新建MMS草稿保存后，再进入草稿修改收件人，退出到会话界面，会显示两条草稿

分析原因：新建彩信草稿，保存后，再打开草稿，修改收件人，再保存会产生新的threadId, 而之前保存的草稿theadId还存在，导致此问题。

（必现。 解决方法：将原来的Thread_id和新的收件人传递到Provider，对收件人进行更新，避免生成新的Thread）

MMS草稿保存

private void asyncUpdateDraftMmsMessage(final Conversation conv, final boolean isStopping) {
        if (Log.isLoggable(LogTag.APP, Log.VERBOSE)) {
            LogTag.debug("asyncUpdateDraftMmsMessage conv=%s mMessageUri=%s", conv, mMessageUri);
        }
        final HashMap<Uri, InputStream> preOpenedFiles =
                mSlideshow.openPartFiles(mContentResolver);

        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    DraftCache.getInstance().setSavingDraft(true);

                    final PduPersister persister = PduPersister.getPduPersister(mActivity);
                    final SendReq sendReq = makeSendReq(conv, mSubject);
                    persister.setMmsDraftThreadId(mOldMmsDraftThreadId);//add by antoon, send old thread_id to pdu
                    
                    if (mMessageUri == null) {
                        mMessageUri = createDraftMmsMessage(persister, sendReq, mSlideshow, null,
                                mActivity, preOpenedFiles);//对于MMS保存，thread_id会在pdu保存时创建
                    } else {
                        updateDraftMmsMessage(mMessageUri, persister, mSlideshow, sendReq,
                                preOpenedFiles);//修改之前保存的MMS后，pdu更新数据，这里会根据收件人getOrCreateThreadId,所以修改收件人会导致创建新的thread
                    }
                    ensureThreadIdIfNeeded(conv, isStopping);//这里确认thread_id创建或获取成功，否则再次执行getOrCreateThreadId
                    conv.setDraftState(true);
                    if (Log.isLoggable(LogTag.APP, Log.VERBOSE)) {
                        LogTag.debug("asyncUpdateDraftMmsMessage conv: " + conv +
                                " uri: " + mMessageUri);
                    }

                    // Be paranoid and delete any SMS drafts that might be lying around. Must do
                    // this after ensureThreadId so conv has the correct thread id.
                    asyncDeleteDraftSmsMessage(conv);
                } finally {
                    DraftCache.getInstance().setSavingDraft(false);
                    closePreOpenedFiles(preOpenedFiles);
                }
            }
        }, "WorkingMessage.asyncUpdateDraftMmsMessage").start();
    }

看看  ensureThreadIdIfNeeded(conv, isStopping)

private void ensureThreadIdIfNeeded(final Conversation conv, final boolean isStopping) {
        if (isStopping && conv.getMessageCount() == 0) {
            // We need to save the drafts in an unorphaned thread id. When the user goes
            // back to ConversationList while we're saving a draft from CMA's.onStop,
            // ConversationList will delete all threads from the thread table that
            // don't have associated sms or pdu entries. In case our thread got deleted,
            // well call clearThreadId() so ensureThreadId will query the db for the new
            // thread.
            conv.clearThreadId();   // force us to get the updated thread id
        }
        if (!conv.getRecipients().isEmpty()) {
            conv.ensureThreadId();
        }
    }

public synchronized void clearThreadId() {
        // remove ourself from the cache
        if (Log.isLoggable(LogTag.APP, Log.VERBOSE)) {
            LogTag.debug("clearThreadId old threadId was: " + mThreadId + " now zero");
        }
        Cache.remove(mThreadId);

        mThreadId = 0;
}

public synchronized long ensureThreadId() {
        if (DEBUG || DELETEDEBUG) {
            LogTag.debug("ensureThreadId before: " + mThreadId);
        }
        if (mThreadId <= 0) {
            if (mIsGroupChat && mGroupChat != null) {
                HashSet<String> numbers = new HashSet<String>();
                numbers.add(String.valueOf(mGroupChat.getThreadId()));
                ContactList groupRecip = ContactList.getByNumbers(numbers, false);
                mThreadId = getOrCreateThreadId(mContext, groupRecip, mIsGroupChat);
            } else {
                mThreadId = getOrCreateThreadId(mContext, mRecipients, mIsGroupChat);
            }
        }
        if (DEBUG || DELETEDEBUG) {
            LogTag.debug("ensureThreadId after: " + mThreadId);
        }

        return mThreadId;
}

对于MMS， SMS草稿保存时都会调用 ensureThreadIdIfNeeded  ， 如果修改了收件人，应该都会有thread_id重建，获取操作。

但是对于SMS却没有反馈此问题，是怎么回事呢？

——原因：sms草稿会在重新打开时，将数据库删掉。重新保存草稿时，重新插入数据。 而MMS草稿在重新打开时，不会将数据库删除，修改收件人后，重新创建thread，导致此Bug。

     但sms草稿的处理方式，重新打开sms草稿，即使不修改，再次保存时，也会重新创建数据库数据。