andriod的简单用法1

public void Login(View view) {
        Intent intent = new Intent();
        //设置从Relativeactivity跳转到LoginActivity
        intent.setClass(Relativeactivity.this, LoginActivity.class);
        //用putExtra来从一个Activity向另一个来传递数据
        intent.putExtra("name", "独此一家");
        intent.putExtra("password", "1234");
        startActivity(intent);
    }

    private EditText loginNameEditText = null;
    private EditText loginPasswordEditText = null;
    
    protected void onCreate(Bundle savedInstanceBundle) {
        super.onCreate(savedInstanceBundle);
        
        setContentView(layout.login);
        
        //requestWindowFeature(Window.FEATURE_NO_TITLE);
        loginNameEditText = (EditText)findViewById(R.id.LoginName);
        loginPasswordEditText = (EditText)findViewById(R.id.LoginPassword);
        //接到传递过来的Intent 
        Intent intent = getIntent();
        //接收Intent中的数据
        String nameString = intent.getStringExtra("name");
        String passwordString = intent.getStringExtra("password");
        loginNameEditText.setText(nameString);
        loginPasswordEditText.setText(passwordString);
                    
        
    }

public void Login(View view) {
        
        String loginNameString = loginNameEditText.getText().toString();
        String loginPasswordString  = loginPasswordEditText.getText().toString();
        Log.d("LoginActivity", loginNameString);
        //判断是否为空用equals
        if(loginNameString.equals(""))
        {
            //这个提示是显示一下自动就消失了
            Toast.makeText(LoginActivity.this, "请输入用户名", Toast.LENGTH_SHORT).show();
            return;
        }
        else {
            Toast.makeText(LoginActivity.this, "已经有了", Toast.LENGTH_SHORT).show();
        }
        if(loginPasswordString.equals(""))
        {
            //这个是alert提示框，可以设置 标题、内容和按钮，不要忘了最后的show
            new AlertDialog.Builder(view.getContext()).setTitle("提示").setMessage("密码不能为空！")
            .setPositiveButton("确定", null).show();
        }
        
        
    }