[Android开发学习21]写一个简单的乘法计算器，并添加退出菜单

一、目标和即将学到的知识:

1.目标:

写一个简单的乘法计算器，并添加退出菜单

2.即将需要或者学习到的知识:

①.TextView显示文本

②.EditText编辑框

③.Button按钮

④.Menu菜单

3.基础知识:

① setText函数中，连接符两端，有一个端是字符串，则另外一端也会被转为字符串。

[java]
private TextView resultView;
private int result;
...
resultView.setText(result + "");

private TextView resultView;
private int result;
...
resultView.setText(result + "");

② 判断某字符串是否为空:

if(factorOneStr.equals(""))

③ 字符串转整数:

int factorOneInt = Integer.parseInt(factorOneStr);

④ 添加菜单:

为主程序添加菜单显示: onCreateOptionsMenu(重载函数)
为菜单添加响应事件: onOptionsItemSelected(重载函数)

[java]
@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // TODO Auto-generated method stub
    if(item.getItemId()==1){
        finish();   // 结束当前Activity.
    }
    return super.onOptionsItemSelected(item);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // TODO Auto-generated method stub
    menu.add(0,1,1,R.string.exit);
    menu.add(0,2,2,R.string.about);
    return super.onCreateOptionsMenu(menu);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
  // TODO Auto-generated method stub
  if(item.getItemId()==1){
   finish(); // 结束当前Activity.
  }
  return super.onOptionsItemSelected(item);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
  // TODO Auto-generated method stub
  menu.add(0,1,1,R.string.exit);
  menu.add(0,2,2,R.string.about);
  return super.onCreateOptionsMenu(menu);
}

3.用到的快捷键:

添加导入库 Ctrl+Shift+M

二、代码展示:

1."Activity_03\src\yan\activity_02\Activity_03.java"

[java]
package yan.activity_03;

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

/*
* 1.在Activity_03当中，要声明四个控件
* 2.要为其中的两个控件设置显示的值
* 3.创建一个易做图类，监听按钮按下的动作
* 4.将易做图类的对象，绑定在按钮对象上
* */
public class Activity_03 extends Activity {
    private EditText factorOne;
    private EditText factorTwo;
    private TextView symbol;
    private Button calculate;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_03);
        //根据控件的ID来取得代表控件的对象
        factorOne = (EditText)findViewById(R.id.factorOne);
        factorTwo = (EditText)findViewById(R.id.factorTwo);
        symbol = (TextView)findViewById(R.id.symbol);
        calculate = (Button)findViewById(R.id.calculate);
        // 为symbol和calculate设置显示的值
        symbol.setText(R.string.symbol);
        calculate.setText(R.string.calculate);
        // 将易做图的对象绑定到按钮对象上面
        calculate.setOnClickListener(new CalculateListener());
    }


    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // TODO Auto-generated method stub
        if(item.getItemId()==1){
            finish();   // 结束当前Activity.
        }
        return super.onOptionsItemSelected(item);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // TODO Auto-generated method stub
        menu.add(0,1,1,R.string.exit);
        menu.add(0,2,2,R.string.about);
        return super.onCreateOptionsMenu(menu);
    }

    class CalculateListener implements OnClickListener{

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            // 取得两个EditText控件的值
            String factorOneStr = factorOne.getText().toString();
            String factorTwoStr = factorTwo.getText().toString();
            // 将这两个值存放到Intent对象中
            Intent intent = new Intent();
            intent.putExtra("one", factorOneStr);
            intent.putExtra("two", factorTwoStr);
            intent.setClass(Activity_03.this, ResultActivity.class);
            // 使用这个Intent对象来启动R

补充：移动开发 , Android ,