Android仿微信或支付宝方块密码输入框

import android.app.Activity; 
import android.os.Bundle; 
import android.text.Editable; 
import android.text.TextWatcher; 
import android.widget.EditText; 
import android.widget.TextView; 
 
public class MainActivity extends Activity { 
 
  TextView t1, t2, t3, t4, et; 
 
  String key = ""; 
 
  @Override 
  protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.verifycode); 
    t1 = (TextView) findViewById(R.id.t1); 
    t2 = (TextView) findViewById(R.id.t2); 
    t3 = (TextView) findViewById(R.id.t3); 
    t4 = (TextView) findViewById(R.id.t4); 
    et = (EditText) findViewById(R.id.editText1); 
    et.addTextChangedListener(tw); 
  } 
 
  void setKey() { 
    char[] arr = key.toCharArray(); 
    t1.setText(""); 
    t2.setText(""); 
    t3.setText(""); 
    t4.setText(""); 
    for (int i = 0; i < arr.length; i++) { 
      if (i == 0) { 
        t1.setText(String.valueOf(arr[0])); 
      } else if (i == 1) { 
        t2.setText(String.valueOf(arr[1])); 
      } else if (i == 2) { 
        t3.setText(String.valueOf(arr[2])); 
      } else if (i == 3) { 
        t4.setText(String.valueOf(arr[3])); 
      } 
    } 
  } 
 
  TextWatcher tw = new TextWatcher() { 
    @Override 
    public void onTextChanged(CharSequence s, int start, int before, 
        int count) { 
 
    } 
 
    @Override 
    public void beforeTextChanged(CharSequence s, int start, int count, 
        int after) { 
 
    } 
 
    @Override 
    public void afterTextChanged(Editable s) { 
      key = s.toString(); 
      setKey(); 
    } 
  }; 
} 

final AlertDialog dialog = new AlertDialog.Builder(mContext).create(); 
   dialog.show(); 
   dialog.getWindow().setContentView(R.layout.verifycode);t1 = (TextView) dialog.findViewById(R.id.t1); 
   t2 = (TextView) dialog.findViewById(R.id.t2); 
   t3 = (TextView) dialog.findViewById(R.id.t3); 
   t4 = (TextView) dialog.findViewById(R.id.t4);