源代码下载：https://gitee.com/zha-yingying/calculator.git

1.建立一个新的Layout，我这里使用的是GridLayout（网格布局），提取屏幕宽度（方便后面设置子控件的宽度）GridLayout的特点是自定义网格布局有几行几列，我们可以将自控件自定义放在第几行第几列。

2.建立一个新的textview（文本框）作为我们计算器输入数字运算符号的界面，将textview放在第一行第一列，设置宽度为屏幕的宽度，这边我们需要提取一下屏幕的宽度。

3.添加子控件 添加按钮到布局上（数字+运算符号+等于符号）分别设置它们的位置，我这里的GridLayout设置的是八行四列，宽度为屏幕宽度的四分之一。

4.给每个控件都加上点击事件，给按钮设置监听器。在MainaActivity中使用enum（枚举）方法，分为四种情况（1）无按钮操作（2）上一次按钮为数字（3）上一次按钮为运算符号（4）上一次按钮为等于，分别写出其操作内容，需要在点击事件中添加状态。

提取屏幕宽度：

WindowManager wm = (WindowManager) this.getSystemService(this.WINDOW_SERVICE);

int width = wm.getDefaultDisplay().getWidth();

添加按钮：

（1）添加数字按钮（依次添加0-9和"."按钮）

Button button1 = new Button(this);
layout1.addView(button1);
GridLayout.LayoutParams bt1 = (GridLayout.LayoutParams) button1.getLayoutParams();
bt1.rowSpec = GridLayout.spec(6,1,GridLayout.CENTER,1);
bt1.columnSpec = GridLayout.spec(0,1,GridLayout.CENTER,1);
bt1.width = width/4;
button1.setText("1");
button1.setLayoutParams(bt1);

（2）添加运算符号按钮（加减乘除这一类）

减号为例：

Button buttonminus = new Button(this);
layout1.addView(buttonminus);
buttonminus.setText("-");
GridLayout.LayoutParams btjian = (GridLayout.LayoutParams) buttonminus.getLayoutParams();
btjian.rowSpec = GridLayout.spec(6, 1, GridLayout.CENTER, 1);
btjian.columnSpec = GridLayout.spec(3, 1, GridLayout.CENTER, 1);
btjian.width = width / 4;
buttonminus.setLayoutParams(btjian);

（3）添加等号按钮

Button buttonequal = new Button(this);
layout1.addView(buttonequal);
buttonequal.setText("=");
GridLayout.LayoutParams btdy = (GridLayout.LayoutParams) buttonequal.getLayoutParams();
btdy.rowSpec = GridLayout.spec(7, 1, GridLayout.CENTER, 1);
btdy.columnSpec = GridLayout.spec(3, 1, GridLayout.CENTER, 1);
btdy.width = width / 4;
buttonequal.setLayoutParams(btdy);

给按钮添加点击事件，设置状态：

（1）数字按钮

button1.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        NumberClick("1");
         
    }
});

（2）运算符号按钮（减号为例子）

buttonminus.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        OperationClick("-");
        operationType = OperationType.Minus;
    }
});

（3）等号按钮

buttonequal.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            EqualClick("=");
        }
    });
}

枚举法举例

新建两个enum的类

ClickType判断上一次按钮是数字/运算符号/等于符号

public enum ClickType {
    None,
    Number,
    Operation,
    Equqal,
}

OperationType判断上一次的运算符号是加/减/乘/除

public enum OperationType {
    None,
    Plus,
    Minus,
    Multiply,
    Divide,

}

在MainActivity里：

private ClickType clickType = ClickType.None;

private OperationType operationType = OperationType.None;

//按下数字键时

private void NumberClick(String n){
    switch (clickType){
        case None:
            textView.setText(n);
            break;
        case Number:
            String an = textView.getText().toString();
            textView.setText(an+n);
            break;
        case Operation:
            textView.setText(n);
            break;
        case Equqal:
            textView.setText(n);
            break;
    }
    clickType = ClickType.Number;
}

//按下操作符号时

private  void OperationClick(String n1){
    switch ((clickType)){
        case None:
            textView.setText("mistake");
            break;

            case Number:
          

switch ((operationType)){

        case None:
            String an2 = textView.getText().toString();
            a = Double.valueOf(an2);
            textView.setText(an2+n1);
            break;

        case Plus:
            String an3 = textView.getText().toString();
            b = Double.valueOf(an3);
            a = a + b;
            textView.setText(an3+n1);
            textView.setText(""+a);
            break;

 case Minus:
                String an4 = textView.getText().toString();
                b = Double.valueOf(an4);
                a = a - b;
                textView.setText(an4+"-");
                textView.setText(""+a);
                break;

            case Divide:
                String an5 = textView.getText().toString();
                b = Double.valueOf(an5);
                a = a / b;
                textView.setText(an5+n1);
                textView.setText(""+a);
                break;

            case Multiply:
                String an6 = textView.getText().toString();
                b = Double.valueOf(an6);
                a = a * b;
                textView.setText(an6+n1);
                textView.setText(""+a);
                break;
        }
        break;
case  Operation:
    textView.setText("mistake");
    break;

case Equqal:
            String an1 = textView.getText().toString();
            a = Double.valueOf(an1);
            break;
    }
    clickType = ClickType.Operation;
}

//按下等于号时

private void EqualClick(String n2){
    switch ((clickType)){
        case None:
            textView.setText("mistake");
            break;
        case Number:

            switch ((operationType)){
                case None:
                    textView.setText(""+a);

                case Plus:
                    String bn = textView.getText().toString();
                    b = Double.valueOf(bn);
                    b = a + b;
                    textView.setText(""+b);
                    a = 0;
                    break;

 case  Minus:
                        String bn1 = textView.getText().toString();
                        b = Double.valueOf(bn1);
                        b = a - b;
                        textView.setText(""+b);
                        a = 0;
                        break;

                    case Multiply:
                        String bn2 = textView.getText().toString();
                        b = Double.valueOf(bn2);
                        b = a * b;
                        textView.setText(""+b);
                        a = 0;
                        break;

                    case Divide:
                        String bn3 = textView.getText().toString();
                        b = Double.valueOf(bn3);
                        b = a / b;
                        textView.setText(""+b);
                        a = 0;
                        break;
                }
                break;
            case Operation:
                textView.setText("mistake");
                break;
            case Equqal:
                textView.setText("mistake");
                break;
        }
        clickType = ClickType.Equqal;
    }