如何从当前activity再次进入当前activity
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引入：
我在公司负责了一个阅读器上的笔记软件，可以供用户签字，画画，涂鸦，以及再次修改画画的功能，在内部可以新增页面和删除页面等众多操作供用户选择。
/* * Copyright (C) 2007 The Android Open Source Project * Copyright (C) 2011-2014 Freescale Semiconductor, Inc. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */package com.example.handwriting;import android.app.Activity;import android.content.Context;import android.graphics.*;import android.os.Bundle;import android.os.Handler;import android.os.Message;import android.view.Menu;import android.view.MenuItem;import android.view.MotionEvent;import android.view.View;import android.util.Log;import java.util.Timer; import java.util.TimerTask;import java.io.FileDescriptor;import java.io.PrintWriter;import java.util.ArrayDeque;import java.util.Iterator;import java.io.File;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;public class HandWriting extends Activity { private static final int CLEAR_MENU_ID = Menu.FIRST; private static final int SLOW_MENU_ID = Menu.FIRST + 1; private static final int FAST_MENU_ID = Menu.FIRST + 2; private final static String TAG = "HandWriting"; private Paint mPaint; /** The view responsible for drawing the window. */ MyView mView;public static void fast_draw_set(boolean on_off) { try { FileOutputStream fileOutputStream = new FileOutputStream("/proc/epdc_fb/fast_vsync");if (on_off == true)fileOutputStream.write("cinread 1".getBytes());elsefileOutputStream.write("cinread0".getBytes()); fileOutputStream.close(); } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } }/** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Log.w(TAG,"Oncreate =================="); // Create and attach the view that is responsible for painting. mView = new MyView(this); setContentView(mView); mView.requestFocus(); /* TimerTask task = new TimerTask(){ public void run(){ //execute the task mView.postInvalidate(mView.EINK_AUTO_MODE_REGIONAL | mView.EINK_WAIT_MODE_WAIT | mView.EINK_WAVEFORM_MODE_AUTO | mView.EINK_UPDATE_MODE_FULL); //mView.postinvalidate(); }};Timer timer = new Timer();timer.schedule(task, 1000*2); */ } @Overridepublic void onResume() {super.onResume();fast_draw_set(true); //开启高帧率模式，适合画画,手写}@Override public void onPause() {super.onPause();fast_draw_set(false); //关闭高帧率模式} @Override public boolean onCreateOptionsMenu(Menu menu) { super.onCreateOptionsMenu(menu); menu.add(0, CLEAR_MENU_ID, 0, "Clear").setShortcut('3', 'c'); menu.add(0, SLOW_MENU_ID, 0, "Slow").setShortcut('4', 's'); menu.add(0, FAST_MENU_ID, 0, "Fast").setShortcut('5', 'f'); mView.invalidate(mView.EINK_UPDATE_MODE_FULL); return true; } @Override public boolean onPrepareOptionsMenu(Menu menu) { super.onPrepareOptionsMenu(menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { mPaint.setXfermode(null); mPaint.setAlpha(0xFF); switch (item.getItemId()) { case CLEAR_MENU_ID: mView.clear(); return true; case FAST_MENU_ID: mView.setUpdateType(0); return true; case SLOW_MENU_ID: mView.setUpdateType(1); return true; } return super.onOptionsItemSelected(item); } @Override public boolean onTrackballEvent(MotionEvent event) { mView.onTrackballEvent(event); return true; }/* @Override protected void onPause() { mView.onPause(); super.onPause(); } @Override protected void onResume() { mView.onResume(); super.onResume(); }*/ public class MyView extends View { private Bitmap mBitmap; private Canvas mCanvas; private Path mPath; private int mLastX, mLastY; private final Rect mRect = new Rect(); private final Rect mlastRect = new Rect(); boolean mUpdateFlag = false; boolean mStartFlag = false; boolean mFirstPointFlag = true; boolean mNewRegionFlag = true; private int mCurX; private int mCurY; private float mCurSize; private int mCurWidth;private TimerTask mTimerTask = null;private Timer mTimer = null; private int mWidth; private int mHight; private int first = 0; private int mEvent = 0; //0 touch event; 1 trackball private int mUpdateType = 0; //0 fast type; 1 slow type; /** Used as a pulse to gradually fade the contents of the window. */ private static final int UPDATE_MSG = 1; /** How often to fade the contents of the window (in ms). */ private static final int UPDATE_DELAY = 10; /*update mode for handwriting in eink*/private static final int UPDATE_MODE_PARTIAL = EINK_WAIT_MODE_NOWAIT | EINK_WAVEFORM_MODE_ANIM | EINK_UPDATE_MODE_PARTIAL;private static final int UPDATE_MODE_PARTIAL2 = EINK_WAIT_MODE_NOWAIT | EINK_WAVEFORM_MODE_DU |EINK_UPDATE_MODE_PARTIAL;// private static final int UPDATE_MODE_PARTIAL = EINK_AUTO_MODE_REGIONAL| EINK_WAIT_MODE_NOWAIT | EINK_WAVEFORM_MODE_DU | EINK_UPDATE_MODE_PARTIAL; //private static final int UPDATE_MODE_PARTIAL = EINK_WAIT_MODE_NOWAIT | EINK_WAVEFORM_MODE_ANIM; //private static final int UPDATE_MODE_FULL = EINK_AUTO_MODE_REGIONAL| EINK_WAIT_MODE_WAIT | EINK_WAVEFORM_MODE_AUTO | EINK_UPDATE_MODE_FULL; private static final int UPDATE_MODE_FULL = EINK_AUTO_MODE_REGIONAL | EINK_WAIT_MODE_WAIT | EINK_WAVEFORM_MODE_AUTO | EINK_UPDATE_MODE_FULL; public MyView(Context c) { super(c); mPaint = new Paint(); mPaint.setAntiAlias(false); mPaint.setDither(false); mPaint.setColor(0xff000000); mPaint.setStyle(Paint.Style.STROKE); mPaint.setStrokeJoin(Paint.Join.ROUND); mPaint.setStrokeCap(Paint.Cap.ROUND); mPaint.setStrokeWidth(10); mPath = new Path(); mRect.left = 0; mRect.top = 0; mRect.right = 0; mRect.bottom = 0; mlastRect.left = 0; mlastRect.top = 0; mlastRect.right = 0; mlastRect.bottom = 0; mFirstPointFlag = true; mHight = 0; mWidth = 0; } @Override protected void onSizeChanged(int w, int h, int oldw, int oldh) { int curW = mBitmap != null ? mBitmap.getWidth() : 0; int curH = mBitmap != null ? mBitmap.getHeight() : 0; if (curW >= w && curH >= h) { return; } if (curW < w) curW = w; if (curH < h) curH = h; mHight = curH; mWidth = curW; Bitmap newBitmap = Bitmap.createBitmap(curW, curH, Bitmap.Config.ARGB_8888); Canvas newCanvas = new Canvas(); newCanvas.setBitmap(newBitmap); if (mBitmap != null) { newCanvas.drawBitmap(mBitmap, 0, 0, null); } mBitmap = newBitmap; mCanvas = newCanvas; mCanvas.drawColor(0xFFFFFFFF); } @Override protected void onDraw(Canvas canvas) { //super.onDraw(canvas); //canvas.drawPath(mPath, mPaint); canvas.drawBitmap(mBitmap, 0, 0, null); //canvas.drawPath(mPath, mPaint); } public void onPause() { // Override if necessary mBitmap.eraseColor(0xFFFFFFFF); //invalidate(UPDATE_MODE_FULL ); } public void clear() { if (mCanvas != null) {// Log.i(TAG, ("clear() start\n")); mPath.reset(); mBitmap.eraseColor(0xFFFFFFFF); invalidate(UPDATE_MODE_FULL ); mUpdateFlag = false; mRect.left = 0; mRect.top = 0; mRect.right = 0; mRect.bottom = 0; mlastRect.left = 0; mlastRect.top = 0; mlastRect.right = 0; mlastRect.bottom = 0; mEvent =0; mFirstPointFlag = true; mNewRegionFlag = true; } } public void setUpdateType(int type) { switch (type) { case 0: mUpdateType = 0; break; case 1: mUpdateType = 1; break; default: mUpdateType = 0; break; } } public synchronized void update() { if (mCanvas != null) { int left = mRect.left ; int top = mRect.top ; int right = mRect.right ; int bottom = mRect.bottom ; if(left <0) left =0; if(top <0) top =0; if(right <0) right =0; if(bottom <0) bottom =0;/* if(mNewRegionFlag == true) { if( mEvent == 1 ) { //Log.i(TAG, ("end update 1\n")); mUpdateFlag = false; } }else*/ { // Log.i(TAG, ("left=" + left +" top="+ top +" right="+ right+ " bottom="+ bottom +"")); mCanvas.drawPath(mPath, mPaint); invalidate(left, top, right, bottom , EINK_WAIT_MODE_NOWAIT | EINK_WAVEFORM_MODE_DU |EINK_UPDATE_MODE_PARTIAL); mNewRegionFlag = true; } } } /** * Start up the pulse to update the screen, clearing any existing pulse to * ensure that we don't have multiple pulses running at a time. */ void startUpdating() { mStartFlag = true; mUpdateFlag = true; mHandler.removeMessages(UPDATE_MSG); mHandler.sendMessageDelayed(mHandler.obtainMessage(UPDATE_MSG), 0); } /** * Stop the pulse to fade the screen. */ void stopUpdating() { mHandler.removeMessages(UPDATE_MSG); } private Handler mHandler = new Handler() { @Override public void handleMessage(Message msg) { switch (msg.what) { // Upon receiving the update pulse, we have the view perform a // update and then enqueue a new message to pulse at the desired // next time. case UPDATE_MSG: { update(); if(mUpdateFlag == false) { // Log.i(TAG, ("end update 2\n")); stopUpdating(); }else { mHandler.sendMessageDelayed(mHandler.obtainMessage(UPDATE_MSG),0); } break; } default: super.handleMessage(msg); } } }; @Override public boolean onTouchEvent(MotionEvent event) { mEvent = 0; switch (event.getAction()) { case MotionEvent.ACTION_DOWN: startUpdating(); break; case MotionEvent.ACTION_MOVE: break; case MotionEvent.ACTION_UP: mUpdateFlag = false; break; } int N = event.getHistorySize();//Log.i(TAG, "event.getHistorySize" + N ); for (int i=0; i<N; i++) { drawPoint(event.`(i), event.getHistoricalY(i), event.getHistoricalPressure(i), event.getHistoricalSize(i)); } drawPoint(event.getX(), event.getY(), event.getPressure(), event.getSize()); return true; } @Override public boolean onTrackballEvent(MotionEvent event) { mEvent = 1; if(mUpdateFlag == false) { Log.i(TAG, ("start update \n")); startUpdating(); } int N = event.getHistorySize(); int baseX = mCurX; int baseY = mCurY; final float scaleX = event.getXPrecision(); final float scaleY = event.getYPrecision(); for (int i=0; i<N; i++) { drawPoint(baseX+event.getHistoricalX(i)*scaleX, baseY+event.getHistoricalY(i)*scaleY, event.getHistoricalPressure(i), event.getHistoricalSize(i)); update(); } drawPoint(baseX+event.getX()*scaleX, baseY+event.getY()*scaleY, event.getPressure(), event.getSize()); update(); return true; } private synchronized void drawPoint(float x, float y, float pressure, float size) {// Log.i(TAG, ("drawPoint() start \n")); int oldleft = mRect.left ; int oldtop = mRect.top ; int oldright = mRect.right ; int oldbottom = mRect.bottom ; int newleft = 0 ; int newtop = 0 ; int newright = 0 ; int newbottom = 0 ; int targetleft = 0 ; int targettop = 0 ; int targetright = 0 ; int targetbottom = 0 ; mCurX = (int)x; mCurY = (int)y; if(mCurY > mHight) mCurY = mHight; if(mCurY < 0 ) mCurY = 0; if(mCurX > mWidth) mCurX = mWidth; if(mCurX < 0 ) mCurX = 0; mCurSize = size; mCurWidth = (int)(mCurSize*(getWidth()/3)); if (mCurWidth < 1) mCurWidth = 1; if ( mCanvas != null) { newleft = mCurX-mCurWidth-2; newtop = mCurY-mCurWidth-2; newright = mCurX+mCurWidth+2; newbottom = mCurY+mCurWidth+2; if(mFirstPointFlag == true) { mFirstPointFlag=false; oldleft = newleft; oldtop = newtop ; oldright = newright; oldbottom = newbottom; mPath.reset(); mPath.moveTo(mCurX, mCurY); mNewRegionFlag = false; }else { if(mNewRegionFlag==true) { if( mStartFlag== true && mEvent== 0) { mStartFlag = false; oldleft = newleft; oldtop = newtop ; oldright = newright; oldbottom = newbottom; mPath.reset(); mPath.moveTo(mCurX, mCurY); } else { oldleft = mlastRect.left; oldtop = mlastRect.top ; oldright = mlastRect.right; oldbottom = mlastRect.bottom; } mNewRegionFlag = false; } } mlastRect.left = newleft; mlastRect.top = newtop; mlastRect.right = newright; mlastRect.bottom = newbottom; { mPath.lineTo(mCurX, mCurY); if(oldleft < newleft) targetleft = oldleft; else targetleft = newleft; if(oldtop < newtop) targettop = oldtop; else targettop = newtop; if(oldright < newright) targetright = newright; else targetright = oldright; if(oldbottom < newbottom) targetbottom = newbottom; else targetbottom = oldbottom; } mRect.set(targetleft, targettop, targetright, targetbottom); }// Log.i(TAG, ("drawPoint() end \n")); } }}新建页面我只是做了保存当前页面，清空画布的逻辑，但是addNote后，笔记画的速度变慢了，然后我在MyView中的Handler机制中打印日志，输出的日志前后两次相比较，有差不多一倍之差，（我的上上篇有截图）但是总时长是对的，所以我开始想从Handler这里出发去解决他，后来问了好多人，也包括查各种stackoverflow论坛寻求答案；只有下面一些作参考
1.handler机制有可能随着CPU的荷载而变化
2.跟死循环一样
3.addNote后经可能的释放掉一些资源
然后想了半天，最后觉得应该是跟资源有关，用DDMS和AS分析了一下CPU和内存，然后便想到了试试结束当前activity，从而释放更多的资源，让下次绘制的时候又是最初的状态，而能够恢复其原有的速度呢？
开始在网上搜索activity的自我reset，结果不出所料，被我找到了。
public static void restartActivity(Activity act){ Intent intent=new Intent(); intent.setClass(act, act.getClass()); act.startActivity(intent); act.finish();}我也做了一些扩展，比如传过来的path和name什么的，以及type区分是否是新建空白的等等，然后增加2个变量，一个position用来控制页码，一个boolean值用来控制删除。。。。。。。。。。。
最后解决了，速度跟之前的一样快，两次日志一样，帧率上来了
写下来，记录一下，以后留作纪念
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