Android activity生命周期二

本系列文章一共三篇，第一张讲activity正常生命周期，第二篇讲activity异常的生命周期

第二篇

当横屏切换为竖屏的时候，activity对象默认是会从新创建的，当然这个我们可以阻止它从新创建，（列如xml中写死屏幕方法，也可以代码设置，自行百度）

横竖屏切换（或者内存不够系统回收）

oncreate， onstart， onresume，onpasue，onstop，ondestroy，oncreate，onstart ，onresume.

需要了解两个方法

1， onSaveInstanceState(Bundle outState, PersistableBundle outPersistentState) 

调用时机、onstop 之前 ，这个方法的主要作用就是给我们保存之前的数据，我们可以在这个方法中去保存我们需要的数据，

2，onRestoreInstanceState(Bundle savedInstanceState)

调用时机；条件activity不是正常销毁，从新创建在onstart之后，这个方法回调的时候可以从bundle拿到我们之前保存的数据，当然也可从oncreate（Bundle savedInstanceState）方法中拿参数，但是如果正常创建bundle则会为空，所以需要判断才能用

其实google建议我们用这个方法onRestoreInstanceState(Bundle savedInstanceState)，只有异常销毁之后从新创建才会回调此方法

延伸，这种异常回收保存数据机制，view中也有 看textview源码

 @Override
    public Parcelable onSaveInstanceState() {
        Parcelable superState = super.onSaveInstanceState();

        // Save state if we are forced to
        final boolean freezesText = getFreezesText();
        boolean hasSelection = false;
        int start = -1;
        int end = -1;

        if (mText != null) {
            start = getSelectionStart();
            end = getSelectionEnd();
            if (start >= 0 || end >= 0) {
                // Or save state if there is a selection
                hasSelection = true;
            }
        }

        if (freezesText || hasSelection) {
            SavedState ss = new SavedState(superState);

            if (freezesText) {
                if (mText instanceof Spanned) {
                    final Spannable sp = new SpannableStringBuilder(mText);

                    if (mEditor != null) {
                        removeMisspelledSpans(sp);
                        sp.removeSpan(mEditor.mSuggestionRangeSpan);
                    }

                    ss.text = sp;
                } else {
                    ss.text = mText.toString();
                }
            }

            if (hasSelection) {
                // XXX Should also save the current scroll position!
                ss.selStart = start;
                ss.selEnd = end;
            }

            if (isFocused() && start >= 0 && end >= 0) {
                ss.frozenWithFocus = true;
            }

            ss.error = getError();

            if (mEditor != null) {
                ss.editorState = mEditor.saveInstanceState();
            }
            return ss;
        }

        return superState;
    }

textview数据恢复的源码

  @Override
    public void onRestoreInstanceState(Parcelable state) {
        if (!(state instanceof SavedState)) {
            super.onRestoreInstanceState(state);
            return;
        }

        SavedState ss = (SavedState) state;
        super.onRestoreInstanceState(ss.getSuperState());

        // XXX restore buffer type too, as well as lots of other stuff
        if (ss.text != null) {
            setText(ss.text);
        }

        if (ss.selStart >= 0 && ss.selEnd >= 0) {
            if (mText instanceof Spannable) {
                int len = mText.length();

                if (ss.selStart > len || ss.selEnd > len) {
                    String restored = "";

                    if (ss.text != null) {
                        restored = "(restored) ";
                    }

                    Log.e(LOG_TAG, "Saved cursor position " + ss.selStart + "/" + ss.selEnd
                            + " out of range for " + restored + "text " + mText);
                } else {
                    Selection.setSelection((Spannable) mText, ss.selStart, ss.selEnd);

                    if (ss.frozenWithFocus) {
                        createEditorIfNeeded();
                        mEditor.mFrozenWithFocus = true;
                    }
                }
            }
        }

        if (ss.error != null) {
            final CharSequence error = ss.error;
            // Display the error later, after the first layout pass
            post(new Runnable() {
                public void run() {
                    if (mEditor == null || !mEditor.mErrorWasChanged) {
                        setError(error);
                    }
                }
            });
        }

        if (ss.editorState != null) {
            createEditorIfNeeded();
            mEditor.restoreInstanceState(ss.editorState);
        }
    }

这种保存的机制大概原理就是，activity异常回收的时候，会调用onsaveinstace方法，然后委托window 去保存数据，window再去委托decorview去保存数据，最后decorview在一一遍历子元素 去保存数据，典型的委托思想这样数据就全部保存了