我有不同的活动，扩展了BaseActivity。当我点击按钮时：
public class Item1Activity extends BaseActivity {
Button button1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
button1 = (Button) findViewById(R.id.button1);
/**
* We will not use setContentView in this activity
* Rather than we will use layout inflater to add view in FrameLayout of our base activity layout*/
/**
* Adding our layout to parent class frame layout.
*/
getLayoutInflater().inflate(R.layout.activity_main, frameLayout);
button1.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
Intent intent = new Intent(
android.content.Intent.ACTION_VIEW,
Uri.parse("http://maps.google.com/maps?daddr=46.0796808,13.2393894,17z"));
startActivity(intent);
}
});
当我启动应用程序时，它会因NullPointerException而崩溃。 这是日志：
12-09 08:30:44.305: E/AndroidRuntime(740): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
12-09 08:30:44.305: E/AndroidRuntime(740): at com.navigation.drawer.activity.Item1Activity.onCreate(Item1Activity.java:30)
我的基本活动是：
public class BaseActivity extends Activity {
/**
* Frame layout: Which is going to be used as parent layout for child activity layout.
* This layout is protected so that child activity can access this
* */
protected FrameLayout frameLayout;
/**
* ListView to add navigation drawer item in it.
* We have made it protected to access it in child class. We will just use it in child class to make item selected according to activity opened.
*/
protected ListView mDrawerList;
/**
* List item array for navigation drawer items.
* */
protected String[] listArray = { "Item 1", "Item 2", "Item 3", "Item 4", "Item 5" };
/**
* Static variable for selected item position. Which can be used in child activity to know which item is selected from the list.
* */
protected static int position;
/**
* This flag is used just to check that launcher activity is called first time
* so that we can open appropriate Activity on launch and make list item position selected accordingly.
* */
private static boolean isLaunch = true;
/**
* Base layout node of this Activity.
* */
private DrawerLayout mDrawerLayout;
/**
* Drawer listner class for drawer open, close etc.
*/
private ActionBarDrawerToggle actionBarDrawerToggle;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.navigation_drawer_base_layout);
frameLayout = (FrameLayout)findViewById(R.id.content_frame);
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, listArray));
mDrawerList.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
openActivity(position);
}
});
// enable ActionBar app icon to behave as action to toggle nav drawer
getActionBar().setDisplayHomeAsUpEnabled(true);
getActionBar().setHomeButtonEnabled(true);
// ActionBarDrawerToggle ties together the the proper interactions between the sliding drawer and the action bar app icon
actionBarDrawerToggle = new ActionBarDrawerToggle(
this, /* host Activity */
mDrawerLayout, /* DrawerLayout object */
R.drawable.ic_launcher, /* nav drawer image to replace 'Up' caret */
R.string.open_drawer, /* "open drawer" description for accessibility */
R.string.close_drawer) /* "close drawer" description for accessibility */
{
@Override
public void onDrawerClosed(View drawerView) {
getActionBar().setTitle(listArray[position]);
invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
super.onDrawerClosed(drawerView);
}
@Override
public void onDrawerOpened(View drawerView) {
getActionBar().setTitle(getString(R.string.app_name));
invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
super.onDrawerOpened(drawerView);
}
@Override
public void onDrawerSlide(View drawerView, float slideOffset) {
super.onDrawerSlide(drawerView, slideOffset);
}
@Override
public void onDrawerStateChanged(int newState) {
super.onDrawerStateChanged(newState);
}
};
mDrawerLayout.setDrawerListener(actionBarDrawerToggle);
/**
* As we are calling BaseActivity from manifest file and this base activity is intended just to add navigation drawer in our app.
* We have to open some activity with layout on launch. So we are checking if this BaseActivity is called first time then we are opening our first activity.
* */
if(isLaunch){
/**
*Setting this flag false so that next time it will not open our first activity.
*We have to use this flag because we are using this BaseActivity as parent activity to our other activity.
*In this case this base activity will always be call when any child activity will launch.
*/
isLaunch = false;
openActivity(0);
}
}
/**
* @param position
*
* Launching activity when any list item is clicked.
*/
protected void openActivity(int position) {
/**
* We can set title & itemChecked here but as this BaseActivity is parent for other activity,
* So whenever any activity is going to launch this BaseActivity is also going to be called and
* it will reset this value because of initialization in onCreate method.
* So that we are setting this in child activity.
*/
mDrawerList.setItemChecked(position, true);
setTitle(listArray[position]);
mDrawerLayout.closeDrawer(mDrawerList);
BaseActivity.position = position;
switch (position) {
case 0:
startActivity(new Intent(this, Item1Activity.class));
break;
case 1:
startActivity(new Intent(this, Item2Activity.class));
break;
case 2:
startActivity(new Intent(this, Item3Activity.class));
break;
case 3:
startActivity(new Intent(this, Item4Activity.class));
break;
case 4:
startActivity(new Intent(this, Item5Activity.class));
break;
default:
break;
}
Toast.makeText(this, "Selected Item Position::"+position, Toast.LENGTH_LONG).show();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main, menu);
return super.onCreateOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// The action bar home/up action should open or close the drawer.
// ActionBarDrawerToggle will take care of this.
if (actionBarDrawerToggle.onOptionsItemSelected(item)) {
return true;
}
switch (item.getItemId()) {
case R.id.action_settings:
return true;
default:
return super.onOptionsItemSelected(item);
}
}
/* Called whenever we call invalidateOptionsMenu() */
@Override
public boolean onPrepareOptionsMenu(Menu menu) {
// If the nav drawer is open, hide action items related to the content view
boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
menu.findItem(R.id.action_settings).setVisible(!drawerOpen);
return super.onPrepareOptionsMenu(menu);
}
/* We can override onBackPressed method to toggle navigation drawer*/
@Override
public void onBackPressed() {
if(mDrawerLayout.isDrawerOpen(mDrawerList)){
mDrawerLayout.closeDrawer(mDrawerList);
}else {
mDrawerLayout.openDrawer(mDrawerList);
}
}
}
答案 0 :(得分：0)
按钮定义在哪里？如果它在R.layout.activity_main，那么你应该先膨胀，然后尝试找到按钮。更改您的代码：
第一：
getLayoutInflater().inflate(R.layout.activity_main, frameLayout);
第二：
button1 = (Button) findViewById(R.id.button1);
这应该可以解决问题。