在这个程序中，我实现了sliding library。实现这个库，我正在尝试创建一个 MenuActivity 类来处理所有菜单项滑块选项，onClick监听器等。现在这个类看起来像这样：
public class MenuActivity extends SlidingActivity{
SharePrefManager sm = new SharePrefManager(MenuActivity.this);
RelativeLayout ask_a_question, life_prediction;
TextView aries,taurus,gemini,cancer,leo,virgo,libra,scorpio,sagittarius,capricon,aquarius,pisces;
String isLoggedIn;
@Override
public void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setBehindContentView(R.layout.menu);
ask_a_question = (RelativeLayout)findViewById(R.id.ask_a_question);
HashMap<String, String> checkLogin = new HashMap<String, String>();
checkLogin = sm.getuserDetails();
isLoggedIn = checkLogin.get(SharePrefManager.KEY_ISLOGEDIN);
ask_a_question.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
if (isLoggedIn.equals(0))
{
Toast.makeText(getApplicationContext(), "You must be logged in", Toast.LENGTH_SHORT).show();
}
else
{
Intent i = new Intent("com.example.btshome.ASKPAGE");
startActivity(i);
}
}
});
}
}
这个类基本上是实现库并设置滑动菜单项和onClick事件处理程序。该类还访问首选项，以检查用户是否已登录。
在我的 MainActivity 类中，我正在扩展此类并尝试从中获取功能。
public class MainActivity extends MenuActivity{
Button login;
@Override
public void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
login = (Button)findViewById(R.id.log_in_button);
login.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
startActivity(new Intent("com.example.btshome.LOGINACTIVITY"));
}
});
}
}
在以下实现中，发生以下错误：
04-24 10:46:45.081: E/AndroidRuntime(1956): FATAL EXCEPTION: main
04-24 10:46:45.081: E/AndroidRuntime(1956): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.btshome/com.example.btshome.MainActivity}: java.lang.NullPointerException
04-24 10:46:45.081: E/AndroidRuntime(1956): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1983)
04-24 10:46:45.081: E/AndroidRuntime(1956): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
04-24 10:46:45.081: E/AndroidRuntime(1956): at android.app.ActivityThread.access$600(ActivityThread.java:130)
04-24 10:46:45.081: E/AndroidRuntime(1956): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
04-24 10:46:45.081: E/AndroidRuntime(1956): at android.os.Handler.dispatchMessage(Handler.java:99)
04-24 10:46:45.081: E/AndroidRuntime(1956): at android.os.Looper.loop(Looper.java:137)
04-24 10:46:45.081: E/AndroidRuntime(1956): at android.app.ActivityThread.main(ActivityThread.java:4745)
04-24 10:46:45.081: E/AndroidRuntime(1956): at java.lang.reflect.Method.invokeNative(Native Method)
04-24 10:46:45.081: E/AndroidRuntime(1956): at java.lang.reflect.Method.invoke(Method.java:511)
04-24 10:46:45.081: E/AndroidRuntime(1956): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
04-24 10:46:45.081: E/AndroidRuntime(1956): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
04-24 10:46:45.081: E/AndroidRuntime(1956): at dalvik.system.NativeStart.main(Native Method)
04-24 10:46:45.081: E/AndroidRuntime(1956): Caused by: java.lang.NullPointerException
04-24 10:46:45.081: E/AndroidRuntime(1956): at android.content.ContextWrapper.getSharedPreferences(ContextWrapper.java:153)
04-24 10:46:45.081: E/AndroidRuntime(1956): at com.example.btshome.library.SharePrefManager.<init>(SharePrefManager.java:35)
04-24 10:46:45.081: E/AndroidRuntime(1956): at com.example.btshome.MenuActivity.<init>(MenuActivity.java:17)
04-24 10:46:45.081: E/AndroidRuntime(1956): at com.example.btshome.MainActivity.<init>(MainActivity.java:14)
04-24 10:46:45.081: E/AndroidRuntime(1956): at java.lang.Class.newInstanceImpl(Native Method)
04-24 10:46:45.081: E/AndroidRuntime(1956): at java.lang.Class.newInstance(Class.java:1319)
04-24 10:46:45.081: E/AndroidRuntime(1956): at android.app.Instrumentation.newActivity(Instrumentation.java:1053)
04-24 10:46:45.081: E/AndroidRuntime(1956): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1974)
04-24 10:46:45.081: E/AndroidRuntime(1956): ... 11 more
那么这里出了什么问题？是 MenuActivity 类吗？我是否以不同的方式解决这个问题？