private static int sSmsToMmsTextThreshold = 6; // 4

vendor/mediatek/proprietary/packages/apps/Mms/res/layout/compose_message_activity.xml

vendor/mediatek/proprietary/packages/apps/Mms/src/com/android/mms/ui/ComposeMessageActivity.java
 private EnhanceEditText mTextEditor;      // Text editor to type your message into //消息輸入框
  private TextView mTextCounter;     // Shows the number of characters used in text editor //剩余字數顯示
  private TextView mSendButtonMms;    // Press to send mms //彩信發(fā)送按鈕，TextView中加入圖片
  private ImageButton mSendButtonSms;   // Press to send sms //短信發(fā)送按鈕
  private void updateCounter(CharSequence text, int start, int before, int count) {
    ...
    int[] params = null;
    int encodingType = SmsMessage.ENCODING_UNKNOWN;
    encodingType = mOpComposeExt.getSmsEncodingType(encodingType, ComposeMessageActivity.this);
    params = SmsMessage.calculateLength(text, false, encodingType);
      /* SmsMessage.calculateLength returns an int[4] with:
       *  int[0] being the number of SMS's required,
       *  int[1] the number of code units used,
       *  int[2] is the number of code units remaining until the next message.
       *  int[3] is the encoding type that should be used for the message.
       */
    final int msgCount = params[0]; //已輸入短信條數
    final int remainingInCurrentMessage = params[2]; //剩余字數
    mWorkingMessage.setLengthRequiresMms(
      msgCount >= MmsConfig.getSmsToMmsTextThreshold(), true); //轉為彩信的短信條數
    MmsLog.d(TAG, "updateCounter(): message msgCount = " + msgCount
        + " TextThreshold() = " + MmsConfig.getSmsToMmsTextThreshold()
        + " remainingInCurrentMessage = " + remainingInCurrentMessage);
    /// M: Show the counter
    /// M: Update the remaining characters and number of messages required.
    if (msgCount >= MmsConfig.getSmsToMmsTextThreshold()) {
      mTextCounter.setVisibility(View.GONE);
      return;
    }
    mUiHandler.postDelayed(new Runnable() {
      @Override
      public void run() {
        if (mOpComposeExt.updateCounterUiRun(mTextEditor, remainingInCurrentMessage,
            msgCount, mWorkingMessage)) {
          return;
        }
        MmsLog.d(TAG, "updateCounter requiresMms = " + mWorkingMessage.requiresMms()
            + " line count = " + mTextEditor.getLineCount());
        if (mWorkingMessage.requiresMms() || mTextEditor.getLineCount() <= 1) {
          mTextCounter.setVisibility(View.GONE);
          return;
        }
        mTextCounter.setVisibility(View.VISIBLE);
        String counterText = remainingInCurrentMessage + "/" + msgCount;
        mTextCounter.setText(counterText);
      }
    }, 100);
//顯示短信發(fā)送按鈕或彩信發(fā)送按鈕
  private View showSmsOrMmsSendButton(boolean isMms) {
    View showButton = null;
    View hideButton = null;
    // add for ipmessage
    if (isMms) {
      if (mSubCount == 0 || (isRecipientsEditorVisible()
          && TextUtils.isEmpty(mRecipientsEditor.getText()))
          /// M: fix bug ALPS00563318, show gray mms_send_button
        /// when haven't subject, text and attachment
        || ((mSubjectTextEditor == null || (mSubjectTextEditor != null
            && TextUtils.isEmpty(mSubjectTextEditor.getText().toString().trim())))
            && mTextEditor != null
            && TextUtils.isEmpty(mTextEditor.getText().toString().trim())
            && !mWorkingMessage.hasAttachment())
            || !mIsSmsEnabled) {
      mSendButtonMms.setCompoundDrawablesWithIntrinsicBounds(null, null, null,
        getResources().getDrawable(R.drawable.ic_send_sms_unsend));
    } else {
      mSendButtonMms.setCompoundDrawablesWithIntrinsicBounds(null, null, null,
          getResources().getDrawable(R.drawable.ic_send_ipmsg));
      }
      showButton = mSendButtonMms;
      hideButton = mSendButtonSms;
    } else {
      if (!mIpCompose.onIpShowSmsOrMmsSendButton(isMms)) {
        if ((mTextEditor.getText().toString().isEmpty())
            || mSubCount == 0
            || (isRecipientsEditorVisible()
                && TextUtils.isEmpty(mRecipientsEditor.getText()))
            || recipientCount() > MmsConfig.getSmsRecipientLimit()
            || !mIsSmsEnabled) {
          ///@}
          mSendButtonSms.setImageResource(R.drawable.ic_send_sms_unsend);
        } else {
          mSendButtonSms.setImageResource(R.drawable.ic_send_ipmsg);
        }
      }
      showButton = mSendButtonSms;
      hideButton = mSendButtonMms;
    }
    if (showButton != null) {
      showButton.setVisibility(View.VISIBLE);
    }
    if (hideButton != null) {
      hideButton.setVisibility(View.GONE);
    }
    updateTextEditorHint();
    return showButton;
  }