计算器的Android代码中的互惠

Question

这是我正在制作的Android计算器应用的代码：

package com.example.calculator;

import java.text.DecimalFormat;
import java.text.NumberFormat;
import java.util.Iterator;
import java.util.Stack;

import android.app.Activity;
import android.os.Bundle;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.TextView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.GridView;
import android.view.View;
import android.view.View.OnClickListener;

public class main extends Activity {
    GridView mKeypadGrid;
    TextView userInputText;
    TextView memoryStatText;

    Stack<String> mInputStack;
    Stack<String> mOperationStack;

    KeypadAdapter mKeypadAdapter;
    TextView mStackText;
    boolean resetInput = false;
    boolean hasFinalResult = false;

    String mDecimalSeperator;
    double memoryValue = Double.NaN;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        DecimalFormat currencyFormatter = (DecimalFormat) NumberFormat
                .getInstance();
        char decimalSeperator = currencyFormatter.getDecimalFormatSymbols()
                .getDecimalSeparator();
        mDecimalSeperator = Character.toString(decimalSeperator);

        setContentView(R.layout.main);

        // Create the stack
        mInputStack = new Stack<String>();
        mOperationStack = new Stack<String>();

        // Get reference to the keypad button GridView
        mKeypadGrid = (GridView) findViewById(R.id.grdButtons);

        // Get reference to the user input TextView
        userInputText = (TextView) findViewById(R.id.txtInput);
        userInputText.setText("0");

        memoryStatText = (TextView) findViewById(R.id.txtMemory);
        memoryStatText.setText("");

        mStackText = (TextView) findViewById(R.id.txtStack);

        // Create Keypad Adapter
        mKeypadAdapter = new KeypadAdapter(this);

        // Set adapter of the keypad grid
        mKeypadGrid.setAdapter(mKeypadAdapter);

        // Set button click listener of the keypad adapter
        mKeypadAdapter.setOnButtonClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                Button btn = (Button) v;
                // Get the KeypadButton value which is used to identify the
                // keypad button from the Button's tag
                KeypadButton keypadButton = (KeypadButton) btn.getTag();

                // Process keypad button
                ProcessKeypadInput(keypadButton);
            }
        });

        mKeypadGrid.setOnItemClickListener(new OnItemClickListener() {
            public void onItemClick(AdapterView<?> parent, View v,
                    int position, long id) {

            }
        });

    }

    private void ProcessKeypadInput(KeypadButton keypadButton) {
        //Toast.makeText(this, keypadButton.getText(), Toast.LENGTH_SHORT).show();
        String text = keypadButton.getText().toString();
        String currentInput = userInputText.getText().toString();

        int currentInputLen = currentInput.length();
        String evalResult = null;
        double userInputValue = Double.NaN;

        switch (keypadButton) {
        case BACKSPACE: // Handle backspace
            // If has operand skip backspace
            if (resetInput)
                return;

            int endIndex = currentInputLen - 1;

            // There is one character at input so reset input to 0
            if (endIndex < 1) {
                userInputText.setText("0");
            }
            // Trim last character of the input text
            else {
                userInputText.setText(currentInput.subSequence(0, endIndex));
            }
            break;
        case SIGN: // Handle -/+ sign
            // input has text and is different than initial value 0
            if (currentInputLen > 0 && currentInput != "0") {
                // Already has (-) sign. Remove that sign
                if (currentInput.charAt(0) == '-') {
                    userInputText.setText(currentInput.subSequence(1,
                            currentInputLen));
                }
                // Prepend (-) sign
                else {
                    userInputText.setText("-" + currentInput.toString());
                }
            }
            break;
        case CE: // Handle clear input
            userInputText.setText("0");
            break;
        case INVERT:
            if (currentInput != "0") {
                userInputText.setText("1/" + currentInput);
            }
            break;
        case C: // Handle clear input and stack
            userInputText.setText("0");
            clearStacks();
            break;
        case DECIMAL_SEP: // Handle decimal separator
            if (hasFinalResult || resetInput) {
                userInputText.setText("0" + mDecimalSeperator);
                hasFinalResult = false;
                resetInput = false;
            } else if (currentInput.contains("."))
                return;
            else
                userInputText.append(mDecimalSeperator);
            break;
        case DIV:
        case PLUS:
        case MINUS:
        case MULTIPLY:
            if (resetInput) {
                mInputStack.pop();
                mOperationStack.pop();
            } else {
                if (currentInput.charAt(0) == '-') {
                    mInputStack.add("(" + currentInput + ")");
                } else {
                    mInputStack.add(currentInput);
                }
                mOperationStack.add(currentInput);
            }

            mInputStack.add(text);
            mOperationStack.add(text);

            dumpInputStack();
            evalResult = evaluateResult(false);
            if (evalResult != null)
                userInputText.setText(evalResult);

            resetInput = true;
            break;
        case CALCULATE:
            if (mOperationStack.size() == 0)
                break;

            mOperationStack.add(currentInput);
            evalResult = evaluateResult(true);
            if (evalResult != null) {
                clearStacks();
                userInputText.setText(evalResult);
                resetInput = false;
                hasFinalResult = true;
            }
            break;
        case M_ADD: // Add user input value to memory buffer
            userInputValue = tryParseUserInput();
            if (Double.isNaN(userInputValue))
                return;
            if (Double.isNaN(memoryValue))
                memoryValue = 0;
            memoryValue += userInputValue;
            displayMemoryStat();

            hasFinalResult = true;

            break;
        case M_REMOVE: // Subtract user input value to memory buffer
            userInputValue = tryParseUserInput();
            if (Double.isNaN(userInputValue))
                return;
            if (Double.isNaN(memoryValue))
                memoryValue = 0;
            memoryValue -= userInputValue;
            displayMemoryStat();
            hasFinalResult = true;
            break;
        case MC: // Reset memory buffer to 0
            memoryValue = Double.NaN;
            displayMemoryStat();
            break;
        case MR: // Read memoryBuffer value
            if (Double.isNaN(memoryValue))
                return;
            userInputText.setText(doubleToString(memoryValue));
            displayMemoryStat();
            break;
        case MS: // Set memoryBuffer value to user input
            userInputValue = tryParseUserInput();
            if (Double.isNaN(userInputValue))
                return;
            memoryValue = userInputValue;
            displayMemoryStat();
            hasFinalResult = true;
            break;
        default:
            if (Character.isDigit(text.charAt(0))) {
                if (currentInput.equals("0") || resetInput || hasFinalResult) {
                    userInputText.setText(text);
                    resetInput = false;
                    hasFinalResult = false;
                } else {
                    userInputText.append(text);
                    resetInput = false;
                }

            }
            break;

        }

    }

    private void clearStacks() {
        mInputStack.clear();
        mOperationStack.clear();
        mStackText.setText("");
    }

    private void dumpInputStack() {
        Iterator<String> it = mInputStack.iterator();
        StringBuilder sb = new StringBuilder();

        while (it.hasNext()) {
            CharSequence iValue = it.next();
            sb.append(iValue);

        }

        mStackText.setText(sb.toString());
    }

    private String evaluateResult(boolean requestedByUser) {
        if ((!requestedByUser && mOperationStack.size() != 4)
                || (requestedByUser && mOperationStack.size() != 3))
            return null;

        String left = mOperationStack.get(0);
        String operator = mOperationStack.get(1);
        String right = mOperationStack.get(2);
        String tmp = null;
        if (!requestedByUser)
            tmp = mOperationStack.get(3);

        double leftVal = Double.parseDouble(left.toString());
        double rightVal = Double.parseDouble(right.toString());
        double result = Double.NaN;

        if (operator.equals(KeypadButton.DIV.getText())) {
            result = leftVal / rightVal;
        } else if (operator.equals(KeypadButton.MULTIPLY.getText())) {
            result = leftVal * rightVal;

        } else if (operator.equals(KeypadButton.PLUS.getText())) {
            result = leftVal + rightVal;
        } else if (operator.equals(KeypadButton.MINUS.getText())) {
            result = leftVal - rightVal;

        }

        String resultStr = doubleToString(result);
        if (resultStr == null)
            return null;

        mOperationStack.clear();
        if (!requestedByUser) {
            mOperationStack.add(resultStr);
            mOperationStack.add(tmp);
        }

        return resultStr;
    }

    private String doubleToString(double value) {
        if (Double.isNaN(value))
            return null;

        long longVal = (long) value;
        if (longVal == value)
            return Long.toString(longVal);
        else
            return Double.toString(value);

    }

    private double tryParseUserInput() {
        String inputStr = userInputText.getText().toString();
        double result = Double.NaN;
        try {
            result = Double.parseDouble(inputStr);
        } catch (NumberFormatException nfe) {
        }

        return result;

    }

    private void displayMemoryStat() {
        if (Double.isNaN(memoryValue)) {
            memoryStatText.setText("");
        } else {
            memoryStatText.setText("M = " + doubleToString(memoryValue));
        }
    }

}

要查找输入数字的倒数，我使用以下代码：

    case INVERT:
    if (currentInput != "0") {
        userInputText.setText("1/" + currentInput);
    }
    break;

但是，不像我想要的那样显示倒数的输出，它只显示“1 /输入的数字”。为什么会这样，有人可以帮我解决这个问题吗？提前谢谢。

Answer 1

您将其作为文本返回，这就是它的显示方式。您需要进行数学运算，然后将其转换为字符串：

float input = Float.valueOf(currentInput);
if( input == 0)  // Check if 0 to avoid divide by 0 error
    userInputText.setText("NaN");
else
    userInputText.setText(Float.toString(1/input));

Answer 2

double inputVal = Double.valueOf(currentInput);
userInputText.setText(inputVal != 0 ? String.valueOf(1/inputVal) : "NaN");