Snake作爲Android源碼中的遊戲，是很經典的。通過對代碼的閱讀，我瞭解了Handler相關的處理功能、Drawable繪製、以及遊戲的基本流程，遊戲邏輯的處理。
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以下代碼是在參閱別人博客的，註釋懶得寫，看到別人註釋好的直接拿來用了。自己寫的很少。主要是作爲學習用的，希望各位博主諒解。
TileView類作爲SnakeView類的父類，負責基本的圖片顯示處理。將屏幕分成若干個圖像點（即切片），然後根據 每個圖像點的值（mTileGrid【x】【y】的值,x,y代表其物理位置，mTileGrid【x】【y】爲相應的值，比如紅、黃、藍分別爲1,2,3）對其進行顯示。
/*
* Copyright (C) 2007 The Android Open Source Project
*
* 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.android.snake;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.view.View;
/**
* TileView: a View-variant designed for handling arrays of "icons" or other
* drawables.
*
* View變種，用來處理一組貼片--icons或者其他可繪製對象
*/
public class TileView extends View {
/**
* Parameters controlling the size of the tiles and their range within view.
* Width/Height are in pixels, and Drawables will be scaled to fit to these
* dimensions. X/Y Tile Counts are the number of tiles that will be drawn.
*/
//切片大小
protected static int mTileSize;
//x軸的貼片數量
protected static int mXTileCount;
//y軸的貼片數量
protected static int mYTileCount;
//Offset這裏做偏移量解釋並不合適，應該是初始原點，以後的點都參考改點進行移動
private static int mXOffset;
private static int mYOffset;
/**
* A hash that maps integer handles specified by the subclasser to the
* drawable that will be used for that reference
*/
private Bitmap[] mTileArray;
/**
* A two-dimensional array of integers in which the number represents the
* index of the tile that should be drawn at that locations
*/
private int[][] mTileGrid;
private final Paint mPaint = new Paint();
public TileView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.TileView);
mTileSize = a.getInt(R.styleable.TileView_tileSize, 12);
a.recycle();
}
public TileView(Context context, AttributeSet attrs) {
super(context, attrs);
TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.TileView);
mTileSize = a.getInt(R.styleable.TileView_tileSize, 12);
a.recycle();
}
/**
* Rests the internal array of Bitmaps used for drawing tiles, and
* sets the maximum index of tiles to be inserted
*
* @param tilecount
*/
public void resetTiles(int tilecount) {
mTileArray = new Bitmap[tilecount];
}
//在View第一次加載時會首先調用onSizeChanged，這裏就是做這些事的最好時機
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
//計算屏幕中可放置的方格的行數和列數
//注意模擬器屏幕默認的像素是320×400，而代碼中默認的方格大小爲12，
//因此屏幕上放置的方格數爲26×40，把屏幕剖分成這麼大後，再設置一個相應的二維int型數組來記錄每一個方格的狀態，
//根據方格的狀態，可以從mTileArray保存的圖標文件中讀取對應的狀態圖標。
mXTileCount = (int) Math.floor(w / mTileSize);
mYTileCount = (int) Math.floor(h / mTileSize);
//mXOffset mYOffset是繪圖的起點座標。
mXOffset = ((w - (mTileSize * mXTileCount)) / 2);
mYOffset = ((h - (mTileSize * mYTileCount)) / 2);
mTileGrid = new int[mXTileCount][mYTileCount];
clearTiles();
}
/**
* Function to set the specified Drawable as the tile for a particular
* integer key.
*
* 即將對應的磚塊的圖片 對應的加載到 mTileArray數組中
*
* @param key
* @param tile
*/
public void loadTile(int key, Drawable tile) {
//這裏做了一個 Drawable 到 bitmap 的轉換。由於外部程序使用的時候是直接讀取資源文件中的圖片，
//是drawable格式，而我們的數組是bitmap格式，方便最終的繪製。所以，需要進行一次到 bitmap的轉換。
Bitmap bitmap = Bitmap.createBitmap(mTileSize, mTileSize, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
tile.setBounds(0, 0, mTileSize, mTileSize);
tile.draw(canvas);
mTileArray[key] = bitmap;
}
/**
* Resets all tiles to 0 (empty)
*
*/
public void clearTiles() {
for (int x = 0; x < mXTileCount; x++) {
for (int y = 0; y < mYTileCount; y++) {
setTile(0, x, y);
}
}
}
/**
* Used to indicate that a particular tile (set with loadTile and referenced
* by an integer) should be drawn at the given x/y coordinates during the
* next invalidate/draw cycle.
*
* @param tileindex
* @param x
* @param y
*/
public void setTile(int tileindex, int x, int y) {
mTileGrid[x][y] = tileindex;
}
//第一次調用完onSizeChanged後，會緊跟着第一次來調用onDraw來繪製View自身，
//當然，此時由於所有方格的狀態都是0，所以它在屏幕上等於什麼也不會去繪製。
@Override
public void onDraw(Canvas canvas) {
super.onDraw(canvas);
for (int x = 0; x < mXTileCount; x += 1) {
for (int y = 0; y < mYTileCount; y += 1) {
if (mTileGrid[x][y] > 0) {
canvas.drawBitmap(mTileArray[mTileGrid[x][y]],
mXOffset + x * mTileSize,
mYOffset + y * mTileSize,
mPaint);
}
}
}
}
}
SnakeView類主要負責遊戲邏輯控制，利用RefreshHandler類（繼承了Handler類）對遊戲狀態進行檢測並不斷刷新，從而驅動遊戲運行。
SnakeView類代碼如下：
/*
* Copyright (C) 2007 The Android Open Source Project
*
* 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.android.snake;
import java.util.ArrayList;
import java.util.Random;
import android.content.Context;
import android.content.res.Resources;
import android.os.Handler;
import android.os.Message;
import android.util.AttributeSet;
import android.os.Bundle;
import android.util.Log;
import android.view.KeyEvent;
import android.view.View;
import android.widget.TextView;
/**
* SnakeView: implementation of a simple game of Snake
*
*
*/
public class SnakeView extends TileView {
private static final String TAG = "SnakeView";
/**
* Current mode of application: READY to run, RUNNING, or you have already
* lost. static final ints are used instead of an enum for performance
* reasons.
*/
private int mMode = READY;
public static final int PAUSE = 0;
public static final int READY = 1;
public static final int RUNNING = 2;
public static final int LOSE = 3;
/**
* Current direction the snake is headed.
*/
private int mDirection = NORTH;
private int mNextDirection = NORTH;
private static final int NORTH = 1;
private static final int SOUTH = 2;
private static final int EAST = 3;
private static final int WEST = 4;
/**
* Labels for the drawables that will be loaded into the TileView class
*/
private static final int RED_STAR = 1;
private static final int YELLOW_STAR = 2;
private static final int GREEN_STAR = 3;
/**
* mScore: used to track the number of apples captured mMoveDelay: number of
* milliseconds between snake movements. This will decrease as apples are
* captured.
*/
private long mScore = 0;
private long mMoveDelay = 600;
/**
* mLastMove: tracks the absolute time when the snake last moved, and is used
* to determine if a move should be made based on mMoveDelay.
*/
private long mLastMove;
/**
* mStatusText: text shows to the user in some run states
*/
private TextView mStatusText;
/**
* mSnakeTrail: a list of Coordinates that make up the snake's body
* mAppleList: the secret location of the juicy apples the snake craves.
*/
private ArrayList<Coordinate> mSnakeTrail = new ArrayList<Coordinate>();
private ArrayList<Coordinate> mAppleList = new ArrayList<Coordinate>();
/**
* Everyone needs a little randomness in their life
*/
private static final Random RNG = new Random();
/**
* Create a simple handler that we can use to cause animation to happen. We
* set ourselves as a target and we can use the sleep()
* function to cause an update/invalidate to occur at a later date.
*/
private RefreshHandler mRedrawHandler = new RefreshHandler();
class RefreshHandler extends Handler {
//響應消息,獲取消息並處理
@Override
public void handleMessage(Message msg) {
SnakeView.this.update();
SnakeView.this.invalidate();
}
// 向外提供人工的調用消息的接口
//定時發送消息給UI線程，以此達到更新的效果。
public void sleep(long delayMillis) {
//註銷消息
this.removeMessages(0);//清空消息隊列，Handler進入對新消息的等待
//添加消息
sendMessageDelayed(obtainMessage(0), delayMillis);//定時發送新消息,激活handler
}
};
/**
* Constructs a SnakeView based on inflation from XML
*
* @param context
* @param attrs
*/
public SnakeView(Context context, AttributeSet attrs) {
super(context, attrs);
initSnakeView();
}
public SnakeView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
initSnakeView();
}
private void initSnakeView() {
setFocusable(true);//設置焦點，由於存在 文字界面 和 遊戲界面的跳轉。這個focus是不可或缺的。
Resources r = this.getContext().getResources();
resetTiles(4);
loadTile(RED_STAR, r.getDrawable(R.drawable.redstar));
loadTile(YELLOW_STAR, r.getDrawable(R.drawable.yellowstar));
loadTile(GREEN_STAR, r.getDrawable(R.drawable.greenstar));
}
private void initNewGame() {
mSnakeTrail.clear();
mAppleList.clear();
// For now we're just going to load up a short default eastbound snake
// that's just turned north
mSnakeTrail.add(new Coordinate(7, 7));
mSnakeTrail.add(new Coordinate(6, 7));
mSnakeTrail.add(new Coordinate(5, 7));
mSnakeTrail.add(new Coordinate(4, 7));
mSnakeTrail.add(new Coordinate(3, 7));
mSnakeTrail.add(new Coordinate(2, 7));
mNextDirection = NORTH;
// Two apples to start with
addRandomApple();
addRandomApple();
mMoveDelay = 600;
mScore = 0;
}
/**
* Given a ArrayList of coordinates, we need to flatten them into an array of
* ints before we can stuff them into a map for flattening and storage.
*
* @param cvec : a ArrayList of Coordinate objects
* @return : a simple array containing the x/y values of the coordinates
* as [x1,y1,x2,y2,x3,y3...]
*
* 在遊戲暫停時，需要通過Bundle方式保存數據。見saveState()。
* Bundle支持簡單的數組。
* 所以需要將我們的部分數據結構，如蛇體和蘋果位置的數組，轉換成簡單的序列化的int數組。
*/
private int[] coordArrayListToArray(ArrayList<Coordinate> cvec) {
int count = cvec.size();
int[] rawArray = new int[count * 2];
for (int index = 0; index < count; index++) {
Coordinate c = cvec.get(index);
rawArray[2 * index] = c.x;
rawArray[2 * index + 1] = c.y;
}
return rawArray;
}
/**
* Save game state so that the user does not lose anything
* if the game process is killed while we are in the
* background.
*
* @return a Bundle with this view's state
*/
public Bundle saveState() {
//Bundle:A mapping from String values to various Parcelable types.
Bundle map = new Bundle();
map.putIntArray("mAppleList", coordArrayListToArray(mAppleList));
map.putInt("mDirection", Integer.valueOf(mDirection));
map.putInt("mNextDirection", Integer.valueOf(mNextDirection));
map.putLong("mMoveDelay", Long.valueOf(mMoveDelay));
map.putLong("mScore", Long.valueOf(mScore));
map.putIntArray("mSnakeTrail", coordArrayListToArray(mSnakeTrail));
return map;
}
/**
* Given a flattened array of ordinate pairs, we reconstitute them into a
* ArrayList of Coordinate objects
*
* @param rawArray : [x1,y1,x2,y2,...]
* @return a ArrayList of Coordinates
*/
private ArrayList<Coordinate> coordArrayToArrayList(int[] rawArray) {
ArrayList<Coordinate> coordArrayList = new ArrayList<Coordinate>();
int coordCount = rawArray.length;
for (int index = 0; index < coordCount; index += 2) {
Coordinate c = new Coordinate(rawArray[index], rawArray[index + 1]);
coordArrayList.add(c);
}
return coordArrayList;
}
/**
* Restore game state if our process is being relaunched
* 恢復遊戲數據
* @param icicle a Bundle containing the game state
*/
public void restoreState(Bundle icicle) {
setMode(PAUSE);
mAppleList = coordArrayToArrayList(icicle.getIntArray("mAppleList"));
mDirection = icicle.getInt("mDirection");
mNextDirection = icicle.getInt("mNextDirection");
mMoveDelay = icicle.getLong("mMoveDelay");
mScore = icicle.getLong("mScore");
mSnakeTrail = coordArrayToArrayList(icicle.getIntArray("mSnakeTrail"));
}
/*
* handles key events in the game. Update the direction our snake is traveling
* based on the DPAD. Ignore events that would cause the snake to immediately
* turn back on itself.
*
* (non-Javadoc)
*
* @see android.view.View#onKeyDown(int, android.os.KeyEvent)
*/
@Override
public boolean onKeyDown(int keyCode, KeyEvent msg) {
if (keyCode == KeyEvent.KEYCODE_DPAD_UP) {
if (mMode == READY | mMode == LOSE) {
/*
* At the beginning of the game, or the end of a previous one,
* we should start a new game.
*/
initNewGame();
setMode(RUNNING);
update();
return (true);
}
if (mMode == PAUSE) {
/*
* If the game is merely paused, we should just continue where
* we left off.
*/
setMode(RUNNING);
update();
return (true);
}
if (mDirection != SOUTH) {
mNextDirection = NORTH;
}
return (true);
}
if (keyCode == KeyEvent.KEYCODE_DPAD_DOWN) {
if (mDirection != NORTH) {
mNextDirection = SOUTH;
}
return (true);
}
if (keyCode == KeyEvent.KEYCODE_DPAD_LEFT) {
if (mDirection != EAST) {
mNextDirection = WEST;
}
return (true);
}
if (keyCode == KeyEvent.KEYCODE_DPAD_RIGHT) {
if (mDirection != WEST) {
mNextDirection = EAST;
}
return (true);
}
return super.onKeyDown(keyCode, msg);
}
/**
* Sets the TextView that will be used to give information (such as "Game
* Over" to the user.
*
* @param newView
*/
public void setTextView(TextView newView) {
mStatusText = newView;
}
/**
* Updates the current mode of the application (RUNNING or PAUSED or the like)
* as well as sets the visibility of textview for notification
*
* @param newMode
*/
public void setMode(int newMode) {
int oldMode = mMode;
mMode = newMode;
if (newMode == RUNNING & oldMode != RUNNING) {//???這個地方&和&&作用應該是一樣的，因爲其只有一位
mStatusText.setVisibility(View.INVISIBLE);
update();//注意到，在initGame中也有update(),不過放心～ 多次重複 update不會影響效果的，
//蛇的移動有mLastMove 和 mMoveDelay 來校驗。這會在Update()中體現。
//當然，經過實驗，註釋掉這個update()似乎不會影響結果噢。
return;
}
Resources res = getContext().getResources();
CharSequence str = "";
if (newMode == PAUSE) {
str = res.getText(R.string.mode_pause);
}
if (newMode == READY) {
str = res.getText(R.string.mode_ready);
}
if (newMode == LOSE) {
str = res.getString(R.string.mode_lose_prefix) + mScore
+ res.getString(R.string.mode_lose_suffix);
}
mStatusText.setText(str);
mStatusText.setVisibility(View.VISIBLE);
}
/**
* Selects a random location within the garden that is not currently covered
* by the snake. Currently _could_ go into an infinite loop if the snake
* currently fills the garden, but we'll leave discovery of this prize to a
* truly excellent snake-player.
*
* 在地圖上隨機的增加果子。注意蘋果的位置不可以是蛇體所在噢～這裏有個小bug，沒有檢測
* 產生的果子位置 可能與 另一個果子位置重合。
* 新產生的果子的座標會增加到mApplist的數組上。
*
*/
private void addRandomApple() {
Coordinate newCoord = null;
boolean found = false;
while (!found) {
// Choose a new location for our apple
int newX = 1 + RNG.nextInt(mXTileCount - 2);
int newY = 1 + RNG.nextInt(mYTileCount - 2);
newCoord = new Coordinate(newX, newY);
// Make sure it's not already under the snake
boolean collision = false;
int snakelength = mSnakeTrail.size();
for (int index = 0; index < snakelength; index++) {
if (mSnakeTrail.get(index).equals(newCoord)) {
collision = true;
break;//經過測驗，如果已經檢測到衝突，這裏是可以添加break提前結束循環的
}
}
// if we're here and there's been no collision, then we have
// a good location for an apple. Otherwise, we'll circle back
// and try again
found = !collision;
}
if (newCoord == null) {
Log.e(TAG, "Somehow ended up with a null newCoord!");
}
mAppleList.add(newCoord);
}
/**
* Handles the basic update loop, checking to see if we are in the running
* state, determining if a move should be made, updating the snake's location.
*/
public void update() {
if (mMode == RUNNING) {
long now = System.currentTimeMillis();
if (now - mLastMove > mMoveDelay) {
clearTiles();
updateWalls();
updateSnake();
updateApples();
mLastMove = now;
}
mRedrawHandler.sleep(mMoveDelay);
}
}
/**
* Draws some walls.
*
*/
private void updateWalls() {
for (int x = 0; x < mXTileCount; x++) {
setTile(GREEN_STAR, x, 0);
setTile(GREEN_STAR, x, mYTileCount - 1);
}
for (int y = 1; y < mYTileCount - 1; y++) {
setTile(GREEN_STAR, 0, y);
setTile(GREEN_STAR, mXTileCount - 1, y);
}
}
/**
* Draws some apples.
*
*/
private void updateApples() {
for (Coordinate c : mAppleList) {
setTile(YELLOW_STAR, c.x, c.y);
}
}
/**
* * 設置當前蛇的方向位置：
* 從以上的鍵盤代碼我們可以看得出，程序中是通過觸發來改變座標（+1，-1）的方式來改蛇頭的方向，
* 可見座標在遊戲編程中的作用， 這個也是根據手機的屏幕是點陣的方式來顯示， 所以座標就是一個
* 定位器。 在這裏大家可能還有一個疑問。 就是就這個蛇什麼能夠以“7”字形來移動行走， 其實我們
* 稍微仔細觀察一下就知道了，在這裏面， 他們也是通過座標的傳遞來實現的， 只要把頭部的座標點
* 依次賦給下一個點， 後面的每一個點都走過了頭部所走過的點，而蛇的頭部就是負責去獲取座標，整
* 個蛇的行走起來就很自然和連貫。 座標的方向變換又是通過判斷那個方向按鍵的按下來改變的， 這
* 樣一來， 鍵盤的作用就發揮出來了。蛇喫蘋果又是怎樣去實現？上面我所說到的座標就起了作用。在蛇
* 所經過的每一個座標， 他們都要在蘋果所在的（ArrayList<Coordinate> mAppleList = new
* ArrayList<Coordinate>()）座標集裏面集依次判斷，若是座標相同，那個這個蘋果就被蛇吃了 。
*
* Figure out which way the snake is going, see if he's run into anything (the
* walls, himself, or an apple). If he's not going to die, we then add to the
* front and subtract from the rear in order to simulate motion. If we want to
* grow him, we don't subtract from the rear.
*
*/
private void updateSnake() {
boolean growSnake = false;
// grab the snake by the head
Coordinate head = mSnakeTrail.get(0);
Coordinate newHead = new Coordinate(1, 1);
mDirection = mNextDirection;
switch (mDirection) {
case EAST: {
newHead = new Coordinate(head.x + 1, head.y);
break;
}
case WEST: {
newHead = new Coordinate(head.x - 1, head.y);
break;
}
case NORTH: {
newHead = new Coordinate(head.x, head.y - 1);
break;
}
case SOUTH: {
newHead = new Coordinate(head.x, head.y + 1);
break;
}
}
// Collision detection
// For now we have a 1-square wall around the entire arena
if ((newHead.x < 1) || (newHead.y < 1) || (newHead.x > mXTileCount - 2)
|| (newHead.y > mYTileCount - 2)) {
setMode(LOSE);
return;
}
// Look for collisions with itself
int snakelength = mSnakeTrail.size();
for (int snakeindex = 0; snakeindex < snakelength; snakeindex++) {
Coordinate c = mSnakeTrail.get(snakeindex);
if (c.equals(newHead)) {
setMode(LOSE);
return;
}
}
// Look for apples
int applecount = mAppleList.size();
for (int appleindex = 0; appleindex < applecount; appleindex++) {
Coordinate c = mAppleList.get(appleindex);
if (c.equals(newHead)) {
mAppleList.remove(c);
addRandomApple();
mScore++;
mMoveDelay *= 0.9;
growSnake = true;
}
}
// push a new head onto the ArrayList and pull off the tail
mSnakeTrail.add(0, newHead);
// except if we want the snake to grow
if (!growSnake) {
mSnakeTrail.remove(mSnakeTrail.size() - 1);
}
int index = 0;
for (Coordinate c : mSnakeTrail) {
if (index == 0) {
setTile(YELLOW_STAR, c.x, c.y);
} else {
setTile(RED_STAR, c.x, c.y);
}
index++;
}
}
/**
* Simple class containing two integer values and a comparison function.
* There's probably something I should use instead, but this was quick and
* easy to build.
*
*/
private class Coordinate {
public int x;
public int y;
public Coordinate(int newX, int newY) {
x = newX;
y = newY;
}
public boolean equals(Coordinate other) {
if (x == other.x && y == other.y) {
return true;
}
return false;
}
@Override
public String toString() {
return "Coordinate: [" + x + "," + y + "]";
}
}
}
參考文章：