先上图：
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:orientation="vertical"
android:layout_height="match_parent"
android:weightSum="1">
<TextView
android:id="@+id/textView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="TextView"
/>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">
<Button
android:id="@+id/button4"
android:layout_width="193dp"
android:layout_height="wrap_content"
android:text="显示" />
<Button
android:id="@+id/button3"
android:layout_width="187dp"
android:layout_height="wrap_content"
android:text="下一题"
android:layout_weight="0.01" />
</LinearLayout>
</LinearLayout>
看到上面的图，大家肯定会说，这不算错了么，其实这是四舍五入的结果，
代码逻辑，为：
- random生成随机数，包括数字a,b,c
- 加减乘除的实现：以switch列出所有的加减乘除的组合，三位数的算数（包括2位数）总共20种，列出所有可能。
- 显示答案：在同一个random下，例如显示a+b+c=?，然后在另一个方法中显示a+b+c=d。在点击下一题时，再次生成随机数，以此类推。
代码如下：
package com.example.myapplication;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import java.util.Random;
public class MainActivity extends AppCompatActivity {
private int a, b, c, ysf;
private TextView tv;
private Button show, next;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tv = (TextView) findViewById(R.id.tv);
show = (Button) findViewById(R.id.show);
next = (Button) findViewById(R.id.next);
rd();
show.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
answer(ysf,a,b,c);
}
});
next.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
rd();
show(ysf,a,b,c);
}
});
}
private void answer(int ty,int a,int b,int c){
switch (ty) {
//将所有的可能全列出来
//两个数的算法
case 0:
tv.setText(a+"+"+b+"="+(a+b));
break;
case 1:
tv.setText(a+"-"+b+"="+(a-b));
break;
case 2:
tv.setText(a+"*"+b+"="+(a*b));
break;
case 3:
tv.setText(a+"/"+b+"="+(a/b));
break;
//三个数的四则运算，共16种
case 4:
tv.setText(a + "+" + b + "-" + c + "=" + (a + b - c));
break;
case 5:
tv.setText(a + "+" + b + "+" + c + "=" + (a + b + c));
break;
case 6:
tv.setText(a + "+" + b + "*" + c + "=" + (a + b * c));
break;
case 7:
tv.setText(a + "+" + b + "/" + c + "=" + (a + b / c));
break;
case 8:
tv.setText(a+"-"+b+"-"+c+"="+(a-b-c));
break;
case 9:
tv.setText(a+"-"+b+"+"+c+"="+(a-b+c));
break;
case 10:
tv.setText(a+"-"+b+"*"+c+"="+(a-b*c));
break;
case 11:
tv.setText(a+"-"+b+"/"+c+"="+(a-b/c));
break;
case 12:
tv.setText(a+"*"+b+"*"+c+"="+(a*b*c));
break;
case 13:
tv.setText(a+"*"+b+"+"+c+"="+(a*b+c));
break;
case 14:
tv.setText(a+"*"+b+"-"+c+"="+(a*b-c));
break;
case 15:
tv.setText(a+"*"+b+"/"+c+"="+(a*b/c));
break;
case 16:
tv.setText(a+"/"+b+"/"+c+"="+(a/b/c));
break;
case 17:
tv.setText(a+"/"+b+"+"+c+"="+(a/b+c));
break;
case 18:
tv.setText(a+"/"+b+"-"+c+"="+(a/b-c));
break;
case 19:
tv.setText(a+"/"+b+"*"+c+"="+(a/b*c));
}
}
private void show(int ty,int a,int b,int c){
switch (ty) {
//将所有的可能全列出来
//两个数的算法
case 0:
tv.setText(a+"+"+b+"="+"?");
break;
case 1:
tv.setText(a+"-"+b+"="+"?");
break;
case 2:
tv.setText(a+"*"+b+"="+"?");
break;
case 3:
tv.setText(a+"/"+b+"="+"?");
break;
//三个数的四则运算，共16种
case 4:
tv.setText(a + "+" + b + "-" + c + "=" + "?");
break;
case 5:
tv.setText(a + "+" + b + "+" + c + "=" + "?");
break;
case 6:
tv.setText(a + "+" + b + "*" + c + "=" + "?");
break;
case 7:
tv.setText(a + "+" + b + "/" + c + "=" + "?");
break;
case 8:
tv.setText(a+"-"+b+"-"+c+"="+"?");
break;
case 9:
tv.setText(a+"-"+b+"+"+c+"="+"?");
break;
case 10:
tv.setText(a+"-"+b+"*"+c+"="+"?");
break;
case 11:
tv.setText(a+"-"+b+"/"+c+"="+"?");
break;
case 12:
tv.setText(a+"*"+b+"*"+c+"="+"?");
break;
case 13:
tv.setText(a+"*"+b+"+"+c+"="+"?");
break;
case 14:
tv.setText(a+"*"+b+"-"+c+"="+"?");
break;
case 15:
tv.setText(a+"*"+b+"/"+c+"="+"?");
break;
case 16:
tv.setText(a+"/"+b+"/"+c+"="+"?");
break;
case 17:
tv.setText(a+"/"+b+"+"+c+"="+"?");
break;
case 18:
tv.setText(a+"/"+b+"-"+c+"="+"?");
break;
case 19:
tv.setText(a+"/"+b+"*"+c+"="+"?");
}
}
private void rd() {
Random random = new Random();
random.nextInt();
a = random.nextInt(100);
b = random.nextInt(100);
c = random.nextInt(100);
ysf = random.nextInt(19);
}
}