Implement dual-buffering (canvas application) and XML file definition menus in Android

1. What is double buffering technology? The dual-buffer technology means that after the user operation interface is complete, a buffer zone will be provided to save the user operation results. Why is dual-buffer technology used? For Android game development, the UI is all re-painted every time, so it is said that there is a new image, and the old one is gone, so we need to use the dual-buffer technology to save the previous content. How to implement dual buffering? Use a Bitmap object to retain the previous canvas. View Source code printing? 01 package com. example. phonegaptest; 02 03 import android. content. context; 04 import android. graphics. bitmap; 05 import android. graphics. bitmap. config; 06 import android. graphics. canvas; 07 import android. graphics. color; 08 import android. graphics. paint; 09 import android. graphics. path; 10 import android. util. attributeSet; 11 import android. view. motionEvent; 12 import android. view. view; 13 14 public class DrawView extend S View {15 float preX; 16 float preY; 17 private Path path; 18 public Paint paint = null; 19 final int VIEW_WIDTH = 320; 20 final int VIEW_HEIGHT = 480; 21 Bitmap cacheBitmap = null; // defines an image in the memory. This image is used as the buffer zone 22 Canvas cacheCanvas = null; // defines the Canvas cacheCanvas23 24 public DrawView (Context context Context, attributeSet) {25 super (context, set); 26 cacheBitmap = Bitmap. createBitmap (VIEW_WIDTH, VIEW_HEIGHT, 27 Config. ARGB_8888); // create the buffer 28 cacheCanvas = new Canvas (); 29 30 path = new Path (); 31 cacheCanvas. setBitmap (cacheBitmap); 32 33 paint = new Paint (Paint. DITHER_FLAG); 34 paint. setColor (Color. RED); 35 paint. setStyle (Paint. style. STROKE); 36 paint. setStrokeWidth (1); 37 paint. setAntiAlias (true); 38 paint. setDither (true); 39} 40 41 @ Override42 public boolean onTouchEvent (MotionEvent event) {43 float x = event. g EtX (); 44 float y = event. getY (); 45 46 switch (event. getAction () {47 case MotionEvent. ACTION_DOWN: 48 path. moveTo (x, y); 49 preX = x; 50 preY = y; 51 break; 52 case MotionEvent. ACTION_MOVE: 53 path. quadTo (preX, preY, x, y); 54 preX = x; 55 preY = y; 56 break; 57 case MotionEvent. ACTION_UP: 58 cacheCanvas. drawPath (path, paint); 59 path. reset (); 60 break; 61} 62 invalidate (); 63 return true; // return true indicates that the processing method has handled the event. Event will not spread 64} 65 66 @ Override67 protected void onDraw (Canvas canvas) {68 super. onDraw (canvas); 69 Paint BMP Paint = new Paint (); 70 canvas. drawBitmap (cacheBitmap, 0, 0, BMP paint); 71 canvas. drawPath (path, paint); 72} 73 74} 2. XMl file implementation menu function XMl file: [html] view plaincopy <? Xml version = "1.0" encoding = "UTF-8"?> <Menu xmlns: android = "http://schemas.android.com/apk/res/android"> <item android: id = "@ + id/close" android: icon = "@ drawable/ic_launcher" android: orderInCategory = "3" android: title = "Close"/> <item android: id = "@ + id/no_icon" android: orderInCategory = "2" android: title = "Sans Icon"/> <item android: id = "@ + id/disabled" android: enabled = "true" android: orderInCategory = "4" android: title = "Disabled"/> <! -- OrderInCategory indicates the sorting of items --> <group android: id = "@ + id/other_stuff" android: menuCategory = "secondary" android: visible = "true"> <item android: id = "@ + id/later" android: orderInCategory = "0" android: title = "2nd-To-Last"/> <item android: id = "@ + id/last" android: orderInCategory = "1" android: title = "Last"/> </group> <! -- Indicates the level-2 menu --> <item android: id = "@ + id/submenu" android: orderInCategory = "3" android: title = "A Submenu"> <menu> <item android: id = "@ + id/non_ghost" android: alphabeticShortcut = "n" android: title = "Non-Ghost" android: visible = "true"/> <item android: id = "@ + id/ghost" android: alphabeticShortcut = "g" android: title = "A Ghost" android: visible = "true"/> </menu> </item> </menu> main file [java] view plaincopypackage com. example. receiveractivity; import android. app. activity; import android. OS. bundle; import android. util. log; import android. view. menu; import android. view. menuInflater; import android. view. menuItem; public class ReceiverActivity extends Activity {/** Called when the activity is first created. */private static final String TAG = "BruceZhang"; @ Override public void onCreate (Bundle savedInstanceState) {super. onCreate (savedInstanceState); setContentView (R. layout. activity_cycler) ;}@ Override public boolean onCreateOptionsMenu (Menu menu) {// TODO Auto-generated method stub MenuInflater mflater = new MenuInflater (this); mflater. inflate (R. menu. activity_receiver, menu); return super. onCreateOptionsMenu (menu) ;}@ Override public boolean onOptionsItemSelected (MenuItem item) {// TODO Auto-generated method stub switch (item. getItemId () {case R. id. close: Log. v (TAG, "------------ close"); break; case R. id. no_icon: Log. v (TAG, "------------ noicon"); break; case R. id. submenu: Log. v (TAG, "------------ submenu"); break; case R. id. non_ghost: Log. v (TAG, "------------ non_ghost"); break; case R. id. ghost: Log. v (TAG, "------------ ghost"); break; case R. id. disabled: Log. v (TAG, "------------ disabled"); break; case R. id. last: Log. v (TAG, "------------ last"); break; www.2cto.com case R. id. later: Log. v (TAG, "------------ laster"); break; default: break;} return super. onOptionsItemSelected (item );}}