我正在尝试在android中学习游戏开发。首先，我尝试每五秒钟使用游戏循环在屏幕上出现和消失一个对象。但我没有成功。我读过不同的教程和论坛。我像教程中一样应用了所有的东西，但对象仍然在不断地绘制。它并没有消失。我没有得到我所缺少的？请引导我。
完整的代码在这里：
MainGameActivity.java
package com.example.showandhideobject;
import android.app.Activity;
import android.os.Bundle;
import android.view.Window;
import android.view.WindowManager;
public class MainGameActivity extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
setContentView(new MainGamePanel(this));
}
}
MainGamePanel.java
package com.example.showandhideobject;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
public class MainGamePanel extends SurfaceView implements
SurfaceHolder.Callback {
private MainGameThread thread;
private ImageObject image;
// private long gameStartTime;
public MainGamePanel(Context context) {
super(context);
// adding the callback (this) to the surface holder to intercept events
getHolder().addCallback(this);
// create the game loop thread
thread = new MainGameThread(getHolder(), this);
Bitmap imageBitMap = BitmapFactory.decodeResource(getResources(),
R.drawable.rose);
image = new ImageObject(imageBitMap, 100, 150);
image.setAppeared(false);
image.setDisappearTime(System.currentTimeMillis());
// make the GamePanel focusable so it can handle events
setFocusable(true);
}
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width,
int height) {
}
@Override
public void surfaceCreated(SurfaceHolder holder) {
// at this point the surface is created and
// we can safely start the game loop
thread.setRunning(true);
thread.start();
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
}
public void update() {
Log.i("Image Status::::::::::::: ",
Boolean.valueOf(image.isAppeared()).toString());
if (!image.isAppeared()
&& System.currentTimeMillis() - image.getDisappearTime() >= 5000) {
Log.i("Image Object::::::: ", "Showing");
image.setAppeared(true);
image.setAppearTime(System.currentTimeMillis());
}
if (image.isAppeared()
&& (System.currentTimeMillis() - image.getAppearTime() >= 5000)) {
Log.i("Image Object::::::: ", "Not Showing");
image.setAppeared(false);
image.setDisappearTime(System.currentTimeMillis());
}
}
public void render(Canvas canvas) {
if (image.isAppeared()) {
image.draw(canvas);
}
}
}
MainGameThread.java
package com.example.showandhideobject;
import android.graphics.Canvas;
import android.util.Log;
import android.view.SurfaceHolder;
public class MainGameThread extends Thread {
// Surface holder that can access the physical surface
private SurfaceHolder surfaceHolder;
// The actual view that handles inputs
// and draws to the surface
private MainGamePanel gamePanel;
// flag to hold game state
private boolean running;
public boolean isRunning() {
return running;
}
public void setRunning(boolean running) {
this.running = running;
}
public MainGameThread(SurfaceHolder surfaceHolder, MainGamePanel gamePanel) {
super();
this.surfaceHolder = surfaceHolder;
this.gamePanel = gamePanel;
}
@Override
public void run() {
Canvas canvas;
while (isRunning()) {
canvas = null;
// try locking the canvas for exclusive pixel editing
// in the surface
try {
canvas = this.surfaceHolder.lockCanvas();
synchronized (surfaceHolder) {
Log.i("With in :::::::::", "Game Loop");
// update game state
gamePanel.update();
// render state to the screen and draw the canvas on the
// panel
gamePanel.render(canvas);
// gamePanel.onDraw(canvas);
}
} finally {
// in case of an exception the surface is not left in an
// inconsistent state
if (canvas != null) {
surfaceHolder.unlockCanvasAndPost(canvas);
}
} // end finally
}
}
}
ImageObject.java
package com.example.showandhideobject;
import android.graphics.Bitmap;
import android.graphics.Canvas;
public class ImageObject {
private Bitmap bitmap; // the actual bitmap
private int x; // the X coordinate
private int y; // the Y coordinate
private boolean isAppeared;
private long appearTime;
private long disappearTime;
// Constructor for this class
public ImageObject(Bitmap bitmap, int x, int y) {
this.bitmap = bitmap;
this.x = x;
this.y = y;
}
public Bitmap getBitmap() {
return bitmap;
}
public void setBitmap(Bitmap bitmap) {
this.bitmap = bitmap;
}
public int getX() {
return x;
}
public void setX(int x) {
this.x = x;
}
public int getY() {
return y;
}
public void setY(int y) {
this.y = y;
}
public boolean isAppeared() {
return isAppeared;
}
public void setAppeared(boolean isAppeared) {
this.isAppeared = isAppeared;
}
public long getAppearTime() {
return appearTime;
}
public void setAppearTime(long appearTime) {
this.appearTime = appearTime;
}
public long getDisappearTime() {
return disappearTime;
}
public void setDisappearTime(long disappearTime) {
this.disappearTime = disappearTime;
}
/* Method to draw images on Canvas */
public void draw(Canvas canvas) {
canvas.drawBitmap(bitmap, x - (bitmap.getWidth() / 2),
y - (bitmap.getHeight() / 2), null);
}
}
在本部分
if (image.isAppeared()) {
image.draw(canvas);
}
你从不清理画布。你所做的实际上是在同一个地方一遍又一遍地绘制你的图像。
您可能需要在cas中重新绘制背景isAppeared()是false
编辑
您也可以在绘制图像之前使用canvas.save（），在不需要图像时使用canvas.restore（）。
不要过早地进行优化，游戏渲染通常效率低下，因为屏幕的大部分内容几乎总是会发生变化。
回路应为：
- 始终将背景绘制到画布
- 始终将所有游戏对象绘制到画布上，让它们决定它们是否可见，这将简化MainGamePanel类
- 最后始终显示画布（通过在执行操作时复制到图像）
扩展到第2点：
/* Method to draw images on Canvas */
public void draw(Canvas canvas) {
if(!isAppeared) return; //let the object decide when it should be drawn
canvas.drawBitmap(bitmap, x - (bitmap.getWidth() / 2),
y - (bitmap.getHeight() / 2), null);
}
将MainGamePanel.java中的方法渲染更改为
if (image.isAppeared() && canvas != null) {
image.draw(canvas);
}