Android：集成导航抽屉给出空对象引用错误
Android : Integrating Navigation Drawer giving null object reference error
我正在开发一个 Android 应用程序，我试图在其中集成 Navigation Drawer。现在，该项目分为两个部分，一个是用户，一个是餐厅。两者都是不同的项目，因此它们都有不同的 APK 和全部。
现在，用户的抽屉工作得很好。我对餐厅使用了相同的代码，但它抛出了一个错误。我不知道为什么。所以基本上，我创建了一个抽屉布局 activity 并在 class 中扩展了 activity。无论我想要抽屉在哪里，我都会扩展 DrawerLayoutActivity class，而不是正常的 activity，并在 XML 中添加列表和 android 抽屉布局。它在用户中工作。这是相关代码：
错误日志：
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
at internetlegion.com.restaurantlunchify.RestaurantDrawer.RestaurantDrawerActivity.set(RestaurantDrawerActivity.java:90)
at internetlegion.com.restaurantlunchify.Activity.AddRestaurantImages.onCreate(AddRestaurantImages.java:42)
at android.app.Activity.performCreate(Activity.java:5958)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1129)
RestaurantDrawerActivity
public class RestaurantDrawerActivity extends Activity{
private DrawerLayout mDrawerLayout;
private ListView mDrawerList;
private ActionBarDrawerToggle mDrawerToggle;
// nav drawer title
private CharSequence mDrawerTitle;
// used to store app title
private CharSequence mTitle;
// slide menu items/*
private String[] navMenuTitles;
private TypedArray navMenuIcons;
private ArrayList<DrawerModel> navDrawerItems;
private RestaurantDrawerListAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.restaurant_drawerlayout);
}
public void set(String[] navMenuTitles, TypedArray navMenuIcons) {
mTitle = mDrawerTitle = getTitle();
navMenuTitles = getResources().getStringArray(R.array.restaurant_nav_drawer_items);
navMenuIcons = getResources()
.obtainTypedArray(R.array.nav_drawer_icons);
mDrawerLayout = (DrawerLayout) findViewById(R.id.restaurant_drawer_layout);
mDrawerList = (ListView) findViewById(R.id.restaurant_list_slidermenu);
navDrawerItems = new ArrayList<DrawerModel>();
/*for (int i = 0; i < navMenuTitles.length; i++) {
navDrawerItems.add(new DrawerModel(navMenuTitles[i],
navMenuIcons.getResourceId(i, -1)));
}*/
navDrawerItems.add(new DrawerModel(navMenuTitles[0], navMenuIcons.getResourceId(0, -1)));
// Find People
navDrawerItems.add(new DrawerModel(navMenuTitles[1], navMenuIcons.getResourceId(1, -1)));
// Photos
navDrawerItems.add(new DrawerModel(navMenuTitles[2], navMenuIcons.getResourceId(2, -1)));
// Communities, Will add a counter here
navDrawerItems.add(new DrawerModel(navMenuTitles[3], navMenuIcons.getResourceId(3, -1)));
// Pages
navDrawerItems.add(new DrawerModel(navMenuTitles[4], navMenuIcons.getResourceId(4, -1)));
// What's hot, We will add a counter here
navDrawerItems.add(new DrawerModel(navMenuTitles[5], navMenuIcons.getResourceId(5, -1)));
// Recycle the typed array
navMenuIcons.recycle();
mDrawerList.setOnItemClickListener(new SlideMenuClickListener());
// setting the nav drawer list adapter
adapter = new RestaurantDrawerListAdapter(getApplicationContext(),
navDrawerItems);
mDrawerList.setAdapter(adapter);
// The line below fails
getActionBar().setDisplayHomeAsUpEnabled(true);
getActionBar().setHomeButtonEnabled(true);
mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout,
R.drawable.ic_drawer, //nav menu toggle icon
R.string.app_name, // nav drawer open - description for accessibility
R.string.app_name // nav drawer close - description for accessibility
) {
public void onDrawerClosed(View view) {
getActionBar().setTitle(mTitle);
// calling onPrepareOptionsMenu() to show action bar icons
invalidateOptionsMenu();
}
public void onDrawerOpened(View drawerView) {
getActionBar().setTitle(mDrawerTitle);
// calling onPrepareOptionsMenu() to hide action bar icons
invalidateOptionsMenu();
}
};
mDrawerLayout.setDrawerListener(mDrawerToggle);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// toggle nav drawer on selecting action bar app icon/title
if (mDrawerToggle.onOptionsItemSelected(item)) {
return true;
}
// Handle action bar actions click
switch (item.getItemId()) {
case R.id.action_settings:
return true;
default:
return super.onOptionsItemSelected(item);
}
}
@Override
public void setTitle(CharSequence title) {
mTitle = title;
getActionBar().setTitle(mTitle);
}
/**
* When using the ActionBarDrawerToggle, you must call it during
* onPostCreate() and onConfigurationChanged()...
*/
@Override
protected void onPostCreate(Bundle savedInstanceState) {
super.onPostCreate(savedInstanceState);
// Sync the toggle state after onRestoreInstanceState has occurred.
mDrawerToggle.syncState();
}
@Override
public void onConfigurationChanged(Configuration newConfig) {
super.onConfigurationChanged(newConfig);
// Pass any configuration change to the drawer toggls
mDrawerToggle.onConfigurationChanged(newConfig);
}
/* *
* Called when invalidateOptionsMenu() is triggered
*/
@Override
public boolean onPrepareOptionsMenu(Menu menu) {
// if nav drawer is opened, hide the action items
boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
menu.findItem(R.id.action_settings).setVisible(!drawerOpen);
return super.onPrepareOptionsMenu(menu);
}
/**
* Slide menu item click listener
* */
private class SlideMenuClickListener implements
ListView.OnItemClickListener {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position,
long id) {
// display view for selected nav drawer item
displayView(position);
}
}
}
我是这样使用它的：
public class AddRestaurantImages extends RestaurantDrawerActivity {
private static final int CAMERA_PIC_REQUEST = 22;
Button BtnSelectImage;
private ImageView ImgPhoto;
Bitmap photo;
int menucardid;
RestaurantServiceImpl restaurantService = new RestaurantServiceImpl();
private String[] navMenuTitles;
private TypedArray navMenuIcons;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
navMenuTitles = getResources().getStringArray(R.array.restaurant_nav_drawer_items);
navMenuIcons = getResources()
.obtainTypedArray(R.array.nav_drawer_icons);
set(navMenuTitles, navMenuIcons);
那么，到底哪里出了问题。任何帮助都会很好。非常感谢。 :-)
更新 XML 必要文件柜:
<android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/restaurant_drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent">
<LinearLayout 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:gravity="top|center"
android:orientation="vertical"
tools:context=".MainActivity">
<Button
android:id="@+id/BtnSelectImg"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Insert Image" />
<Button
android:id="@+id/uploadImageButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:text="Upload restImage" />
<ImageView
android:id="@+id/ImgPhoto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:src="@drawable/ic_launcher" />
<Button
android:id="@+id/up"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Upload Image" />
</LinearLayout>
<ListView
android:id="@+id/restaurant_list_slidermenu"
android:layout_width="240dp"
android:layout_height="match_parent"
android:layout_gravity="start"
android:choiceMode="singleChoice"
android:dividerHeight="1dp" />
</android.support.v4.widget.DrawerLayout>
您尝试在未设置操作栏的情况下调用操作栏上的 setDisplayHomeAsUpEnabled(boolean) 函数。
我建议只为工具栏创建一个新布局。这是一个使用支持库的示例。
toolbar.xml
<android.support.v7.widget.Toolbar xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:elevation="4dp"
android:background="?attr/colorPrimary"
app:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />
修改属性以满足您的需要。
在下一步中，您将此布局包含在 restaurant_drawerlayout.xml 文件中，如下所示：
<include layout="@layout/toolbar" />
这样您就可以在所有布局中使用相同的工具栏布局文件。
然后在您的 set(String[] navMenuTitles, TypedArray navMenuIcons) 中执行以下操作：
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
这样做之后，您可以使用
获取操作栏
getSupportActionBar()
应该可以了。
我正在开发一个 Android 应用程序，我试图在其中集成 Navigation Drawer。现在，该项目分为两个部分，一个是用户，一个是餐厅。两者都是不同的项目，因此它们都有不同的 APK 和全部。 现在，用户的抽屉工作得很好。我对餐厅使用了相同的代码，但它抛出了一个错误。我不知道为什么。所以基本上，我创建了一个抽屉布局 activity 并在 class 中扩展了 activity。无论我想要抽屉在哪里，我都会扩展 DrawerLayoutActivity class，而不是正常的 activity，并在 XML 中添加列表和 android 抽屉布局。它在用户中工作。这是相关代码：
错误日志：
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
at internetlegion.com.restaurantlunchify.RestaurantDrawer.RestaurantDrawerActivity.set(RestaurantDrawerActivity.java:90)
at internetlegion.com.restaurantlunchify.Activity.AddRestaurantImages.onCreate(AddRestaurantImages.java:42)
at android.app.Activity.performCreate(Activity.java:5958)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1129)
RestaurantDrawerActivity
public class RestaurantDrawerActivity extends Activity{
private DrawerLayout mDrawerLayout;
private ListView mDrawerList;
private ActionBarDrawerToggle mDrawerToggle;
// nav drawer title
private CharSequence mDrawerTitle;
// used to store app title
private CharSequence mTitle;
// slide menu items/*
private String[] navMenuTitles;
private TypedArray navMenuIcons;
private ArrayList<DrawerModel> navDrawerItems;
private RestaurantDrawerListAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.restaurant_drawerlayout);
}
public void set(String[] navMenuTitles, TypedArray navMenuIcons) {
mTitle = mDrawerTitle = getTitle();
navMenuTitles = getResources().getStringArray(R.array.restaurant_nav_drawer_items);
navMenuIcons = getResources()
.obtainTypedArray(R.array.nav_drawer_icons);
mDrawerLayout = (DrawerLayout) findViewById(R.id.restaurant_drawer_layout);
mDrawerList = (ListView) findViewById(R.id.restaurant_list_slidermenu);
navDrawerItems = new ArrayList<DrawerModel>();
/*for (int i = 0; i < navMenuTitles.length; i++) {
navDrawerItems.add(new DrawerModel(navMenuTitles[i],
navMenuIcons.getResourceId(i, -1)));
}*/
navDrawerItems.add(new DrawerModel(navMenuTitles[0], navMenuIcons.getResourceId(0, -1)));
// Find People
navDrawerItems.add(new DrawerModel(navMenuTitles[1], navMenuIcons.getResourceId(1, -1)));
// Photos
navDrawerItems.add(new DrawerModel(navMenuTitles[2], navMenuIcons.getResourceId(2, -1)));
// Communities, Will add a counter here
navDrawerItems.add(new DrawerModel(navMenuTitles[3], navMenuIcons.getResourceId(3, -1)));
// Pages
navDrawerItems.add(new DrawerModel(navMenuTitles[4], navMenuIcons.getResourceId(4, -1)));
// What's hot, We will add a counter here
navDrawerItems.add(new DrawerModel(navMenuTitles[5], navMenuIcons.getResourceId(5, -1)));
// Recycle the typed array
navMenuIcons.recycle();
mDrawerList.setOnItemClickListener(new SlideMenuClickListener());
// setting the nav drawer list adapter
adapter = new RestaurantDrawerListAdapter(getApplicationContext(),
navDrawerItems);
mDrawerList.setAdapter(adapter);
// The line below fails
getActionBar().setDisplayHomeAsUpEnabled(true);
getActionBar().setHomeButtonEnabled(true);
mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout,
R.drawable.ic_drawer, //nav menu toggle icon
R.string.app_name, // nav drawer open - description for accessibility
R.string.app_name // nav drawer close - description for accessibility
) {
public void onDrawerClosed(View view) {
getActionBar().setTitle(mTitle);
// calling onPrepareOptionsMenu() to show action bar icons
invalidateOptionsMenu();
}
public void onDrawerOpened(View drawerView) {
getActionBar().setTitle(mDrawerTitle);
// calling onPrepareOptionsMenu() to hide action bar icons
invalidateOptionsMenu();
}
};
mDrawerLayout.setDrawerListener(mDrawerToggle);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// toggle nav drawer on selecting action bar app icon/title
if (mDrawerToggle.onOptionsItemSelected(item)) {
return true;
}
// Handle action bar actions click
switch (item.getItemId()) {
case R.id.action_settings:
return true;
default:
return super.onOptionsItemSelected(item);
}
}
@Override
public void setTitle(CharSequence title) {
mTitle = title;
getActionBar().setTitle(mTitle);
}
/**
* When using the ActionBarDrawerToggle, you must call it during
* onPostCreate() and onConfigurationChanged()...
*/
@Override
protected void onPostCreate(Bundle savedInstanceState) {
super.onPostCreate(savedInstanceState);
// Sync the toggle state after onRestoreInstanceState has occurred.
mDrawerToggle.syncState();
}
@Override
public void onConfigurationChanged(Configuration newConfig) {
super.onConfigurationChanged(newConfig);
// Pass any configuration change to the drawer toggls
mDrawerToggle.onConfigurationChanged(newConfig);
}
/* *
* Called when invalidateOptionsMenu() is triggered
*/
@Override
public boolean onPrepareOptionsMenu(Menu menu) {
// if nav drawer is opened, hide the action items
boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
menu.findItem(R.id.action_settings).setVisible(!drawerOpen);
return super.onPrepareOptionsMenu(menu);
}
/**
* Slide menu item click listener
* */
private class SlideMenuClickListener implements
ListView.OnItemClickListener {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position,
long id) {
// display view for selected nav drawer item
displayView(position);
}
}
}
我是这样使用它的：
public class AddRestaurantImages extends RestaurantDrawerActivity {
private static final int CAMERA_PIC_REQUEST = 22;
Button BtnSelectImage;
private ImageView ImgPhoto;
Bitmap photo;
int menucardid;
RestaurantServiceImpl restaurantService = new RestaurantServiceImpl();
private String[] navMenuTitles;
private TypedArray navMenuIcons;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
navMenuTitles = getResources().getStringArray(R.array.restaurant_nav_drawer_items);
navMenuIcons = getResources()
.obtainTypedArray(R.array.nav_drawer_icons);
set(navMenuTitles, navMenuIcons);
那么，到底哪里出了问题。任何帮助都会很好。非常感谢。 :-)
更新 XML 必要文件柜:
<android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/restaurant_drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent">
<LinearLayout 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:gravity="top|center"
android:orientation="vertical"
tools:context=".MainActivity">
<Button
android:id="@+id/BtnSelectImg"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Insert Image" />
<Button
android:id="@+id/uploadImageButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:text="Upload restImage" />
<ImageView
android:id="@+id/ImgPhoto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:src="@drawable/ic_launcher" />
<Button
android:id="@+id/up"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Upload Image" />
</LinearLayout>
<ListView
android:id="@+id/restaurant_list_slidermenu"
android:layout_width="240dp"
android:layout_height="match_parent"
android:layout_gravity="start"
android:choiceMode="singleChoice"
android:dividerHeight="1dp" />
</android.support.v4.widget.DrawerLayout>
您尝试在未设置操作栏的情况下调用操作栏上的 setDisplayHomeAsUpEnabled(boolean) 函数。
我建议只为工具栏创建一个新布局。这是一个使用支持库的示例。
toolbar.xml
<android.support.v7.widget.Toolbar xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:elevation="4dp"
android:background="?attr/colorPrimary"
app:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />
修改属性以满足您的需要。
在下一步中，您将此布局包含在 restaurant_drawerlayout.xml 文件中，如下所示：
<include layout="@layout/toolbar" />
这样您就可以在所有布局中使用相同的工具栏布局文件。
然后在您的 set(String[] navMenuTitles, TypedArray navMenuIcons) 中执行以下操作：
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
这样做之后，您可以使用
获取操作栏getSupportActionBar()
应该可以了。