android 监控EditText的变化

在玩android的时候，有时候需要这样的功能，在editText里输入字符，要实时的监控输入的内容，比如 我要获取手机的IMEI号码。最后要输入*#06#就可以获取到了。那这是如何做到呢？或者说Phone是如何实现这个功能的呢？

这主要用到了TextWatcher接口。

public class DialpadFragment extends Fragment
        implements View.OnClickListener,
        View.OnLongClickListener, View.OnKeyListener,
        AdapterView.OnItemClickListener, TextWatcher,
        PopupMenu.OnMenuItemClickListener,
        DialpadImageButton.OnPressedListener 

这个类是拨号界面的类。可以看到它就实现了TextWatcher

 public void beforeTextChanged(CharSequence s, int start, int count, int after) {
        mWasEmptyBeforeTextChange = TextUtils.isEmpty(s);
    }

    @Override
    public void onTextChanged(CharSequence input, int start, int before, int changeCount) {
        if (mWasEmptyBeforeTextChange != TextUtils.isEmpty(input)) {
            final Activity activity = getActivity();
            if (activity != null) {
                activity.invalidateOptionsMenu();
            }
        }

        // DTMF Tones do not need to be played here any longer -
        // the DTMF dialer handles that functionality now.
    }

    @Override
    public void afterTextChanged(Editable input) {
        // When DTMF dialpad buttons are being pressed, we delay SpecialCharSequencMgr sequence,
        // since some of SpecialCharSequenceMgr's behavior is too abrupt for the "touch-down"
        // behavior.
        if (!mDigitsFilledByIntent &&
                SpecialCharSequenceMgr.handleChars(getActivity(), input.toString(), mDigits)) {
            // A special sequence was entered, clear the digits
            mDigits.getText().clear();
        }

        if (isDigitsEmpty()) {
            mDigitsFilledByIntent = false;
            mDigits.setCursorVisible(false);
        }

        updateDialAndDeleteButtonEnabledState();
    }

判断输入的内容就是这句SpecialCharSequenceMgr.handleChars(getActivity(), input.toString(), mDigits))

进入了这里

static boolean handleIMEIDisplay(Context context, String input, boolean useSystemWindow) {
        if (input.equals(MMI_IMEI_DISPLAY)) {
            int subscription = MSimTelephonyManager.getDefault().getPreferredVoiceSubscription();
            int phoneType;
            if (MSimTelephonyManager.getDefault().isMultiSimEnabled()) {
                phoneType = ((MSimTelephonyManager)context.getSystemService(
                        Context.MSIM_TELEPHONY_SERVICE)).getCurrentPhoneType(subscription);
            } else {
                phoneType = ((TelephonyManager)context.getSystemService(
                        Context.TELEPHONY_SERVICE)).getCurrentPhoneType();
            }

            if (phoneType == TelephonyManager.PHONE_TYPE_GSM) {
                showIMEIPanel(context, useSystemWindow);
                return true;
            } else if (phoneType == TelephonyManager.PHONE_TYPE_CDMA) {
                showMEIDPanel(context, useSystemWindow);
                return true;
            }
        }

        return false;
    }

最后通过

        AlertDialog alert = new AlertDialog.Builder(context)
                .setTitle(R.string.imei)
                .setMessage(imeiStr)
                .setPositiveButton(android.R.string.ok, null)
                .setCancelable(false)
                .show();

显示出对话框了。