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。