我的 MainActivity 类中有一个方法,我可以从不同的 Activity 类访问该方法,以便为所有其他 Activity 实例化应用程序栏中的选项卡。
然而,当我从一个类调用 MainActivity 类中的这个函数时,它抛出了一个 java.lang.NullPointerException
:
我在 MainActivity.Java
中的函数
public void initiateMenuTabs(ActionBar actionBar) {
try {
actionBar.setDisplayShowTitleEnabled(false);
actionBar.setDisplayUseLogoEnabled(true);
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
ActionBar.TabListener tabListener = new ActionBar.TabListener() {
@Override
public void onTabUnselected(Tab arg0, FragmentTransaction arg1) {
// TODO Auto-generated method stub
}
@Override
public void onTabSelected(Tab tab, FragmentTransaction arg1) {
int tabPosition = tab.getPosition();
switch (tabPosition) {
case 0:
setContentView(R.layout.event_feed);
break;
case 1: {
Intent startClassActivity = new Intent(MainActivity.this,
ClassWide.class);
startActivity(startClassActivity);
break;
}
case 2:
setContentView(R.layout.event_feed);
break;
}
}
@Override
public void onTabReselected(Tab arg0, FragmentTransaction arg1) {
// TODO Auto-generated method stub
}
};
actionBar.addTab(actionBar.newTab().setText("Event Feed")
.setIcon(R.drawable.ic_action_alarms)
.setTabListener(tabListener));
actionBar.addTab(actionBar.newTab().setText("Wide")
.setIcon(R.drawable.ic_action_Wide)
.setTabListener(tabListener));
actionBar.addTab(actionBar.newTab().setText("Report")
.setIcon(R.drawable.ic_action_location_found)
.setTabListener(tabListener));
} catch (Exception e) {
Log.getStackTraceString(e.getCause().getCause());
}
}
从 ClassWide.Java
调用函数
protected void onCreate(final Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.wide_view);
MainActivity cObj = new MainActivity();
cObj.initiateMenuTabs(getActionBar());
.... ....
LogCat
窗口显示如下:
09-29 15:21:09.217: E/AndroidRuntime(2549): FATAL EXCEPTION: main
09-29 15:21:09.217: E/AndroidRuntime(2549): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.helloworld.projectone/com.helloworld.projectone.ClassWide}: java.lang.NullPointerException
09-29 15:21:09.217: E/AndroidRuntime(2549): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
09-29 15:21:09.217: E/AndroidRuntime(2549): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
09-29 15:21:09.217: E/AndroidRuntime(2549): at android.app.ActivityThread.access$600(ActivityThread.java:141)
09-29 15:21:09.217: E/AndroidRuntime(2549): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
09-29 15:21:09.217: E/AndroidRuntime(2549): at android.os.Handler.dispatchMessage(Handler.java:99)
09-29 15:21:09.217: E/AndroidRuntime(2549): at android.os.Looper.loop(Looper.java:137)
09-29 15:21:09.217: E/AndroidRuntime(2549): at android.app.ActivityThread.main(ActivityThread.java:5103)
09-29 15:21:09.217: E/AndroidRuntime(2549): at java.lang.reflect.Method.invokeNative(Native Method)
09-29 15:21:09.217: E/AndroidRuntime(2549): at java.lang.reflect.Method.invoke(Method.java:525)
09-29 15:21:09.217: E/AndroidRuntime(2549): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
09-29 15:21:09.217: E/AndroidRuntime(2549): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
09-29 15:21:09.217: E/AndroidRuntime(2549): at dalvik.system.NativeStart.main(Native Method)
09-29 15:21:09.217: E/AndroidRuntime(2549): Caused by: java.lang.NullPointerException
09-29 15:21:09.217: E/AndroidRuntime(2549): at com.helloworld.projectone.MainActivity.initiateMenuTabs(MainActivity.java:79)
09-29 15:21:09.217: E/AndroidRuntime(2549): at com.helloworld.projectone.ClassWide.onCreate(ClassWide.java:21)
09-29 15:21:09.217: E/AndroidRuntime(2549): at android.app.Activity.performCreate(Activity.java:5133)
09-29 15:21:09.217: E/AndroidRuntime(2549): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
09-29 15:21:09.217: E/AndroidRuntime(2549): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
09-29 15:21:09.217: E/AndroidRuntime(2549): ... 11 more
最佳答案
您正在另一个 Activity 中实例化一个 Android Activity 。 Activity 不仅仅是 android 中的一个简单类, 从你想要的任何 Activity 调用你的方法你应该做的是定义你的 BaseActivity,它包含所有 Activity 共有的方法并扩展它而不是扩展一般的 Activity 类:
public class BaseActivity extends Activity {
public void initiateMenuTabs(ActionBar actionBar) {
....//your code
}
}
然后在任何其他需要调用 initiateMenuTabs 方法的 Activity 中扩展您的 BaseActivity
public ClassWide extends BaseActivity{
protected void onCreate(final Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.wide_view);
initiateMenuTabs(getActionBar());// here it will call the method from the parent (BaseActivity)
.... ....
关于java - actionBar.addTab 抛出 NullPointerException,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/19082126/