[英]Decimal points in calculator android
I am creating a calculator app in android.我正在 android 中创建一个计算器应用程序。 The issue is how can I check for existence of two decimals in a single numeric value .
问题是如何检查单个数值中是否存在两位小数。 Currently my calculator allows inputs such as
1.2.3
which is illegal .目前我的计算器允许输入如
1.2.3
这是非法的。 It must allow a decimal if an operator has been used.如果使用了运算符,则必须允许使用小数。 Eg
1.1+2.2
is legal but 1.1.1+2.2
isn't.例如
1.1+2.2
是合法的,但1.1.1+2.2
不是。 Here is my code for decimal handling:这是我的十进制处理代码:
public class TrialCalculator extends AppCompatActivity implements Button.OnClickListener {
Button btn1, btn2, btnBack, btn3, btn4, btn5, btn6, btn7, btn8, btn9, btn0, btnPlus, btnMinus, btnMul, btnDiv, btnEquals, btnClear, btnDecimal, btnPercent;
EditText calcResult;
double number = 0;
private char opcode = '1';
private void handleDecimal() {
if (opcode == 0) clear();
if (calcResult.getText() == null) {
calcResult.setText("0.");
calcResult.setSelection(2);
} else {
String txt = calcResult.getText().toString();
if (txt.lastIndexOf(".")<txt.length()-1) {
calcResult.append(".");
}
}
}
}
I am calling the buttonDot
from onClick
Method.我从
onClick
方法调用buttonDot
。
One solution is to have a flag which keeps track of the decimal:一种解决方案是拥有一个跟踪小数的标志:
class MyCalculator {
private hasDecimal = false;
// ...
}
Set this flag to true
the first time that the user types a decimal.用户第一次键入小数时,将此标志设置为
true
。 Then check the flag to see if a decimal has been previously typed.然后检查标志以查看之前是否输入了小数。
Of course, this only works if you are responding to each key press directly rather than getting the entire input from a EditText
after the user has typed the entire number.当然,这仅适用于直接响应每个按键而不是在用户输入整个数字后从
EditText
获取整个输入的情况。
You can use regex with matches
function您可以将正则表达式与
matches
功能一起使用
\\\\d*
mean match zero or more digits \\\\d*
表示匹配零个或多个数字
(\\\\.\\\\d+)?
match a .
匹配一个
.
followed by one or more digits , ?
后跟一位或多位数字 ,
?
mean matches between zero or one times of given group给定组的零次或一次之间的平均匹配
Regex Demo : note with matches
function in java, we don't need ^
start and $
ending anchors正则表达式演示:注意 java 中的
matches
功能,我们不需要^
开始和$
结束锚点
Code代码
if (txt.matches("\\d*(\\.\\d+)?")) {
// number has one decimal
}
else{
// number has more than one decimal
}
Note: if you don't want to allow values like .5
then use \\\\d+
instead of \\\\d*
as注意:如果你不想允许像
.5
这样的值,那么使用\\\\d+
而不是\\\\d*
作为
\\\\d+(\\\\.\\\\d+)?
As suggested by @Code-Apprentice , if you want to accept values like 4343.
etc you can use正如@Code-Apprentice 所建议的,如果你想接受像
4343.
这样的值,你可以使用
\\d*(\\.\\d*)?
Using text watcher使用文本观察器
calcResult.addTextChangedListener(new TextWatcher() {
@Override
public void onTextChanged(CharSequence s, int start, int before, int count) {}
@Override
public void beforeTextChanged(CharSequence s, int start, int count, int after) {}
@Override
public void afterTextChanged(Editable s) {
boolean flag = s.toString().matches("\\d*(\\.\\d*)?");
if(!flag){
// calcResult.setError...
// you display a toast
}
}
});
Update : To match multiple values with operators , you can use更新:要将多个值与运算符匹配,您可以使用
(\\d*(\\.\\d*)?([+\\-*%\\]|$))*
Test Cases测试用例
String pat="(\\d*(\\.\\d*)?([+\\-*%\\]|$))*";
System.out.println("4.5-3.3+3.4".matches(pat));
System.out.println(".5".matches(pat));
System.out.println("4".matches(pat));
System.out.println("4.5.5-4.4".matches(pat));
System.out.println("4.44.5+4.4.4".matches(pat));
System.out.println("4.".matches(pat));
Output :输出 :
true
true
true
false
false
true
lastIndexOf
returns -1 if the character is not found in the string.如果在字符串中找不到该字符,则
lastIndexOf
返回 -1。 So your condition txt.lastIndexOf(".")<txt.length()-1
is always true
.所以你的条件
txt.lastIndexOf(".")<txt.length()-1
总是true
。 You could change it to你可以把它改成
txt.lastIndexOf(".") == -1
To check for existence of two decimals in a single no then split the string by decimal.要检查单个 no 中是否存在两个小数,然后按十进制拆分字符串。
for eg,例如,
String txt = calcResult.getText().toString();
String[] decimals = txt.split("\\.");
if(decimals.length > 2) {
// txt contains more than 1 decimal.
// Your logic ..
}
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