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android老师布置的课程作业——简单计算器
功能要求实现四则运算，参考界面见下图：
首先给各位老铁提供apk安装包以及项目压缩包，略表诚意~
github地址：https://github.com/wonke/calculator
使用girdlayout比较适合计算器这种规则的布局，每行有几个按钮几乎都是固定的，遇到一个按钮需要占两个常规按钮空间时，使用android:layout_columnspan="2"属性即可解决。
layout布局代码：
我要评论<?xml version="1.0" encoding="utf-8"?>
<linearlayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".mainactivity">
<textview
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:height="30dp"
android:gravity="center"
android:text="@string/title"
android:textappearance="@style/textappearance.appcompat.large" />
<gridlayout
android:id="@+id/grid_layout"
android:layout_width="match_parent"
android:layout_height="500sp"
android:background="#ece7e7"
android:alignmentmode="alignbounds"
android:columncount="4"
android:orientation="horizontal"
android:rowcount="10"
android:usedefaultmargins="false">
<textview
android:id="@+id/contenttext"
android:background="@drawable/textview_border"
android:gravity="end"
android:textsize="50sp"
android:layout_columnspan="4"
android:layout_columnweight="1"
android:layout_rowweight="5"
/>
<button
android:id="@+id/allclear"
android:textsize="30sp"
android:background="@drawable/button_border"
android:layout_rowweight="1"
android:layout_columnweight="1"
android:text="ce" />
<button
android:id="@+id/divide"
android:textsize="30sp"
android:background="@drawable/button_border"
android:layout_rowweight="1"
android:layout_columnweight="1"
android:text="÷" />
<button
android:id="@+id/multiply"
android:layout_rowweight="1"
android:layout_columnweight="1"
android:background="@drawable/button_border"
android:text="×"
android:textsize="30sp" />
<button
android:id="@+id/clear"
android:layout_rowweight="1"
android:layout_columnweight="1"
android:background="@drawable/button_border"
android:text="c"
android:textsize="30sp" />
<button
android:id="@+id/b7"
android:layout_rowweight="1"
android:layout_columnweight="1"
android:background="@drawable/button_border"
android:text="7"
android:textsize="30sp" />
<button
android:id="@+id/b8"
android:layout_rowweight="1"
android:layout_columnweight="1"
android:background="@drawable/button_border"
android:text="8"
android:textsize="30sp" />
<button
android:id="@+id/b9"
android:layout_rowweight="1"
android:layout_columnweight="1"
android:background="@drawable/button_border"
android:text="9"
android:textsize="30sp" />
<button
android:id="@+id/add"
android:layout_rowweight="1"
android:layout_columnweight="1"
android:background="@drawable/button_border"
android:text="+"
android:textsize="30sp" />
<button
android:id="@+id/b4"
android:layout_rowweight="1"
android:layout_columnweight="1"
android:background="@drawable/button_border"
android:text="4"
android:textsize="30sp" />
<button
android:id="@+id/b5"
android:layout_rowweight="1"
android:layout_columnweight="1"
android:background="@drawable/button_border"
android:text="5"
android:textsize="30sp" />
<button
android:id="@+id/b6"
android:layout_rowweight="1"
android:layout_columnweight="1"
android:background="@drawable/button_border"
android:text="6"
android:textsize="30sp" />
<button
android:id="@+id/subtract"
android:layout_rowweight="1"
android:layout_columnweight="1"
android:background="@drawable/button_border"
android:text="-"
android:textsize="30sp" />
<button
android:id="@+id/b1"
android:layout_rowweight="1"
android:layout_columnweight="1"
android:background="@drawable/button_border"
android:text="1"
android:textsize="30sp" />
<button
android:id="@+id/b2"
android:layout_rowweight="1"
android:layout_columnweight="1"
android:background="@drawable/button_border"
android:text="2"
android:textsize="30sp" />
<button
android:id="@+id/b3"
android:layout_rowweight="1"
android:layout_columnweight="1"
android:background="@drawable/button_border"
android:text="3"
android:textsize="30sp" />
<button
android:id="@+id/root"
android:layout_rowweight="1"
android:layout_columnweight="1"
android:background="@drawable/button_border"
android:text="√￣"
android:textsize="30sp" />
<button
android:id="@+id/b0"
android:layout_rowweight="1"
android:layout_columnspan="2"
android:layout_columnweight="1"
android:background="@drawable/button_border"
android:text="0"
android:textsize="30sp" />
<button
android:id="@+id/point"
android:layout_rowweight="1"
android:layout_columnweight="1"
android:background="@drawable/button_border"
android:text="."
android:textsize="30sp" />
<button
android:id="@+id/equal"
android:layout_rowweight="1"
android:layout_columnweight="1"
android:background="@drawable/button_border"
android:text="="
android:textsize="30sp" />
</gridlayout>
</linearlayout>
mainactivity逻辑处理代码：
import android.support.v7.app.appcompatactivity;
import android.os.bundle;
import android.view.view;
import android.widget.button;
import android.widget.textview;
public class mainactivity extends appcompatactivity implements view.onclicklistener {
private button[] buttons = new button[18];
private int[] ids = new int[]{r.id.allclear,r.id.divide,r.id.multiply,r.id.clear,r.id.b0,r.id.b1,
r.id.b2,r.id.b3,r.id.b4,r.id.b5,r.id.b6,r.id.b7,r.id.b8,r.id.b9,r.id.add,r.id.subtract,
r.id.equal,r.id.point};
private textview textview;
private string expression = "";
private boolean end = false;
private int countoperate=2;
@override
protected void oncreate(bundle savedinstancestate) {
super.oncreate(savedinstancestate);
setcontentview(r.layout.activity_main);
for (int i=0; i<ids.length;i++){
buttons[i] = findviewbyid(ids[i]);
buttons[i].setonclicklistener(this);
}
textview = (textview)findviewbyid(r.id.contenttext);
}
public void onclick(view view) {
int id = view.getid();
button button = (button)view.findviewbyid(id);
string current = button.gettext().tostring();
if(end){ //如果上一次算式已经结束，则先清零
expression = "";
end = false;
}
if(current.equals("ce")){ //如果为ce则清零
expression = "";
countoperate=0;
}else if(current.equals("c")){ //如果点击退格
if(expression.length()>1){ //算式长度大于1
expression = expression.substring(0,expression.length()-1);//退一格
int i = expression.length()-1;
char tmp = expression.charat(i); //获得最后一个字符
char tmpfront = tmp;
for(;i>=0;i--){ //向前搜索最近的 +-*/和.，并退出
tmpfront = expression.charat(i);
if(tmpfront=='.'||tmpfront=='+'||tmpfront=='-'||tmpfront=='×'||tmpfront=='÷'){
break;
}
}
if(tmp>='0'&&tmp<='9'){ //最后一个字符为数字，则识别数赋值为0
countoperate=0;
}else if(tmp==tmpfront&&tmpfront!='.') countoperate=2; //如果为+-*/，赋值为2
else if(tmpfront=='.') countoperate=1; //如果前面有小数点赋值为1
}else if(expression.length()==1){
expression = "";
}
}else if(current.equals(".")){
if(expression.equals("")||countoperate==2){
expression+="0"+current;
countoperate = 1; //小数点按过之后赋值为1
}
if(countoperate==0){
expression+=".";
countoperate = 1;
}
}else if(current.equals("+")||current.equals("-")||current.equals("×")||current.equals("÷")){
if(countoperate==0){
expression+=current;
countoperate = 2; // +-*/按过之后赋值为2
}
}else if(current.equals("=")){ //按下=时，计算结果并显示
double result = (double) math.round(count()*100)/100;
expression+="="+result;
end = true; //此次计算结束
}
else{//此处是当退格出现2+0时，用current的值替代0
if(expression.length()>=1){
char tmp1 = expression.charat(expression.length()-1);
if(tmp1=='0'&&expression.length()==1){
expression = expression.substring(0,expression.length()-1);
}
else if(tmp1=='0'&&expression.length()>1){
char tmp2 = expression.charat(expression.length()-2);
if(tmp2=='+'||tmp2=='-'||tmp2=='×'||tmp2=='÷'){
expression = expression.substring(0,expression.length()-1);
}
}
}
expression+=current;
if(countoperate==2||countoperate==1) countoperate=0;
}
// toast.maketext(this, "countoperate:"+countoperate, toast.length_short).show();
textview.settext(expression); //显示出来
}
//计算逻辑，求expression表达式的值
private double count(){
double result=0;
double tnum=1,lownum=0.1,num=0;
char tmp=0;
int operate = 1; //识别+-*/，为+时为正数，为-时为负数，为×时为-2/2,为/时为3/-3;
boolean point = false;
for(int i=0;i<expression.length();i++){ //遍历表达式
tmp = expression.charat(i);
if(tmp=='.'){ //因为可能出现小数，此处进行判断是否有小数出现
point = true;
lownum = 0.1;
}else if(tmp=='+'||tmp=='-'){
if(operate!=3&&operate!=-3){ //此处判断通用，适用于+-*
tnum *= num;
}else{ //计算/
tnum /= num;
}
// toast.maketext(this, "tnum = "+tnum, toast.length_short).show();
if(operate<0){ //累加入最终的结果
result -= tnum;
}else{
result += tnum;
}
operate = tmp=='+'?1:-1;
num = 0;
tnum = 1;
point = false;
}else if(tmp=='×'){
if(operate!=3&&operate!=-3){
tnum *= num;
}else{
tnum /= num;
}
operate = operate<0?-2:2;
point = false;
num = 0;
}else if(tmp=='÷'){
if(operate!=3&&operate!=-3){
tnum *= num;
}else{
tnum /= num;
}
operate = operate<0?-3:3;
point = false;
num = 0;
}else{
//读取expression中的每个数字，doube型
if(!point){
num = num*10+tmp-'0';
}else{
num += (tmp-'0')*lownum;
lownum*=0.1;
}
}
}
//循环遍历结束，计算最后一个运算符后面的数
if(operate!=3&&operate!=-3){
tnum *= num;
}else{
tnum /= num;
}
// toast.maketext(this, "tnum = "+tnum, toast.length_short).show();
if(operate<0){
result -= tnum;
}else{
result += tnum;
}
//返回最后的结果
return result;
}
}
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