在 Java 中显示 Android 计算器的最后一个运算符

Question

我正在为 Java 中的 Android 编写一个计算器，在我的程序完成之前还有最后一件事要做。

比如我按这个顺序：5,+,-,/,*,5，运算结果就是“5*5”。实际上，当我这样做时，它只保留第一个操作员。我该如何解决？我无法完成它，它让我发疯。如果有人能帮助我，我将不胜感激。

这是我的代码，我希望它很干净并且你能理解它：

    package com.example.calcapp_training;

    import androidx.appcompat.app.AppCompatActivity;
    import android.os.Bundle;
    import android.view.View;
    import android.widget.Button;
    import android.widget.ImageView;
    import android.widget.TextView;

    public class MainActivity extends AppCompatActivity {
        Button btnMinus, btnDiv, btnMult, btnPlus, btnDel, btnEqual, btnPoint, btn0, btn1, btn2, btn3, btn4, btn5, btn6, btn7, btn8, btn9;
        TextView input, result;
        TextView error;
        ImageView image;
        double mValueOne, mValueTwo;
        int Calculation;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final TextView errorMessage = findViewById(R.id.error);
        final TextView welcomeMessage = findViewById(R.id.welcome);

        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);
        btnPlus = (Button) findViewById(R.id.btnPlus );
        btnMinus = (Button) findViewById(R.id.btnMinus );
        btnMult = (Button) findViewById(R.id.btnMult );
        btnDiv = (Button) findViewById(R.id.btnDiv );
        btnDel = (Button) findViewById(R.id.btnDel);
        btnEqual = (Button) findViewById(R.id.btnEqual);
        btnPoint = (Button) findViewById(R.id.btnPoint);
        input = (TextView) findViewById(R.id.input);
        result = (TextView) findViewById(R.id.result);
        error = (TextView) findViewById(R.id.error);
        image = (ImageView) findViewById(R.id.image);

        btn1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                welcomeMessage.setVisibility(View.INVISIBLE);
                result.setText(result.getText() + "1");

            }
        });

        btn2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                welcomeMessage.setVisibility(View.INVISIBLE);
                result.setText(result.getText() + "2");

            }
        });

        btn3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                welcomeMessage.setVisibility(View.INVISIBLE);
                result.setText(result.getText() + "3");

            }
        });

        btn4.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                welcomeMessage.setVisibility(View.INVISIBLE);
                result.setText(result.getText() + "4");

            }
        });

        btn5.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                welcomeMessage.setVisibility(View.INVISIBLE);
                result.setText(result.getText() + "5");

            }
        });

        btn6.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                welcomeMessage.setVisibility(View.INVISIBLE);
                result.setText(result.getText() + "6");

            }
        });

        btn7.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                welcomeMessage.setVisibility(View.INVISIBLE);
                result.setText(result.getText() + "7");

            }
        });

        btn8.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                welcomeMessage.setVisibility(View.INVISIBLE);
                result.setText(result.getText() + "8");

            }
        });

        btn9.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                welcomeMessage.setVisibility(View.INVISIBLE);
                result.setText(result.getText() + "9");

            }
        });

        btn0.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                welcomeMessage.setVisibility(View.INVISIBLE);
                result.setText(result.getText() + "0");

            }
        });

        btnDel.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                welcomeMessage.setVisibility(View.INVISIBLE);
                result.setText("");
                input.setText("");

            }
        });

        btnPoint.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                welcomeMessage.setVisibility(View.INVISIBLE);
                result.setText(result.getText() + ".");

            }
        });

        btnPlus.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                if( result.getText().toString().equals("") != true ) {

                    mValueOne=Double.parseDouble(result.getText()+"");
                    Calculation = 1;
                    result.setText(null);

                }
            }
        });

        btnMinus.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                if( result.getText().toString().equals("") != true ) {

                    mValueOne=Double.parseDouble(result.getText()+"");
                    Calculation = 2;
                    result.setText(null);

                }
            }
        });

        btnMult.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                if( result.getText().toString().equals("") != true ) {

                    mValueOne=Double.parseDouble(result.getText()+"");
                    Calculation = 3;
                    result.setText(null);

                }
            }
        });

        btnDiv.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                if( result.getText().toString().equals("") != true ) {

                    mValueOne=Double.parseDouble(result.getText()+"");
                    Calculation = 4;
                    result.setText(null);

                }
            }
        });

        btnEqual.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                mValueTwo = Double.parseDouble(result.getText() + "");
                if (Calculation == 1) {

                    result.setText(mValueOne + mValueTwo + "");
                    Calculation = 1;

                }

                else if (Calculation == 2) {

                    result.setText(mValueOne - mValueTwo + "");
                    Calculation = 2;

                }

                else if (Calculation == 3) {

                    result.setText(mValueOne * mValueTwo + "");
                    Calculation = 3;

                }

                else if (Calculation == 4) {

                    double a = Math.round(mValueOne / mValueTwo);
                    result.setText(a + "" );

                    if(mValueTwo == 0) {

                        errorMessage.setVisibility(View.VISIBLE);
                        result.setText(mValueOne / mValueTwo + "");
                        Calculation = 4;

                    } else {

                        errorMessage.setVisibility(View.INVISIBLE);

                    }

                    Calculation = 4;

                }
            }
        });
    }
}

Answer 1

把所有的操作按钮都点击Calculation这样的外部条件：

btnPlus.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {

        if( result.getText().toString().equals("") != true ) {

            mValueOne=Double.parseDouble(result.getText()+"");

            result.setText(null);

        }
       Calculation = 1;
    }
});

在 Java 中显示 Android 计算器的最后一个运算符

Display the last operator for an Android calculator in Java

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