Question

错误是： - 由以下引起：java.lang.NullPointerException：尝试在com的空对象引用上调用虚方法'void android.support.v7.app.ActionBar.setTitle（java.lang.CharSequence）' .example.pratikrathi.registerapp.MainActivity.onCreate（MainActivity.java:49）

如何解决这个问题？为什么我收到此错误？帮助我

public class MainActivity extends AppCompatActivity {

public Button register_button;
private FirebaseAuth mAuth;




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

    mAuth = FirebaseAuth.getInstance();

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    // Create the adapter that will return a fragment for each of the three
    // primary sections of the activity.
    getSupportActionBar().setTitle("RegisterApp");


}

@Override
protected void onStart() {
    super.onStart();
    FirebaseUser currentUser = FirebaseAuth.getInstance().getCurrentUser();
    if (currentUser == null) {

        sendToLogin();


    }
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}


@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    switch (item.getItemId()){

        case R.id.action_logout_btn:
            logOut();
            return true;
        case R.id.action_settings_btn:
            Intent settingsIntent = new Intent(MainActivity.this,SetupActivity.class);
            startActivity(settingsIntent);

            return true;
    }
    return super.onOptionsItemSelected(item);
}
private void sendToLogin() {
    Intent loginIntent = new Intent(MainActivity.this,LoginActivity.class);
    startActivity(loginIntent);
    finish();
}

private void logOut() {

    mAuth.signOut();
    sendToLogin();

}
}

Xml布局文件包含在下面。

     <?xml version="1.0" encoding="utf-8"?>
     <android.support.design.widget.CoordinatorLayout 
     xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto"
     xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/main_content"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context="com.example.pratikrathi.registerapp.MainActivity">

   <android.support.v7.widget.Toolbar
     android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@color/colorPrimary"
    app:title="RegisterApp">

</android.support.v7.widget.Toolbar>

 </android.support.design.widget.CoordinatorLayout>

Answer 1

尝试像这样设置工具栏标题，并检查您的工具栏ID

Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    // Create the adapter that will return a fragment for each of the three
    // primary sections of the activity.
ActionBar actionBar = getSupportActionBar();
        actionBar.setDisplayHomeAsUpEnabled(true);
    actionBar.setTitle("RegisterApp");

尝试调用虚函数

1 个答案: