/AndroidRuntime(15696): Caused by: java.lang.NullPointerException
06-15 21:15:24.813: E/AndroidRuntime(15696): at yc.android.yourchallenger.MainActivity.onCreate(MainActivity.java:33)
06-15 21:15:24.813: E/AndroidRuntime(15696): at android.app.Activity.performCreate(Activity.java:5372)
06-15 21:15:24.813: E/AndroidRuntime(15696): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1104)
06-15 21:15:24.813: E/AndroidRuntime(15696): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2270)
06-15 21:15:24.813: E/AndroidRuntime(15696): ... 11 more
以下是我收到错误的MainActivity 包yc.android.yourchallenger;
import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentManager;
import android.os.Bundle;
import android.support.v4.app.ActionBarDrawerToggle;
import android.support.v4.widget.DrawerLayout;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.ListView;
public class MainActivity extends Activity {
private String [] mNavigationDrawerItemTitles;
private DrawerLayout mDrawerLayout;
private ListView mDrawerList;
ActionBarDrawerToggle mDrawerToggle;
private CharSequence mDrawerTitle;
private CharSequence mTitle;
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mNavigationDrawerItemTitles = getResources().getStringArray(R.array.navigation_drawer_items_array);
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.nav_drawer, mNavigationDrawerItemTitles));
// Set the list's click listener
mDrawerList.setOnItemClickListener((OnItemClickListener) new DrawerItemClickListener());
}
private class DrawerItemClickListener implements ListView.OnItemClickListener {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
selectItem(position);
}
}
private void selectItem(int position) {
Fragment fragment = new CreateFragment();
Bundle args = new Bundle();
args.putInt("key", position);
fragment.setArguments(args);
FragmentManager fragmentManager = getFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.content_frame, fragment)
.commit();
// Highlight the selected item, update the title, and close the drawer
mDrawerList.setItemChecked(position, true);
setTitle(mNavigationDrawerItemTitles[position]);
mDrawerLayout.closeDrawer(mDrawerList);
}
@Override
public void setTitle(CharSequence title){
mTitle = title;
getActionBar().setTitle(mTitle);
}
}
答案 0 :(得分:1)
确保您的活动的布局包含带有android:id="@+id/left_drawer"
的ListView,否则对findViewById()
的调用将返回null。
答案 1 :(得分:0)
正如我在评论中所建议的那样,请确保ListView
内有activity_main layout
名为 left_drawer 的内容。否则,您无法使用findViewById()
调用它。
您没有向mNavigationDrawerItemTitles
字符串数组添加任何值,而是将其添加到适配器中。也称为setOnItemClickListener()
。但是列表中没有值。因为您的mNavigationDrawerItemTitles
是空的。将一些值添加到字符串数组并进行测试。