我正在构建一个简单的 Android 计算器应用程序。事情进展顺利。后来我觉得我的代码很乱，决定重新整理和清理代码。我创建了一个新项目并将重新排列的代码复制到其中，但应用程序在启动后立即停止。这是代码:
package com.example.calculator_v001;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import java.util.ArrayList;
import java.util.List;
public class Calculator_v001_Activity extends Activity
{
boolean afterAns = false;
private EditText edtShow;
private Button btn0, btn1, btn2, btn3, btn4 ,btn5, btn6, btn7, btn8, btn9, btnPlus, btnMinus, btnTimes, btnDivide, btnEquals, btnDot, btnClear, btnBack;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.calculator_v001);
edtShow = (EditText)findViewById(R.id.edtShow);
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);
btnTimes = (Button)findViewById(R.id.btnTimes);
btnDivide = (Button)findViewById(R.id.btnDivide);
btnEquals = (Button)findViewById(R.id.btnEquals);
btnDot = (Button)findViewById(R.id.btnDot);
btnClear = (Button)findViewById(R.id.btnClear);
btnBack = (Button)findViewById(R.id.btnBack);
btn0.setOnClickListener(numListener);
btn1.setOnClickListener(numListener);
btn2.setOnClickListener(numListener);
btn3.setOnClickListener(numListener);
btn4.setOnClickListener(numListener);
btn5.setOnClickListener(numListener);
btn6.setOnClickListener(numListener);
btn7.setOnClickListener(numListener);
btn8.setOnClickListener(numListener);
btn9.setOnClickListener(numListener);
btnPlus.setOnClickListener(operListener);
btnMinus.setOnClickListener(operListener);
btnTimes.setOnClickListener(operListener);
btnDivide.setOnClickListener(operListener);
btnEquals.setOnClickListener(equalsListener);
btnDot.setOnClickListener(dotListener);
btnClear.setOnClickListener(clearListener);
btnBack.setOnClickListener(backListener);
}
private String addcomma(String str)
{
boolean dotdeleted = false;
if(str.length() != 0)
{
if(str.substring(str.length() - 1).equals("."))
{
str = str.substring(0, str.length() - 1);
dotdeleted = true;
}
}
List<String> numlistcomma = new ArrayList<String>();
List<String> tempsignlist = new ArrayList<String>();
String num = "";
for(int i = 0; i < str.length(); i++)
{
if(! checkPM(str.substring(i, i + 1)) && ! checkTD(str.substring(i, i + 1)))
{
num = num + str.substring(i, i + 1);
} else
{
numlistcomma.add(num);
tempsignlist.add(str.substring(i, i + 1));
num = "";
}
}
if(! num.equals(""))
{
numlistcomma.add(num);
}
for(int j = 0; j < numlistcomma.size(); j++)
{
String tempstr = numlistcomma.get(j);
if(! checkDot(numlistcomma.get(j)))
{
for(int k = numlistcomma.get(j).length() - 3; k > 0; k = k - 3)
{
tempstr = tempstr.substring(0, k) + "," + tempstr.substring(k);
}
} else
{
for(int k = numlistcomma.get(j).indexOf(".") - 3; k > 0; k = k - 3)
{
tempstr = tempstr.substring(0, k) + "," + tempstr.substring(k);
}
}
if(tempstr.length() != 0)
{
numlistcomma.set(j, tempstr);
}
}
str = "";
for(int l = 0; l < numlistcomma.size(); l++)
{
if(l < tempsignlist.size())
{
str = str + numlistcomma.get(l) + tempsignlist.get(l);
} else
{
str = str + numlistcomma.get(l);
}
}
if(dotdeleted)
{
str = str + ".";
}
return str;
};
private String calculate(String str)
{
String num = "";
String numlistele = "";
String tdAns = "";
List<String> list = new ArrayList<String>();
List<String> numlist = new ArrayList<String>();
List<String> TDlist = new ArrayList<String>();
for(int i = 0; i < str.length(); i++)
{
if(! checkPM(str.substring(i, i + 1)))
{
num = num + str.substring(i, i + 1);
} else
{
list.add(num);
list.add(str.substring(i, i + 1));
num = "";
}
}
list.add(num);
if(checkPM(list.get(list.size() - 1)))
{
list.remove(list.get(list.size() - 1));
}
for(int j = 0; j < list.size(); j++)
{
if(checkTD(list.get(j)))
{
for(int k = 0; k < list.get(j).length(); k++)
{
if(! checkTD(list.get(j).substring(k, k + 1)))
{
numlistele = numlistele + list.get(j).substring(k, k + 1);
} else
{
numlist.add(numlistele);
TDlist.add(list.get(j).substring(k, k + 1));
numlistele = "";
}
}
numlist.add(numlistele);
numlistele = "";
tdAns = numlist.get(0);
for(int l = 0; l < TDlist.size(); l++)
{
if(TDlist.get(l).equals("×"))
{
double tempdou = Double.parseDouble(tdAns) * Double.parseDouble(numlist.get(l + 1));
tdAns = String.valueOf(tempdou);
} else
{
double tempdou = Double.parseDouble(tdAns) / Double.parseDouble(numlist.get(l = 1));
tdAns = String.valueOf(tempdou);
}
}
list.set(j, tdAns);
}
numlist.clear();
TDlist.clear();
}
String ans = list.get(0);
for(int m = 0; m < list.size(); m++)
{
if(list.get(m).equals("+"))
{
double tempdou = Double.parseDouble(ans) + Double.parseDouble(list.get(m + 1));
ans = String.valueOf(tempdou);
} else if(list.get(m).equals("-"))
{
double tempdou = Double.parseDouble(ans) - Double.parseDouble(list.get(m = 1));
ans = String.valueOf(tempdou);
}
}
if(ans.length() > 2)
{
if(ans.substring(ans.length() - 2).equals(".0"))
{
ans = ans.substring(0, ans.length() - 2);
}
}
return ans;
};
private boolean checkDot(String str)
{
int count = 0;
if(checkPM(str) || checkTD(str))
{
for(int i = str.length(); ! checkPM(str.substring(i - 1, i)) && ! checkTD(str.substring(i - 1, i)); i--)
{
if(str.substring(i - 1, i).equals("."))
{
count++;
}
}
} else
{
for(int i = str.length(); i != 0; i--)
{
if(str.substring(i - 1, i).equals("."))
{
count++;
}
}
}
if(count != 0)
{
return true;
} else
{
return false;
}
};
private boolean checkPM(String str)
{
int count = 0;
for(int i = 0; i < str.length(); i++)
{
if(str.substring(i, i + 1).equals("+") || str.substring(i, i + 1).equals("-"))
{
count++;
}
}
if(count != 0)
{
return true;
} else
{
return false;
}
};
private boolean checkTD(String str)
{
int count = 0;
for(int i = 0; i < str.length(); i++)
{
if(str.substring(i, i + 1).equals("×") || str.substring(i, i + 1).equals("÷"))
{
count++;
}
}
if(count != 0)
{
return true;
} else
{
return false;
}
};
private void pressNum(String str, String n)
{
String tempstr = "";
if(str.length() == 0 || str.equals("0") || afterAns)
{
tempstr = n;
} else if(str.length() == 1)
{
tempstr = str + n;
} else
{
if(str.substring(str.length() - 1).equals("0") && (checkPM(str.substring(str.length() - 2, str.length() - 1)) || checkTD(str.substring(str.length() - 2, str.length() - 1))))
{
tempstr = str.substring(0, str.length() - 1) + n;
} else
{
tempstr = str + n;
}
}
edtShow.setText(addcomma(tempstr));
edtShow.setSelection(edtShow.getText().length());
afterAns = false;
};
private void pressOper(String str, String n)
{
String tempstr = "";
if(str.length() != 0)
{
if(! checkPM(str.substring(s.length() - 1)) && ! checkTD(str.substring(str.length() - 1)) && ! str.substring(s.length() - 1).equals("."))
{
tempstr = str + n;
} else
{
tempstr = str.substring(0, s.length() - 1) + n;
}
}
edtShow.setText(addcomma(tempstr));
edtShow.setSelection(edtShow.getText().length());
afterAns = false;
};
private String removecomma(String str)
{
for(int i = 0; i < str.length(); i++)
{
if(str.substring(i, i + 1).equals(","))
{
str = str.substring(0, i) + str.substring(i + 1);
}
}
return str;
};
String s = removecomma(edtShow.getText().toString());
private Button.OnClickListener numListener = new Button.OnClickListener()
{
public void onClick (View v)
{
switch(v.getId())
{
case R.id.btn0:
{
pressNum(s, "0");
break;
}
case R.id.btn1:
{
pressNum(s, "1");
break;
}
case R.id.btn2:
{
pressNum(s, "2");
break;
}
case R.id.btn3:
{
pressNum(s, "3");
break;
}
case R.id.btn4:
{
pressNum(s, "4");
break;
}
case R.id.btn5:
{
pressNum(s, "5");
break;
}
case R.id.btn6:
{
pressNum(s, "6");
break;
}
case R.id.btn7:
{
pressNum(s, "7");
break;
}
case R.id.btn8:
{
pressNum(s, "8");
break;
}
case R.id.btn9:
{
pressNum(s, "9");
break;
}
}
}
};
private Button.OnClickListener operListener = new Button.OnClickListener()
{
public void onClick (View v)
{
switch (v.getId())
{
case R.id.btnPlus:
{
pressOper(s, "+");
break;
}
case R.id.btnMinus:
{
pressOper(s, "-");
break;
}
case R.id.btnTimes:
{
pressOper(s, "×");
break;
}
case R.id.btnDivide:
{
pressOper(s, "÷");
break;
}
}
}
};
private Button.OnClickListener equalsListener = new Button.OnClickListener()
{
public void onClick (View v)
{
if(s.length() != 0)
{
if(! s.substring(s.length() - 1).equals(".") && (! checkPM(s.substring(s.length() - 1)) || ! checkTD(s.substring(s.length() - 1))))
{
edtShow.setText(addcomma(calculate(s)));
afterAns = true;
}
}
}
};
private Button.OnClickListener dotListener = new Button.OnClickListener()
{
public void onClick (View v)
{
String tempstr = "";
if(s.length() != 0 && ! checkDot(s) && ! checkPM(s.substring(s.length() - 1))&& ! checkTD(s.substring(s.length() - 1)))
{
tempstr = s + ".";
} else
{
tempstr = s;
}
edtShow.setText(addcomma(tempstr));
}
};
private Button.OnClickListener clearListener = new Button.OnClickListener()
{
public void onClick (View v)
{
edtShow.setText("");
}
};
private Button.OnClickListener backListener = new Button.OnClickListener()
{
public void onClick (View v)
{
if(s.length() == 0 || s.equals("NaN") || s.equals("Infinity"))
{
edtShow.setText("");
} else
{
edtShow.setText(addcomma(removecomma(s).substring(0, removecomma(s).length() - 1)));
edtShow.setSelection(edtShow.getText().length());
}
}
};
@Override
public boolean onCreateOptionsMenu(Menu menu)
{
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.calculator_v001_, menu);
return true;
}
}
堆栈跟踪:
07-08 12:00:40.917: E/Trace(913): error opening trace file: No such file or directory (2)
07-08 12:00:41.077: D/AndroidRuntime(913): Shutting down VM
07-08 12:00:41.097: W/dalvikvm(913): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
07-08 12:00:41.127: E/AndroidRuntime(913): FATAL EXCEPTION: main
07-08 12:00:41.127: E/AndroidRuntime(913): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.hychentsa.calculator_v001/com.hychentsa.calculator_v001.Calculator_v001_Activity}: java.lang.NullPointerException
07-08 12:00:41.127: E/AndroidRuntime(913): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2106)
07-08 12:00:41.127: E/AndroidRuntime(913): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
07-08 12:00:41.127: E/AndroidRuntime(913): at android.app.ActivityThread.access$600(ActivityThread.java:141)
07-08 12:00:41.127: E/AndroidRuntime(913): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
07-08 12:00:41.127: E/AndroidRuntime(913): at android.os.Handler.dispatchMessage(Handler.java:99)
07-08 12:00:41.127: E/AndroidRuntime(913): at android.os.Looper.loop(Looper.java:137)
07-08 12:00:41.127: E/AndroidRuntime(913): at android.app.ActivityThread.main(ActivityThread.java:5041)
07-08 12:00:41.127: E/AndroidRuntime(913): at java.lang.reflect.Method.invokeNative(Native Method)
07-08 12:00:41.127: E/AndroidRuntime(913): at java.lang.reflect.Method.invoke(Method.java:511)
07-08 12:00:41.127: E/AndroidRuntime(913): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
07-08 12:00:41.127: E/AndroidRuntime(913): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
07-08 12:00:41.127: E/AndroidRuntime(913): at dalvik.system.NativeStart.main(Native Method)
07-08 12:00:41.127: E/AndroidRuntime(913): Caused by: java.lang.NullPointerException
07-08 12:00:41.127: E/AndroidRuntime(913): at com.hychentsa.calculator_v001.Calculator_v001_Activity.<init>(Calculator_v001_Activity.java:332)
07-08 12:00:41.127: E/AndroidRuntime(913): at java.lang.Class.newInstanceImpl(Native Method)
07-08 12:00:41.127: E/AndroidRuntime(913): at java.lang.Class.newInstance(Class.java:1319)
07-08 12:00:41.127: E/AndroidRuntime(913): at android.app.Instrumentation.newActivity(Instrumentation.java:1054)
07-08 12:00:41.127: E/AndroidRuntime(913): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2097)
07-08 12:00:41.127: E/AndroidRuntime(913): ... 11 more
最佳答案
请检查代码的第 332 行。
String s = removecomma(edtShow.getText().toString());
这不应该在方法之外。它将被视为类变量并在创建 Activity 时实例化。此时 edtShow.getText() 为 nil。
关于java - Android 应用程序启动后立即停止，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/17525750/