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