Android Studio实现简单计算器APP

<?xml version="1.0" encoding="utf-8"?>
<GridLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:tools="http://schemas.android.com/tools"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:layout_below="@ id/textView"
 android:layout_alignParentStart="true"
 android:rowCount="6"
 android:columnCount="4"
 > <!--设置网格为6行4列-->
 <!--显示文本组件，占1行4列-->
 <TextView
 android:id="@ id/text"
 android:layout_width="350dp"
 android:layout_height="wrap_content"
 android:layout_columnSpan="4"
 android:layout_marginLeft="4px"
 android:gravity="left"
 android:textSize="50dp" />
 
 <!--清除按钮，占1行4列-->
 <Button
 android:id="@ id/btnClear"
 android:layout_width="353dp"
 android:layout_height="wrap_content"
 android:layout_columnSpan="4"
 android:text="清除"
 android:textSize="26sp" />
 
 <!--以下按钮为数字按钮和函数按钮，每个占1行1列-->
 <Button
 android:id="@ id/btn1"
 android:text="1"
 android:textSize="26sp" />
 <Button
 android:id="@ id/btn2"
 android:text="2"
 android:textSize="26sp" />
 <Button
 android:id="@ id/btn3"
 android:text="3"
 android:textSize="26sp" />
 <Button
 android:id="@ id/btnPlus"
 android:text=" "
 android:textSize="26sp" />
 <Button
 android:id="@ id/btn4"
 android:text="4"
 android:textSize="26sp" />
 <Button
 android:id="@ id/btn5"
 android:text="5"
 android:textSize="26sp" />
 <Button
 android:id="@ id/btn6"
 android:text="6"
 android:textSize="26sp" />
 <Button
 android:id="@ id/btnSubtract"
 android:text="-"
 android:textSize="26sp" />
 <Button
 android:id="@ id/btn7"
 android:text="7"
 android:textSize="26sp" />
 <Button
 android:id="@ id/btn8"
 android:text="8"
 android:textSize="26sp" />
 <Button
 android:id="@ id/btn9"
 android:text="9"
 android:textSize="26sp" />
 <Button
 android:id="@ id/btnMultiply"
 android:text="*"
 android:textSize="26sp" />
 <Button
 android:id="@ id/btnPoint"
 android:text="."
 android:textSize="26sp" />
 <Button
 android:id="@ id/btn0"
 android:text="0"
 android:textSize="26sp" />
 <Button
 android:id="@ id/btnSum"
 android:text="="
 android:textSize="26sp" />
 <Button
 android:id="@ id/btnDivide"
 android:text="/"
 android:textSize="26sp" />
 
</GridLayout>

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
 
 Button btn0,btn1,btn2,btn3,btn4,btn5,btn6,btn7,btn8,btn9,
 btnClear,btnPlus,btnSubtract,btnMultiply,btnDivide,btnSum,btnPoint;
 TextView text;
 String str = "";
 
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 
 btn0 = (Button) findViewById(R.id.btn0);
 btn1 = (Button) findViewById(R.id.btn1);
 btn2 = (Button) findViewById(R.id.btn2);
 btn3 = (Button) findViewById(R.id.btn3);
 btn4 = (Button) findViewById(R.id.btn4);
 btn5 = (Button) findViewById(R.id.btn5);
 btn6 = (Button) findViewById(R.id.btn6);
 btn7 = (Button) findViewById(R.id.btn7);
 btn8 = (Button) findViewById(R.id.btn8);
 btn9 = (Button) findViewById(R.id.btn9);
 btnClear = (Button) findViewById(R.id.btnClear);
 btnPlus = (Button) findViewById(R.id.btnPlus);
 btnSubtract = (Button) findViewById(R.id.btnSubtract);
 btnMultiply = (Button) findViewById(R.id.btnMultiply);
 btnDivide = (Button) findViewById(R.id.btnDivide);
 btnPoint = (Button) findViewById(R.id.btnPoint);
 btnSum = (Button) findViewById(R.id.btnSum);
 
 text = (TextView) findViewById(R.id.text) ;
 
 btn0.setOnClickListener(this);
 btn1.setOnClickListener(this);
 btn2.setOnClickListener(this);
 btn3.setOnClickListener(this);
 btn4.setOnClickListener(this);
 btn5.setOnClickListener(this);
 btn6.setOnClickListener(this);
 btn7.setOnClickListener(this);
 btn8.setOnClickListener(this);
 btn9.setOnClickListener(this);
 btnClear.setOnClickListener(this);
 btnPlus.setOnClickListener(this);
 btnSubtract.setOnClickListener(this);
 btnMultiply.setOnClickListener(this);
 btnDivide.setOnClickListener(this);
 btnPoint.setOnClickListener(this);
 btnSum.setOnClickListener(new click());
 //给所有按钮注册点击事件
 }
 
 @Override
 public void onClick(View v) {
 String input=text.getText().toString();
 switch (v.getId()){
 case R.id.btn0:
 case R.id.btn1:
 case R.id.btn2:
 case R.id.btn3:
 case R.id.btn4:
 case R.id.btn5:
 case R.id.btn6:
 case R.id.btn7:
 case R.id.btn8:
 case R.id.btn9:
 case R.id.btnPoint:
 
 text.setText(input ((Button)v).getText());
 break;
 
 case R.id.btnPlus:
 case R.id.btnSubtract:
 case R.id.btnMultiply:
 case R.id.btnDivide:
 
 text.setText(input   " "   ((Button)v).getText()   " "); //给运算符前后加空格，好判断
 break;
 
 case R.id.btnClear:
 text.setText("");
 break;
 }
 }
 class click implements View.OnClickListener {
 public void onClick (View v) {
 getResult();
 }
 }
 
 private void getResult () {
 String str1 = text.getText().toString();
 if(str1 == null || str1.equals("")){
 return;
 }
 if(!str1.contains(" ")){
 return ;
 }
 
 double result = 0;
// 第一个数的字符串
 String s1 = str1.substring(0,str1.indexOf(" "));
// 运算符
 String op = str1.substring(str1.indexOf(" ") 1,str1.indexOf(" ") 2);
// 第二个数的字符串
 String s2 = str1.substring(str1.indexOf(" ") 3);
 
 double d1 = Double.parseDouble(s1);//将数字字符串转为double类型
 double d2 = Double.parseDouble(s2);
 if (op.equals(" ")) { //加法运算
 result = d1   d2;
 } else if (op.equals("-")) { //减法运算
 result = d1 - d2;
 } else if (op.equals("*")) { //乘法运算
 result = d1 * d2;
 } else if (op.equals("/")) { //除法运算
 if (d2 == 0) { //如果被除数是0
 result = 0; //则结果是0
 }
 else {
 result = d1 / d2;
 }
 }
 
 text.setText(str1   " = "   result); //显示计算结果
 
 if (!s1.contains(".") && !s2.contains(".") && !op.equals("/")) {//如果两个整数且不是出发运算
 int r = (int) result; //则结果转为整数
 text.setText(str1   " = "   r );
 }
 
 }
 
}