Android开发中requestfocus()无效的原因及解决办法

package com.example.hfs.requestfocusdemo;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
 private EditText mUserName,mPassWord;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  initView();
 }
 private void initView() {
  mUserName= (EditText) this.findViewById(R.id.et_username);
  mPassWord= (EditText) this.findViewById(R.id.et_password);
  mPassWord.setOnClickListener(this);
 }
 @Override
 public void onClick(View view) {
  if (!"123456".equals(mPassWord.getText().toString())){
   Toast.makeText(this,"密码错误,请重新输入",Toast.LENGTH_SHORT).show();
   mPassWord.requestFocus();
  }else{
   startActivity(new Intent(this,MainActivity.class));
   Toast.makeText(this,"登陆成功",Toast.LENGTH_SHORT).show();
   finish();
  }
 }
}

mPassWord.postDelayed(new Runnable() { 
　　@Override 
　　public void run() { 
　　　　mPassWord.requestFocus(); 
　　} 
}, 500); 

setVisible(true); 
person.requestFocus();