我正在尝试通过在字段中输入金额，在微调器中选择from currency，在另一个微调器中选择to currency来创建美元，英镑和欧元的简单货币转换器。然后我在文本字段中输出转换后的金额。
但由于某种原因，我无法超越onClick方法，我不知道为什么。它可能很简单，但我看不到它。
这是我的代码：
public class Calculate extends Activity implements OnItemSelectedListener,
OnClickListener {
Button Calculate;
String stringAmount;
double exchangeRate, E, D, Answer;
EditText Amount;
Spinner spinner, spinner1;
int ConvertFrom, ConvertTo;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.calculate);
Initilise();
// this is calling the method initilise.
// listens for the button to be clicked
Calculate.setOnClickListener(this);
}
private void Initilise() {
// Method initilise.
/* Button */Calculate = (Button) findViewById(R.id.cal);
/* EditText */Amount = (EditText) findViewById(R.id.amount);
spinner = (Spinner) findViewById(R.id.Currency);
spinner1 = (Spinner) findViewById(R.id.Currency1);
}
public void format() {
ConvertFrom = 0;
ConvertTo = 0;
stringAmount = Amount.getText().toString();
E = 0; // set it to 0 as the default
try {
E = Integer.parseInt(stringAmount);
} catch (NumberFormatException e) {
}
}
@SuppressWarnings("deprecation")
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
spinner();
switch (v.getId()) {
case R.id.cal:
if (ConvertFrom == 0) {
FromEuro();
} else if (ConvertFrom == 1) {
FromUsd();
} else if (ConvertFrom == 2) {
FromGbp();
} else {
// Amount.setText("Invalid Input");
AlertDialog alertDialog = new AlertDialog.Builder(this)
.create();
alertDialog.setTitle("Input");
alertDialog.setMessage("Please Input a amount");
alertDialog.setButton("OK",
new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog,
int which) {
// here you can add functions
}
});
alertDialog.setIcon(R.drawable.ic_launcher);
alertDialog.show();
}
}
}
public void spinner() {
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_spinner_item, R.array.Currencies);
spinner = (Spinner) findViewById(R.id.Currency);
spinner.setAdapter(adapter);
spinner.setOnItemSelectedListener(this);
spinner1 = (Spinner) findViewById(R.id.Currency1);
spinner1.setAdapter(adapter);
spinner1.setOnItemSelectedListener(this);
}
@Override
public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2,
long arg3) {
// TODO Auto-generated method stub
int posistion = spinner.getSelectedItemPosition();
ConvertFrom = posistion;
int posistion1 = spinner1.getSelectedItemPosition();
ConvertTo = posistion1;
}
@Override
public void onNothingSelected(AdapterView<?> arg0) {
// TODO Auto-generated method stub
}
@SuppressWarnings("deprecation")
private void FromEuro() {
// TODO Auto-generated method stub
if (ConvertTo == 1) {
exchangeRate = 1.336891;
Answer = E * exchangeRate;
String Final = Double.toString(Answer);
Amount.setText(Final);
} else if (ConvertTo == 2) {
exchangeRate = 1.336891;
Answer = E * exchangeRate;
String Final = Double.toString(Answer);
Amount.setText(Final);
} else if (ConvertTo == 0) {
AlertDialog alertDialog = new AlertDialog.Builder(null).create();
alertDialog.setTitle("Input");
alertDialog.setMessage("Please Select a gender");
alertDialog.setButton("OK", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
// here you can add functions
}
});
alertDialog.setIcon(R.drawable.ic_launcher);
alertDialog.show();
}
}
@SuppressWarnings("deprecation")
private void FromUsd() {
// TODO Auto-generated method stub
if (ConvertTo == 0) {
exchangeRate = 1.336891;
Answer = E * exchangeRate;
String Final = Double.toString(Answer);
Amount.setText(Final);
} else if (ConvertTo == 1) {
exchangeRate = 1.336891;
Answer = E * exchangeRate;
String Final = Double.toString(Answer);
Amount.setText(Final);
} else {
if (ConvertTo == 2) {
AlertDialog alertDialog = new AlertDialog.Builder(null)
.create();
alertDialog.setTitle("Input");
alertDialog.setMessage("Please Select a gender");
alertDialog.setButton("OK",
new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog,
int which) {
// here you can add functions
}
});
alertDialog.setIcon(R.drawable.ic_launcher);
alertDialog.show();
}
}
}
private void FromGbp() {
// TODO Auto-generated method stub
if (ConvertTo == 2) {
exchangeRate = 1.336891;
Answer = E * exchangeRate;
String Final = Double.toString(Answer);
Amount.setText(Final);
} else if (ConvertTo == 0) {
exchangeRate = 1.336891;
Answer = E * exchangeRate;
String Final = Double.toString(Answer);
Amount.setText(Final);
} else {
if (ConvertTo == 1) {
Builder alertDialog = new AlertDialog.Builder(this);
alertDialog.setTitle("Input");
alertDialog.setMessage("Please Select a gender");
alertDialog.setPositiveButton("OK",
new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog,
int which) {
// here you can add functions
}
});
alertDialog.setIcon(R.drawable.ic_launcher);
alertDialog.show();
}
}
}`
}
但我现在正在接收
02-19 16：55：01.514：E / AndroidRuntime（28638）：在android.app.AlertDialog.resolveDialogTheme（AlertDialog.java:142）
以上错误。
此前此问题出现以下错误：
想知道是否有人可以提供帮助。我得到这些错误：
FATAL EXCEPTION: main
java.lang.NullPointerException
at com.travelcurrencyconverter.Calculate.onClick(Calculate.java:64)
at android.view.View.performClick(View.java:4222)
at android.view.View$PerformClick.run(View.java:17273)
at android.os.Handler.handleCallback(Handler.java:615)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4895)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:994)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:761)
at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：1)
您正尝试访问第64行null的引用成员（点前部分）。
此外，当您发布代码时，将所有内容缩进四个空格以使其全部语法变为彩色。
此外，在执行此操作之前，请确保在IDE中自动格式化代码。