我正在尝试构建一个基本的计算器。代码很好（我猜）。我在运行时没有收到任何错误，eclipse成功编译它。几乎一切都很好但是当我在editText视图中输入数字然后尝试通过点击＆＃34;计算＆＃34;来做一些计算。按钮应用程序崩溃。这是崩溃应用程序的代码：
private OnClickListener calcListener = new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
String f = first.getText().toString();
String s = second.getText().toString();
float fValue = Float.valueOf(f);
float sValue = Float.valueOf(s);
if((f.length() == 0) || (s.length() == 0))
Toast.makeText(MainActivity.this, "Please enter data in the first section", Toast.LENGTH_LONG).show();
else{
switch(sign.getCheckedRadioButtonId())
{
case R.id.mult:
float res_Mult = fValue*sValue;
result.setText(String.valueOf(res_Mult));
case R.id.plus:
float res_Add = fValue*sValue;
result.setText(String.valueOf(res_Add));
case R.id.minus:
float res_Minus = fValue*sValue;
result.setText(String.valueOf(res_Minus));
case R.id.div :
float res_Div = fValue*sValue;
result.setText(String.valueOf(res_Div));
}// end switch
}// end else
}
};// end onclik
Listener
问题似乎是计算，因为我试图输出＆＃34;你好＆＃34;在textview上，一旦按钮＆＃34;计算＆＃34;该文本视图应该显示计算结果。点击它就可以了。
Button calc = null;
EditText first = null;
EditText second = null;
RadioGroup sign = null;
TextView result = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//binding
calc = (Button) findViewById(R.id.calc);// the "calculate" button
first = (EditText) findViewById(R.id.first); //the first EditText
second = (EditText) findViewById(R.id.second);//the second EditText
result = (TextView) findViewById(R.id.result);// The textView that this supposed to display the result.
//setting listeners
calc.setOnClickListener(calcListener);
first.addTextChangedListener(watcher);
second.addTextChangedListener(watcher);
}
private TextWatcher watcher = new TextWatcher() {
@Override
public void onTextChanged(CharSequence s, int start, int before, int count) {
// TODO Auto-generated method stub
result.setText(" ");
}
@Override
public void beforeTextChanged(CharSequence s, int start, int count,
int after) {
// TODO Auto-generated method stub
}
@Override
public void afterTextChanged(Editable s) {
// TODO Auto-generated method stub
}
};// end textWatcher
这是logCat：
08-29 19:18:29.323: D/dalvikvm(1951): Not late-enabling CheckJNI (already on)
08-29 19:18:31.593: D/dalvikvm(1951): GC_FOR_ALLOC freed 72K, 10% free 2892K/3192K, paused 108ms, total 111ms
08-29 19:18:32.183: D/libEGL(1951): loaded /system/lib/egl/libEGL_emulation.so
08-29 19:18:32.213: D/(1951): HostConnection::get() New Host Connection established 0xb8cfd430, tid 1951
08-29 19:18:32.223: D/libEGL(1951): loaded /system/lib/egl/libGLESv1_CM_emulation.so
08-29 19:18:32.233: D/libEGL(1951): loaded /system/lib/egl/libGLESv2_emulation.so
08-29 19:18:32.313: W/EGL_emulation(1951): eglSurfaceAttrib not implemented
08-29 19:18:32.323: D/OpenGLRenderer(1951): Enabling debug mode 0
08-29 19:18:50.674: D/AndroidRuntime(1951): Shutting down VM
08-29 19:18:50.674: W/dalvikvm(1951): threadid=1: thread exiting with uncaught exception (group=0xb0eb8648)
08-29 19:18:50.724: E/AndroidRuntime(1951): FATAL EXCEPTION: main
08-29 19:18:50.724: E/AndroidRuntime(1951): java.lang.NullPointerException
08-29 19:18:50.724: E/AndroidRuntime(1951): at com.example.gets.calculator.MainActivity$2.onClick(MainActivity.java:76)
08-29 19:18:50.724: E/AndroidRuntime(1951): at android.view.View.performClick(View.java:4240)
08-29 19:18:50.724: E/AndroidRuntime(1951): at android.view.View$PerformClick.run(View.java:17721)
08-29 19:18:50.724: E/AndroidRuntime(1951): at android.os.Handler.handleCallback(Handler.java:730)
08-29 19:18:50.724: E/AndroidRuntime(1951): at android.os.Handler.dispatchMessage(Handler.java:92)
08-29 19:18:50.724: E/AndroidRuntime(1951): at android.os.Looper.loop(Looper.java:137)
08-29 19:18:50.724: E/AndroidRuntime(1951): at android.app.ActivityThread.main(ActivityThread.java:5103)
08-29 19:18:50.724: E/AndroidRuntime(1951): at java.lang.reflect.Method.invokeNative(Native Method)
08-29 19:18:50.724: E/AndroidRuntime(1951): at java.lang.reflect.Method.invoke(Method.java:525)
08-29 19:18:50.724: E/AndroidRuntime(1951): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
08-29 19:18:50.724: E/AndroidRuntime(1951): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
08-29 19:18:50.724: E/AndroidRuntime(1951): at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：1)
您的switch语句没有中断。这是一个错误，它会导致每个案例都落到下一个案例中，并在其下面的所有案例中执行每一段代码。
switch(sign.getCheckedRadioButtonId()) {
case R.id.mult:
float res_Mult = fValue*sValue;
result.setText(String.valueOf(res_Mult));
case R.id.plus:
float res_Add = fValue*sValue;
result.setText(String.valueOf(res_Add));
case R.id.minus:
float res_Minus = fValue*sValue;
result.setText(String.valueOf(res_Minus));
case R.id.div :
float res_Div = fValue*sValue;
result.setText(String.valueOf(res_Div));
}// end switch