我是Android新手，我正在调试这几个小时。我正在尝试检查空输入，我搜索stackoverflow寻找解决方案，但我找不到正确答案这里是我的代码。我的应用程序总是崩溃而不显示catch块上的内容。
public class LengthActivity extends ActionBarActivity {
Length len = new DoLengthConversion();
Spinner spinner;
Button getAnswer;
EditText userInput;
TextView um;
TextView mm;
TextView cm;
TextView dm;
TextView m;
TextView km;
TextView inch;
TextView ft;
TextView yd;
TextView mile;
TextView nm;
double input;
String[] units = { "micrometer", "millimeter", "centimeter", "decimeter", "meter", "kilometer", "inch", "feet", "yard", "mile", "nanometer" };
@Override
protected void onCreate(Bundle savedInstanceState) {
try {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_length);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
spinner = (Spinner) findViewById(R.id.spinner);
getComboBox();
initControls();
} catch (NumberFormatException e) {
AlertDialog.Builder ex = new AlertDialog.Builder(this);
ex.setTitle("Error Encountered: ");
ex.setMessage(e.getMessage());
ex.setCancelable(true);
ex.setPositiveButton("OK", null);
ex.setNegativeButton("Report problem", null);
ex.create().show();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_length, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
Intent back = new Intent(getApplicationContext(), BasicActivity.class);
startActivityForResult(back, 0);
overridePendingTransition(R.anim.abc_fade_in, R.anim.abc_fade_out);
finish();
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
// noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public void initControls() {
try {
userInput = (EditText) findViewById(R.id.userInput);
initiateTextViews();
getAnswer = (Button) findViewById(R.id.getAnswer);
getAnswer.setOnClickListener(new Button.OnClickListener() {
public void onClick(View v) {
input = Double.parseDouble(userInput.getText().toString());
int pos = spinner.getSelectedItemPosition();
if (pos == 0) {
printMicronConversions();
} else if (pos == 1) {
printMillimeterConversions();
} else if (pos == 2) {
printCentimeterConversions();
} else if (pos == 3) {
printDecimeterConversions();
} else if (pos == 4) {
printMeterConversions();
} else if (pos == 5) {
printKilometerConversions();
} else if (pos == 6) {
printInchConversions();
} else if (pos == 7) {
printFtConversion();
} else if (pos == 8) {
printYdConversion();
} else if (pos == 9) {
printMileConversion();
} else if (pos == 10) {
printNmConversion();
}
}
});
} catch (NumberFormatException e) {
AlertDialog.Builder ex = new AlertDialog.Builder(this);
ex.setTitle("Error Encountered: ");
ex.setMessage(e.getMessage());
ex.setCancelable(true);
ex.setPositiveButton("OK", null);
ex.setNegativeButton("Report problem", null);
ex.create().show();
}
}
private void initiateTextViews() {
um = (TextView) findViewById(R.id.um);
mm = (TextView) findViewById(R.id.mm);
cm = (TextView) findViewById(R.id.cm);
dm = (TextView) findViewById(R.id.dm);
m = (TextView) findViewById(R.id.m);
km = (TextView) findViewById(R.id.km);
inch = (TextView) findViewById(R.id.inch);
ft = (TextView) findViewById(R.id.ft);
yd = (TextView) findViewById(R.id.yd);
mile = (TextView) findViewById(R.id.miles);
nm = (TextView) findViewById(R.id.nm);
}
private void getComboBox() {
try {
ArrayAdapter<String> adapter = new ArrayAdapter<>(this, android.R.layout.simple_spinner_item, units);
spinner.setAdapter(adapter);
spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
}
@Override
public void onNothingSelected(AdapterView<?> parent) {
}
});
} catch (ArrayIndexOutOfBoundsException e) {
AlertDialog.Builder ex = new AlertDialog.Builder(this);
ex.setTitle("Error Encountered: ");
ex.setMessage(e.toString());
ex.setCancelable(true);
ex.setPositiveButton("OK", null);
ex.setNegativeButton("Report problem", null);
ex.create().show();
}
}
}
/**/
我尝试的是if(Double.toString(input).equals("")){}，但没有运气。编译器告诉我invalid double:""。
答案 0 :(得分：1)
只是一个简单的检查文本框是否具有值。
.........
public void onClick(View v)
{
if(!userInput.getText().toString().trim().equals(""))
{
//Write your code here...
try
{
input = Double.parseDouble(userInput.getText().toString());
}
catch(Exception ex)
{
//Handle exception here.....
}
}
}
.
.