Question

我尝试将数据从MainActivity发送到TimeActivity，但TimeActivity中收到的包是null。当我不放

时抛出空指针异常

s = extras.getString("key");

中的

if (extras != null) {

 }

和一条消息说＆＃34;该应用程序不幸停止＆＃34;。但是在按OK之后，TimeActivity开始，并在

中接收值125

String s;

这是MainActivity。

public class MainActivity extends AppCompatActivity {
SharedPreferences sharedpreferences;
TextView name;
TextView email;
public static final String mypreference = "mypref";
public static final String Name = "nameKey";
public static final String Email = "emailKey";
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    name = (TextView) findViewById(R.id.etName);
    Button btn = (Button) findViewById(R.id.button1);
    btn.setOnClickListener(new View.OnClickListener() {
                               @Override
                               public void onClick(View v) {

                                   String n = name.getText().toString();
                                   String e = "1";
                                   SharedPreferences.Editor editor = sharedpreferences.edit();
                                   editor.putString(Name, n);

                                   editor.commit();
                                    if(n.length()==3){
                                   Intent intent = new Intent(MainActivity.this, TimeActivity.class);
                                   startActivity(intent);}else{
                                        Toast.makeText(MainActivity.this,"The Roll Number Must be a 3 Digit number",Toast.LENGTH_LONG).show();
                                    }
                               }
                           }

    );


        sharedpreferences=

        getSharedPreferences(mypreference,
                             Context.MODE_PRIVATE);

        if(sharedpreferences.contains(Name))

        {
            String s = sharedpreferences.getString(Name, "");
            Intent i = new Intent(getApplicationContext(), TimeActivity.class);
            i.putExtra("key", s);
            startActivity(i);

        }

        else

        {

        }


    }



}

这是TimeActivity

   public class TimeActivity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_time);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    toolbar.setTitle("Timely");setSupportActionBar(toolbar);

String s="0";
    Bundle extras = getIntent().getExtras();
    if (extras != null) {

        Intent i = new Intent(getApplicationContext(), TimeActivity.class);
        startActivity(i);s = extras.getString("key");
    }else{Toast.makeText(TimeActivity.this,"Bundle received Null. ",Toast.LENGTH_LONG).show();}
int r  = Integer.parseInt(s);
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
            this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
    drawer.setDrawerListener(toggle);
    toggle.syncState();
    NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(this);
}

@Override
public void onBackPressed() {
System.exit(0);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.time, 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.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
    // Handle navigation view item clicks here.
    int id = item.getItemId();

    if (id == R.id.nav_home) {

    } else if (id == R.id.nav_timetable) {

    } else if (id == R.id.nav_about) {
        startActivity(new Intent(TimeActivity.this, About.class));
    } else if (id == R.id.nav_Develop) {

    } else if (id == R.id.nav_share) {

    } else if (id == R.id.nav_send) {

    }


    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    drawer.closeDrawer(GravityCompat.START);
    return true;
}

}

任何形式的帮助都将受到赞赏。

Answer 1

我可以在这里看到两个可能的问题。

首先，您没有通过MainActivity

中的Bundle

Intent intent = new Intent(MainActivity.this, TimeActivity.class);
startActivity(intent);

其次，您在TimeActivity方法中再次启动onCreate()。

if (extras != null) {
    Intent i = new Intent(getApplicationContext(), TimeActivity.class);
    startActivity(i);
    s = extras.getString("key");
}

空指针异常：捆绑意图。 Bundle收到null。但它后来仍然显示出价值

1 个答案: