android意图数据使用if（！bundle.getString（“ ACCOUNT”）。equals（null））但出错

Question

我做一个Android页面。在此页面中有一些产品目录。客户可以查找产品，如果要购买，可以按订购按钮。如果客户未登录。它将跳转到登录页面。

但是当我将登录页面添加到目录页面时，会给我一个错误。我该怎么办？
  这是我的代码MainActivity.java

public class MainActivity extends Activity {
   ArrayList<Team> teams = new ArrayList<Team>();
    ListView listview;
    String account="";
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

        Intent intent=this.getIntent();
        Bundle bundle=intent.getExtras();
        if(!bundle.getString("ACCOUNT").equals(null) ){
            account=bundle.getString("ACCOUNT");
           }
     listview = (ListView) findViewById(R.id.listview);
     listview.setOnItemClickListener(lvonclick);
      String result =dbcourse.executeQuery();
     Team team =new Team("my_product","price");
     teams.add(team);
      team = new Team("fish", "77");
      teams.add(team); 
          final TeamsAdapter adapter = new TeamsAdapter(this, R.layout.team, teams);
            listview.setAdapter(adapter);
   }

         private ListView.OnItemClickListener lvonclick=
                    new ListView.OnItemClickListener(){
                    @Override
                    public void onItemClick(AdapterView<?> parent, View v,
                            int position, long id) {
                        String sel=parent.getItemAtPosition(position).toString();   
                     mydialog(sel);

                    }
                };

private void mydialog(String str1){
    new AlertDialog.Builder(MainActivity.this)
    .setTitle("product")
    .setIcon(R.drawable.ic_launcher)
    .setMessage(str1)
    .setPositiveButton("buy", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialoginterface, int i)
        {
            if(account==""){
                Intent intent2=new Intent();//jump to login page
            intent2.setClass(MainActivity.this,Login.class);
            startActivity(intent2);
            }
            else{mytoast("success");}
        }
    })
    .show(); 
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
  getMenuInflater().inflate(R.menu.main, menu);
    return true;
}
}

login.java：

public class Login extends Activity {//登入畫面
 private TextView acc,pwd;
 private  Button  btn;
 @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.login);
      StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder()             
     acc=(TextView)findViewById(R.id.acc);
     pwd=(TextView)findViewById(R.id.pwd);
     btn=(Button)findViewById(R.id.btn);
     btn.setOnClickListener(btnlogin);


}

private Button.OnClickListener btnlogin=new Button.OnClickListener(){
    public void onClick(View v){
        String account=acc.getText().toString();
        String passwd=pwd.getText().toString();
            Intent intent= new Intent();
                intent.setClass(Login.this, MainActivity.class);
                Bundle bundle=new Bundle();
                if(account=="123")
                {
                  bundle.putString("ACCOUNT", account);
                  intent.putExtras(bundle);
                  startActivity(intent);
                }
    }
};
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}
}

Answer 1

我认为您上面提到的if（！bundle.getString（“ ACCOUNT”）。equals（null））方法是错误的检查方法。我总是喜欢这样

 if (intent != null && intent.getExtras() != null) {
                mCurrentUser = new User();
                mCurrentUser.setmEmail(intent.getExtras().getString(Email));

            }

Answer 2

正常的检查登录逻辑如下所示

但是你的逻辑是 MainActivity -> LoginActivity (login success) -> (start a new) MainActivity 您有两个MainActivity。

这是代码演示

MainActivity {

  dialogButtonClick{
    //startActivityForResult() go to LoginActivity
  }

  onActivityResult() {
    //check result here
  }

}

LoginActivity {

 loginButtonClick() {
    //login success
    //setResultCode
    //set ACCOUNT info to the intent
    //finish() current activity
 }

}

如果您不了解startActivityForResult()和onActivityResult()逻辑，请参考文档click here