An EditTextPreference with Minimum character requirement

问题

I have an EditTextPreference that I user to allow use to set a passcode to an app. I want to require a 4-digit passcode. I set the maxLength = "4" in the xml file. Now I have the problem to not allow submit unless the entered passcode is 4 digits long.

Here is what I have:

 <EditTextPreference
            android:defaultValue=""
            android:dependency="EnablePasscode"
            android:dialogMessage="Add a numeric passcode to provide access to enter the app.  The passcode must be 4 digits."
            android:dialogTitle="Set Passcode"
            android:inputType="number"
            android:key="passcode"
            android:maxLength="4"
            android:password="true"
            android:title="Set Passcode" />

Now in Java:

public void onSharedPreferenceChanged(SharedPreferences sharedPreferences,
        String key) {

    if (key.equals("passcode")) {
        EditTextPreference setPasscode = (EditTextPreference) findPreference("passcode");
        if (setPasscode.getText().toString().length() == 4) {
            // return true
        }
    }

}

Where it says return true comment out, I am not sure how to handle this; I know I don't do a return; what I want it it to submit the Dialog Box if length is 4, otherwise if it is 0, 1, 2, or 3, throw a toast. Where and how can I do that?

UPDATE: TO validate this preference, I need control of the OK button which I do not have; this may be a workaround.

回答1:

private EditTextPreference preference;

this.preference = ((EditTextPreference) getPreferenceScreen() //put this in the onCreate                
                .findPreference("passcode"));

  if (key.equals("passcode")) {
        EditTextPreference setPasscode = (EditTextPreference) findPreference("passcode");
        if (sharedPreferences.getString("passcode","0").length() != 4) {
           Toast.makeText(this, "Should be 4 digits", Toast.LENGTH_LONG).show();
           this.preference.setText(null);
           return;
        }else{
              Toast.makeText(this, "Success!", Toast.LENGTH_LONG).show();
             }
    }

something like this should help you. Do keep in mind that getPreferenceScreen is deprecated, it is recommended to use PreferenceFragment. I am assuming that PreferenceActivity is being extended here.

来源：https://stackoverflow.com/questions/20820481/an-edittextpreference-with-minimum-character-requirement