andorid 计算器

avtivity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<GridLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:rowCount="6"
    android:columnCount="4"
    >
    <!--rowCount   行数
    columnCount   列数
    layout_columnSpan    跨列
    layout_rowSpan      跨行
    fill_horizontal   水平填充
    fill_vertical    垂直填充
    layout_columnWeight   权重列
    layout_rowWeight   权重行
    background  @drawable/  设置图片
    layout_row 指定行号
    layout_column  指定列好  从0开始
    -->
    <EditText
        android:layout_columnSpan="4"
        android:layout_gravity="fill_horizontal"
        android:layout_columnWeight="1"
        android:layout_rowWeight="1"
        android:editable="false"
        android:gravity="right|center_vertical"
        android:id="@+id/et"/>

    <Button
        android:text="清除"
        android:layout_columnWeight="1"
        android:layout_rowWeight="1"
        android:textSize="25sp"
        android:id="@+id/clear"
        />
    <Button
        android:text="后退"
        android:layout_columnWeight="1"
        android:layout_rowWeight="1"
        android:textSize="25sp"
        android:id="@+id/goback"/>

    <Button
        android:text="/"
        android:layout_columnWeight="1"
        android:layout_rowWeight="1"
        android:textSize="25sp"/>
    <Button
        android:text="X"
        android:layout_columnWeight="1"
        android:layout_rowWeight="1"
        android:textSize="25sp"/>
    <Button
        android:text="7"
        android:layout_columnWeight="1"
        android:layout_rowWeight="1"
        android:textSize="25sp"
        android:id="@+id/bt_7"/>
    <Button
        android:text="8"
        android:layout_columnWeight="1"
        android:layout_rowWeight="1"
        android:textSize="25sp"
        android:id="@+id/bt_8"/>
    <Button
        android:text="9"
        android:layout_columnWeight="1"
        android:layout_rowWeight="1"
        android:textSize="25sp"
        android:id="@+id/bt_9"/>
    <Button
        android:text="-"
        android:layout_columnWeight="1"
        android:layout_rowWeight="1"
        android:textSize="25sp"/>
    <Button
        android:text="4"
        android:layout_columnWeight="1"
        android:layout_rowWeight="1"
        android:textSize="25sp"/>
    <Button
        android:text="5"
        android:layout_columnWeight="1"
        android:layout_rowWeight="1"
        android:textSize="25sp"/>
    <Button
        android:text="6"
        android:layout_columnWeight="1"
        android:layout_rowWeight="1"
        android:textSize="25sp"/>
    <Button
        android:text="+"
        android:layout_columnWeight="1"
        android:layout_rowWeight="1"
        android:textSize="25sp"/>
    <Button
        android:text="1"
        android:layout_columnWeight="1"
        android:layout_rowWeight="1"
        android:textSize="25sp"/>
    <Button
        android:text="2"
        android:layout_columnWeight="1"
        android:layout_rowWeight="1"
        android:textSize="25sp"/>
    <Button
        android:text="3"
        android:layout_columnWeight="1"
        android:layout_rowWeight="1"
        android:textSize="25sp"/>
    <Button
        android:text="="
        android:layout_rowSpan="2"
        android:layout_gravity="fill_vertical"
        android:layout_columnWeight="1"
        android:layout_rowWeight="2"
        android:textSize="25sp"
        android:background="#24f"
        />
    <Button
        android:text="0"
        android:layout_columnSpan="2"
        android:layout_gravity="fill_horizontal"
        android:layout_columnWeight="2"
        android:layout_rowWeight="1"
        android:textSize="25sp"
        />
    <Button
        android:text="."
        android:layout_columnWeight="1"
        android:layout_rowWeight="1"
        android:textSize="25sp"
        />

</GridLayout>

CalculatorActivity

package com.hanqi.application3;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

/**
 * Created by Administrator on 2016/3/28.
 */
public class CalculatorActivity extends Activity implements View.OnClickListener {
    EditText et;
    Button  bt_clear;
    Button  bt_goback;
    Button  bt_7;
    Button  bt_8;
    Button  bt_9;
    //构建字符串StringBuffer
    //存储显示的内容
    private StringBuffer str_show= new StringBuffer();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.avtivity_main);

        et=(EditText)findViewById(R.id.et);
        bt_clear=(Button)findViewById(R.id.clear);
        bt_7=(Button)findViewById(R.id.bt_7);
        bt_8=(Button)findViewById(R.id.bt_8);
        bt_9=(Button)findViewById(R.id.bt_9);

        bt_clear.setOnClickListener(this);
        bt_goback.setOnClickListener(this);
        bt_7.setOnClickListener(this);
        bt_8.setOnClickListener(this);
        bt_9.setOnClickListener(this);

    }

    public void onClick(View v)
    {
        Button bt = (Button)v;

        int id =bt.getId();
        switch (id)
        {
            case R.id.clear:
                str_show= new StringBuffer();
                et.setText(str_show);
                break;
            case R.id.goback:
                str_show.codePointAt(str_show.length()-1);
                et.setText(str_show);
                break;
            case R.id.bt_7:
            case R.id.bt_8:
            case R.id.bt_9:
                str_show.append(bt.getText());
                et.setText(str_show);
                break;

        }
    }
}