android中finish()和onDestroy()的关系

一、activity的onDestroy()函数

Google解释：

    /**
     * Perform any final cleanup before an activity is destroyed.  This can
     * happen either because the activity is finishing (someone called
     * {@link #finish} on it, or because the system is temporarily destroying
     * this instance of the activity to save space.  You can distinguish
     * between these two scenarios with the {@link #isFinishing} method.
     * 
     * <p><em>Note: do not count on this method being called as a place for
     * saving data! For example, if an activity is editing data in a content
     * provider, those edits should be committed in either {@link #onPause} or
     * {@link #onSaveInstanceState}, not here.</em> This method is usually implemented to
     * free resources like threads that are associated with an activity, so
     * that a destroyed activity does not leave such things around while the
     * rest of its application is still running.  There are situations where
     * the system will simply kill the activity's hosting process without
     * calling this method (or any others) in it, so it should not be used to
     * do things that are intended to remain around after the process goes
     * away.
     * 
     * <p><em>Derived classes must call through to the super class's
     * implementation of this method.  If they do not, an exception will be
     * thrown.</em></p>
     * 
     * @see #onPause
     * @see #onStop
     * @see #finish
     * @see #isFinishing
     */

说白了onDestroy就是释放资源作用的。

源代码：

  protected void onDestroy() {
        mCalled = true;


        // dismiss any dialogs we are managing.
        if (mManagedDialogs != null) {
            final int numDialogs = mManagedDialogs.size();
            for (int i = 0; i < numDialogs; i++) {
                final ManagedDialog md = mManagedDialogs.valueAt(i);
                if (md.mDialog.isShowing()) {
                    md.mDialog.dismiss();
                }
            }
            mManagedDialogs = null;
        }


        // close any cursors we are managing.
        synchronized (mManagedCursors) {
            int numCursors = mManagedCursors.size();
            for (int i = 0; i < numCursors; i++) {
                ManagedCursor c = mManagedCursors.get(i);
                if (c != null) {
                    c.mCursor.close();
                }
            }
            mManagedCursors.clear();
        }


        // Close any open search dialog
        if (mSearchManager != null) {
            mSearchManager.stopSearch();
        }


        getApplication().dispatchActivityDestroyed(this);
    }

可以看见在调用 getApplication().dispatchActivityDestroyed(this)之前，有三个for循环，分别释放了activity中的dialogs，cursors 和 search dialog。最后调用Application的dispatchActivityDestroyed(this)。我们再来看看这个函数

dispatchActivityDestroyed()源码：

    /* package */ void dispatchActivityDestroyed(Activity activity) {
        Object[] callbacks = collectActivityLifecycleCallbacks();
        if (callbacks != null) {
            for (int i=0; i<callbacks.length; i++) {
                ((ActivityLifecycleCallbacks)callbacks[i]).onActivityDestroyed(activity);
            }
        }
    }

越来越深，以后再研究吧

二、finish()

/**
     * Call this when your activity is done and should be closed.  The
     * ActivityResult is propagated back to whoever launched you via
     * onActivityResult().
     */
    public void finish() {
        if (mParent == null) {
            int resultCode;
            Intent resultData;
            synchronized (this) {
                resultCode = mResultCode;
                resultData = mResultData;
            }
            if (false) Log.v(TAG, "Finishing self: token=" + mToken);
            try {
                if (resultData != null) {
                    resultData.setAllowFds(false);
                }
                if (ActivityManagerNative.getDefault()
                    .finishActivity(mToken, resultCode, resultData)) {
                    mFinished = true;
                }
            } catch (RemoteException e) {
                // Empty
            }
        } else {
            mParent.finishFromChild(this);
        }
    }


    /**
     * This is called when a child activity of this one calls its 
     * {@link #finish} method.  The default implementation simply calls
     * finish() on this activity (the parent), finishing the entire group.
     * 
     * @param child The activity making the call.
     * 
     * @see #finish
     */
    public void finishFromChild(Activity child) {
        finish();
    }