TextDialog.java中onTextChanged函數的解析

這幾天在尋找android  browser的一個bug時，發現這個函數停經典的，趕緊記錄下來，呵呵。

這裡我們以IME在www.google.com網頁的輸入框(TextDialog view)中輸入“弟弟ff”為例，首先假設已經輸入了“ff”。

為了輸入“弟弟”，使用者在IME的軟鍵盤上敲d字元兩次，然後“dd”會被聯想為“弟弟”，然後使用者在IME的備選框中選擇聯想得到的“弟弟”。 "dd"到“弟弟”這個步驟會導致如下函數被調用：

onTextChanged(CharSequence s,int start,int before,int count)

//參數s為“弟弟ff”     before為2，表示有兩個字元（“dd”）被刪掉了  count為 2，表示有兩個字元（“弟弟”）被添加了。

//before和count的含義在TextView（cupcake/frameworks/base/core/java/android/widget/TextView.java）的//onTextChanged函數中有注釋。

 

下面把這個函數代碼列出來並附加一點注釋

cupcake/frameworks/base/core/java/android/webkit/TextDialog.java:

protected void onTextChanged(CharSequence s,int start,int before,int count){
        super.onTextChanged(s, start, before, count);
        String postChange = s.toString();         //postChange為“弟弟ff”
        // Prevent calls to setText from invoking onTextChanged (since this will
        // mean we are on a different textfield).  Also prevent the change when
        // going from a textfield with a string of text to one with a smaller
        // limit on text length from registering the onTextChanged event.
        if (mPreChange == null || mPreChange.equals(postChange) ||
                (mMaxLength > -1 && mPreChange.length() > mMaxLength &&
                mPreChange.substring(0, mMaxLength).equals(postChange))) {
            return;
        }
        mPreChange = postChange;    //mPreChange之前的值為"ddff"
        // This was simply a delete or a cut, so just delete the
        // selection.

        //這段代碼不會執行，它用來處理刪除和剪下的。 請注意：在android browser中有一個資料結構render tree來     

        //表示資料，我們需要更新它，同時還有一個CachedText來表示TextDialog中的資料，兩個都需要更新。             

        //mWebView.deleteSelection(start, start + before)代碼更新了render tree這種底層資料, 而   

        //updateCachedTextfield();代碼更新了cached text。
        if (before > 0 && 0 == count) {
            mWebView.deleteSelection(start, start + before);
            // For this and all changes to the text, update our cache
            updateCachedTextfield();
            return;
        }
        // Find the last character being replaced.  If it can be represented by
        // events, we will pass them to native (after replacing the beginning
        // of the changed text), so we can see javascript events.
        // Otherwise, replace the text being changed (including the last
        // character) in the textfield.
        //這段注釋很好，“弟弟”中的最後一個字元“弟”不會從kmap中得到KeyEvent，所以（cannotUseKeyEvents＝0）

        //會直接調用mWebView.replaceTextfieldText()（更新browser下層的表示TextDialog的節點的string）把“dd”

        //替換為“dd”，同時updateCachedTextfield()被調用去更新cachedtext.因為“弟”不能被映射為一個KeyEvent，

        //所以  sendDomEvent(events[i])不會調用，沒有event被送給webkit中javascript部分。
        TextUtils.getChars(s, start + count - 1, start + count, mCharacter, 0);
        KeyCharacterMap kmap =
                KeyCharacterMap.load(KeyCharacterMap.BUILT_IN_KEYBOARD);
        KeyEvent[] events = kmap.getEvents(mCharacter);
        boolean cannotUseKeyEvents = null == events;
        int charactersFromKeyEvents = cannotUseKeyEvents ? 0 : 1;
        if (count > 1 || cannotUseKeyEvents) {
            String replace = s.subSequence(start,
                    start + count - charactersFromKeyEvents).toString();
            mWebView.replaceTextfieldText(start, start + before, replace,
                    start + count - charactersFromKeyEvents,
                    start + count - charactersFromKeyEvents);   //在browser底層“dd”替換為“弟弟”
        } else {
            // This corrects the selection which may have been affected by the
            // trackball or auto-correct.
            mWebView.setSelection(start, start + before);
        }
        updateCachedTextfield();   //把cached text中“dd”替換為“弟弟”
        if (cannotUseKeyEvents) {
            return;
        }
        int length = events.length;
        for (int i = 0; i < length; i++) {
            // We never send modifier keys to native code so don't send them
            // here either.
            if (!KeyEvent.isModifierKey(events[i].getKeyCode())) {
                sendDomEvent(events[i]);
            }
        }
    }