将 EditText 添加到警报对话框。

我有以下创建警报对话框的代码，并向其中添加了两个编辑文本，但是一旦运行应用程序，将不会检索 EditText 中的值，并且我的应用程序会因 NullPointerException 崩溃：

代码是：

AlertDialog.Builder alert = new AlertDialog.Builder(this);
        LayoutInflater inflater=this.getLayoutInflater();
        final EditText usernameInput=(EditText)findViewById(R.id.dialogusername);
        final EditText passwordInput=(EditText)findViewById(R.id.dialogpassword);   
        alert.setView(inflater.inflate(R.layout.dialog,null));
        alert.setTitle("Enter Password");
        alert.setMessage("Enter password to remove the app:");
        alert.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int whichButton) {
            //provide user with caution before uninstalling
            //also here should be added a AsyncTask that going to read the password and once its checked the password is correct the app will be removed
            value1=usernameInput.getText().toString();
            value2=passwordInput.getText().toString();
            if(value1.equals(null)&&value2.equals(null))
            {Toast.makeText(context, "Enter username and password", Toast.LENGTH_SHORT).show();}
         }
        });
        });
        alert.show();

感谢大家在回答我的问题时做出的贡献，我想我得到了上面发布的问题的解决方案，即：

AlertDialog.Builder alert = new AlertDialog.Builder(MyFeedActivity.this);
        LayoutInflater inflater=MyFeedActivity.this.getLayoutInflater();
        //this is what I did to added the layout to the alert dialog
        View layout=inflater.inflate(R.layout.dialog,null);       
        alert.setView(layout);
        final EditText usernameInput=(EditText)layout.findViewById(R.id.dialogusername);
        final EditText passwordInput=(EditText)layout.findViewById(R.id.dialogpassword);

我认为问题是我无法在警报对话框中获取 EidtText，但是通过上面的代码，每件事对我来说都工作得很好。