Question

我是Android的初学者并遇到问题我正在尝试从登录活动的登录按钮打开主要活动时显示以上错误。

当按下登录按钮时，应用程序停止并显示以下错误

在android监视器中显示以下错误

10-20 18:47:23.314 13432-13432/com.antherx.prasenjit.ihdfbachatgat E/AndroidRuntime: FATAL EXCEPTION: main
 Process: com.antherx.prasenjit.ihdfbachatgat, PID: 13432
 java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.antherx.prasenjit.ihdfbachatgat/com.antherx.prasenjit.ihdfbachatgat.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2460)
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2629)
     at android.app.ActivityThread.access$800(ActivityThread.java:182)
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1474)
     at android.os.Handler.dispatchMessage(Handler.java:111)
     at android.os.Looper.loop(Looper.java:194)
     at android.app.ActivityThread.main(ActivityThread.java:5706)
     at java.lang.reflect.Method.invoke(Native Method)
     at java.lang.reflect.Method.invoke(Method.java:372)
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1033)
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:828)
  Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
     at android.content.ContextWrapper.getPackageName(ContextWrapper.java:132)
     at android.content.ComponentName.<init>(ComponentName.java:77)
     at android.content.Intent.<init>(Intent.java:4358)
     at com.antherx.prasenjit.ihdfbachatgat.MainActivity.<init>(MainActivity.java:26)
     at java.lang.reflect.Constructor.newInstance(Native Method)
     at java.lang.Class.newInstance(Class.java:1606)
     at android.app.Instrumentation.newActivity(Instrumentation.java:1071)
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2437)
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2629) 
     at android.app.ActivityThread.access$800(ActivityThread.java:182) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1474) 
     at android.os.Handler.dispatchMessage(Handler.java:111) 
     at android.os.Looper.loop(Looper.java:194) 
     at android.app.ActivityThread.main(ActivityThread.java:5706) 
     at java.lang.reflect.Method.invoke(Native Method) 
     at java.lang.reflect.Method.invoke(Method.java:372) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1033) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:828)

这是登录活动代码是他们在此代码中的任何问题

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_login);
    //Please do not

    Email = (EditText)findViewById(R.id.email);
    Password = (EditText)findViewById(R.id.password);
    String wel_on_login = "Welcome On IHDF Bachat Gat app";
    Toast welcome = Toast.makeText(getApplicationContext(),wel_on_login,Toast.LENGTH_LONG);
    welcome.show();

    final Button signIn = (Button)findViewById(R.id.email_sign_in_button);
    final Button register = (Button)findViewById(R.id.registration) ;
    final Intent main_trans = new Intent(this, MainActivity.class);
    final Intent reg_trans = new Intent(this, register.class);

    signIn.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View view) {

            startActivity(main_trans);
        }
    });

    register.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            startActivity(reg_trans);
        }
    });

这是主要的活动代码是他们在这里的任何问题

 protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    toolbar = (Toolbar)findViewById(R.id.home_toolbar);
    setSupportActionBar(toolbar);
    newMember = (MenuItem)findViewById(R.id.new_member);
    newProfile = (MenuItem)findViewById(R.id.profile) ;

    Drawer =(DrawerLayout)findViewById(R.id.drawerLayout);
    sToggle = new ActionBarDrawerToggle(this,Drawer,R.string.open,R.string.close);


    Grp_ico = (ImageView)findViewById(R.id.grp_ico);

    Drawer.addDrawerListener(sToggle);
    sToggle.syncState();

    getSupportActionBar();


    String wel_on_main = "You are successfully on Main Home";
    Toast welcome = Toast.makeText(getApplicationContext(),wel_on_main,Toast.LENGTH_LONG);
    welcome.show();




}

@Override
public boolean onOptionsItemSelected(MenuItem item) {

    switch (item.getItemId()){

        case R.id.new_member :
            startActivity(new_new_member);
        case R.id.profile :
            startActivity(new_new_profile);
        case R.id.setting :
            startActivity(new_new_setting);
        case R.id.meeting :
            startActivity(new_new_meeting);
            default:
                return super.onOptionsItemSelected(item);


    }

}

Answer 1

对我来说，我试图在没有基本上下文的情况下使用该应用程序。

所以我在我的应用程序覆盖：

@Override
    protected void attachBaseContext(Context newBase) {
}

//instead of calling its super:

 @Override
    protected void attachBaseContext(Context newBase) {
        super.attachBaseContext(newBase);}

Answer 2

从

更改

[account]
user=user1
pass=pass1

[account]
user=user2
pass=pass2

[account]
user=user3
pass=pass3
expdate=2016

getApplicationContext()

到Toast welcome = Toast.makeText(getApplicationContext(),wel_on_main,Toast.LENGTH_LONG);或最好是getBaseContext()

空对象引用

2 个答案: