[英]Why my .isEmpty does not work in this code?
我想编程检查用户是否在按下按钮之前写下要检查的数字。
public class MainActivity extends AppCompatActivity {
int randomNumber;
public void makeToast(String string) {
Toast.makeText(MainActivity.this, string, Toast.LENGTH_LONG).show();
}
public void guess (View view) {
final EditText showNumber = findViewById(R.id.showNumberEditText);
int guessInt = Integer.parseInt(showNumber.getText().toString());
if (showNumber.getText().toString().isEmpty()) {
makeToast("Pleas Enter a Number!");
} else if(guessInt > randomNumber) {
makeToast("Lower");
} else if (guessInt < randomNumber) {
makeToast("Higher");
} else {
makeToast("Correct! Try Again!");
Random random = new Random();
randomNumber = random.nextInt(20) + 1;
}
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Random random = new Random();
randomNumber = random.nextInt(20) + 1;
}
}
您必须考虑 EditText 可能尚未设置任何值,因此本质上可能包含Null ,因此.toString().isEmpty()可能会因NullPointerException而失败。 另外如果有文字,还需要考虑到它甚至可能不是数字,所以需要转换成integer。 并且字符串不能直接与整数进行比较,因此需要这种 integer 转换势在必行。
试试下面的代码:
public void guess (View view) {
final EditText showNumber = findViewById(R.id.showNumberEditText);
Integer guessInt = convertToInteger(showNumber.getText());
if (guessInt == null) {
makeToast("Pleas Enter a Number!");
}else if(guessInt > randomNumber) {
makeToast("Lower");
} else if (guessInt < randomNumber) {
makeToast("Higher");
} else {
makeToast("Correct! Try Again!");
Random random = new Random();
randomNumber = random.nextInt(20) + 1;
}
}
public static Integer convertToInteger(final Editable source) {
if (source != null) {
try {
final String text = source.toString();
return Integer.parseInt(text);
}
catch (NumberFormatException ex) {
ex.printStackTrace();
}
}
return null;
}
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