用Android Studio开发第一个APP——一元二次方程求解器

开发工具

Android Studio

开发过程

1.使用Android Studio新建一个空项目。

2.创建布局

长下面这样（不太好看😁）

布局.png

布局代码

 spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="assembly" cid="n27" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: &quot;Fira Code&quot;, Consolas, &quot;Lucida Console&quot;, Courier, monospace, &quot;Helvetica Neue&quot;, Helvetica, &quot;Arial sans-serif&quot;; font-size: 0.9rem; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(40, 44, 52); position: relative !important; padding: 6px 10px; box-shadow: rgba(0, 0, 0, 0.16) 0px 2px 5px 0px, rgba(0, 0, 0, 0.12) 0px 2px 10px 0px; margin-bottom: 2.10526rem; border: none; border-radius: 6px; width: inherit; color: rgb(40, 44, 52); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;"><?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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:paddingLeft="16dp"
 android:paddingRight="16dp" >
 <TextView
 android:id="@+id/tv_equation"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_centerHorizontal="true"
 android:textAlignment="center"
 android:layout_marginTop="20dp"
 android:text="@string/equation"
 android:textColor="#000"
 android:textSize="40sp" />

 <LinearLayout
 android:id="@+id/linearlayout1"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_centerVertical="true"
 android:layout_below="@+id/tv_equation"
 android:layout_marginLeft="10dp"
 android:layout_marginTop="15dp"
 android:layout_marginRight="10dp"
 android:layout_marginBottom="10dp"
 android:background="#ffffff">
 <TextView
 android:id="@+id/tv_a"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:padding="10dp"
 android:text="a:"
 android:layout_marginBottom="1dp"
 android:layout_marginTop="1dp"
 android:textColor="#000"
 android:textSize="40sp"/>
 <EditText
 android:id="@+id/ev_a"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:hint="请输入参数a的值"
 android:inputType="numberSigned"
 android:background="@null"
 android:padding="10dp"
 android:textSize="25sp"/>
 </LinearLayout>

 <LinearLayout
 android:id="@+id/linearlayout2"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_centerVertical="true"
 android:layout_below="@+id/linearlayout1"
 android:layout_marginLeft="10dp"
 android:layout_marginTop="1dp"
 android:layout_marginRight="10dp"
 android:layout_marginBottom="10dp"
 android:background="#ffffff">
 <TextView
 android:id="@+id/tv_b"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:padding="10dp"
 android:text="b:"
 android:layout_marginBottom="1dp"
 android:layout_marginTop="1dp"
 android:textColor="#000"
 android:textSize="40sp"/>
 <EditText
 android:id="@+id/ev_b"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:hint="请输入参数b的值"
 android:inputType="numberSigned"
 android:background="@null"
 android:padding="10dp"
 android:textSize="25sp"/>
 </LinearLayout>

 <LinearLayout
 android:id="@+id/linearlayout3"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_centerVertical="true"
 android:layout_below="@+id/linearlayout2"
 android:layout_marginLeft="10dp"
 android:layout_marginTop="1dp"
 android:layout_marginRight="10dp"
 android:layout_marginBottom="10dp"
 android:background="#ffffff">
 <TextView
 android:id="@+id/tv_c"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:padding="10dp"
 android:text="c:"
 android:layout_marginTop="1dp"
 android:textColor="#000"
 android:textSize="40sp"/>
 <EditText
 android:id="@+id/ev_c"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:hint="请输入参数c的值"
 android:inputType="numberSigned"
 android:background="@null"
 android:padding="10dp"
 android:textSize="25sp"/>
 </LinearLayout>


 <LinearLayout
 android:id="@+id/linearlayout4"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_centerVertical="true"
 android:layout_below="@+id/linearlayout3"
 android:layout_marginLeft="10dp"
 android:layout_marginTop="1dp"
 android:layout_marginRight="10dp"
 android:layout_marginBottom="10dp"
 android:background="#ffffff">
 <TextView
 android:id="@+id/tv_answer"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:padding="10dp"
 android:text="答案:"
 android:textColor="#000"
 android:textSize="25sp"/>
 <TextView
 android:id="@+id/ev_answer"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:background="@null"
 android:padding="10dp"
 android:textSize="25sp"/>
 </LinearLayout>

 <LinearLayout
 android:id="@+id/linearlayout5"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_centerVertical="true"
 android:layout_below="@+id/linearlayout4"
 android:layout_marginLeft="10dp"
 android:layout_marginTop="1dp"
 android:layout_marginRight="10dp"
 android:layout_marginBottom="10dp"
 android:background="#ffffff">

 <Button
 android:id="@+id/btn_clear"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:layout_centerHorizontal="true"
 android:text="Clear"
 android:textSize="35dp"
 android:layout_marginTop="10dp"
 tools:ignore="InvalidId"
 android:layout_weight="1"/>

 <Button
 android:id="@+id/btn1"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:layout_centerHorizontal="true"
 android:text="求解"
 android:textSize="40dp"
 android:layout_marginLeft="30dp"
 android:layout_marginTop="10dp"
 tools:ignore="InvalidId"
 android:layout_weight="1"/>
 </LinearLayout>

</RelativeLayout>

3.Java代码的编写

MainActivity.java 代码：

 mdtype="fences" cid="n38" lang="java" class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" style="box-sizing: border-box; overflow: visible; font-family: &quot;Fira Code&quot;, Consolas, &quot;Lucida Console&quot;, Courier, monospace, &quot;Helvetica Neue&quot;, Helvetica, &quot;Arial sans-serif&quot;; font-size: 0.9rem; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(40, 44, 52); position: relative !important; padding: 6px 10px; box-shadow: rgba(0, 0, 0, 0.16) 0px 2px 5px 0px, rgba(0, 0, 0, 0.12) 0px 2px 10px 0px; margin-bottom: 2.10526rem; border: none; border-radius: 6px; width: inherit; color: rgb(40, 44, 52); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">package com.example.calculator;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import com.example.calculator.utils.CalculateUtils;

public class MainActivity extends AppCompatActivity {

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

 EditText aValue=(EditText)findViewById(R.id.ev_a);
 EditText bValue=(EditText)findViewById(R.id.ev_b);
 EditText cValue=(EditText)findViewById(R.id.ev_c);
 TextView answer_view=(TextView)findViewById(R.id.ev_answer);
 Button btn1=(Button)findViewById(R.id.btn1);
 Button btn_clear=(Button)findViewById(R.id.btn_clear);

 //点击求解
 btn1.setOnClickListener(new View.OnClickListener() {
 @Override
 public void onClick(View v) {
 CalculateUtils.calculate(aValue, bValue, cValue, answer_view);
 }
 });

 //点击Clear
 btn_clear.setOnClickListener(new View.OnClickListener() {
 @Override
 public void onClick(View v) {
 aValue.setText("");
 bValue.setText("");
 cValue.setText("");
 answer_view.setText("");
 }
 });

 }
}

CalculateUtils.java 代码：

<pre mdtype="fences" cid="n51" lang="java" class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" style="box-sizing: border-box; overflow: visible; font-family: &quot;Fira Code&quot;, Consolas, &quot;Lucida Console&quot;, Courier, monospace, &quot;Helvetica Neue&quot;, Helvetica, &quot;Arial sans-serif&quot;; font-size: 0.9rem; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(40, 44, 52); position: relative !important; padding: 6px 10px; box-shadow: rgba(0, 0, 0, 0.16) 0px 2px 5px 0px, rgba(0, 0, 0, 0.12) 0px 2px 10px 0px; margin-bottom: 2.10526rem; border: none; border-radius: 6px; width: inherit; color: rgb(40, 44, 52); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">package com.example.calculator.utils;

import android.util.Log;
import android.widget.EditText;
import android.widget.TextView;

public class CalculateUtils {
 private static final String TAG = "KING";
 public static void calculate(EditText aValue, EditText bValue, EditText cValue, TextView answer_view) {
 double a, b, c;
 a = b = c = 0;
 if(aValue.getText().length() > 0)
 a=Double.parseDouble(aValue.getText().toString());
 if(bValue.getText().length() > 0)
 b=Double.parseDouble(bValue.getText().toString());
 if(cValue.getText().length() > 0)
 c=Double.parseDouble(cValue.getText().toString());

 if(a == 0){
 if (b != 0){
 answer_view.setText("x="+(-c/b));
 } else answer_view.setText("嘿嘿，爷不会\uD83E\uDD23\uD83E\uDD23");
 } else {
 double x1, x2;
 double delta = b * b - 4 * a * c;
 if (delta < 0) {
 answer_view.setText("该方程无实数根");
 } else if (delta == 0) {
 x1 = (-b) / (2 * a);
 answer_view.setText("该方程有一个实数根：x=" + x1);
 } else {
 x1 = ((-b + Math.sqrt(delta)) / (2 * a));
 x2 = ((-b - Math.sqrt(delta)) / (2 * a));
 answer_view.setText("该方程有两个实数根：x1=" + x1 + "\t\t" + "x2=" + x2);
 }
 }
 }
}

4.给APP换一个图标

找一张图片，放进资源文件夹。

配置 AndroidManifest.xml 文件，在 android:icon 后添加图片名称。

android:icon="@mipmap/calculator_icon"

成果

做完后大概就是这样的

图标：
图标.jpg

APP界面：
界面.jpg
最后编辑于 ：
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