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：
<?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;
}}
