编辑:我看了一下 LogCat，它说它不能膨胀 com.example.playground。然后我意识到它需要我 com.game.myapp.Playground。我更改后它起作用了。
我最近问为什么重力在我的 Android 应用程序 (link) 中不起作用，但我仍然遇到问题。我将 View 更改为“ Playground ”类，但现在它只是强制关闭。我究竟做错了什么？
package com.game.myapp;
import android.app.Activity;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.os.Bundle;
public class InGame extends Activity{
Playground v;
private int radius;
private int xPosition;
private int yPosition;
private Paint paint;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Rewrite this, it sucks. Seriously.
super.onCreate(savedInstanceState);
v = new Playground(this);
setContentView(v);
}
public InGame(int x, int y, int radius, int color)
{
this.xPosition = x; this.yPosition = y; this.radius = radius;
paint = new Paint(color);
}
void moveBall(int x, int y){
xPosition = x; yPosition =y;
}
void onDraw(Canvas canvas){
canvas.drawCircle(xPosition, yPosition, radius, paint);
}
}
Playground 类:
package com.game.myapp;
import android.content.Context;
import android.graphics.Canvas;
import android.view.View;
public class Playground extends View{
public static InGame ball;
public Playground(Context context) {
super(context);
// TODO Auto-generated constructor stub
}
@Override
public void onDraw(Canvas canvas)
{
super.onDraw(canvas);
if (ball != null ){
ball.onDraw(canvas);
}
}
}
这是 LogCat:
11-04 16:36:33.945: D/dalvikvm(13177): newInstance failed: no <init>()
11-04 16:36:33.949: D/AndroidRuntime(13177): Shutting down VM
11-04 16:36:33.949: W/dalvikvm(13177): threadid=1: thread exiting with uncaught exception (group=0x4001e578)
11-04 16:36:33.953: E/AndroidRuntime(13177): FATAL EXCEPTION: main
11-04 16:36:33.953: E/AndroidRuntime(13177): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.game.myapp/com.game.myapp.InGame}: java.lang.InstantiationException: com.game.myapp.InGame
11-04 16:36:33.953: E/AndroidRuntime(13177): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1573)
11-04 16:36:33.953: E/AndroidRuntime(13177): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
11-04 16:36:33.953: E/AndroidRuntime(13177): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
11-04 16:36:33.953: E/AndroidRuntime(13177): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
11-04 16:36:33.953: E/AndroidRuntime(13177): at android.os.Handler.dispatchMessage(Handler.java:99)
11-04 16:36:33.953: E/AndroidRuntime(13177): at android.os.Looper.loop(Looper.java:130)
11-04 16:36:33.953: E/AndroidRuntime(13177): at android.app.ActivityThread.main(ActivityThread.java:3687)
11-04 16:36:33.953: E/AndroidRuntime(13177): at java.lang.reflect.Method.invokeNative(Native Method)
11-04 16:36:33.953: E/AndroidRuntime(13177): at java.lang.reflect.Method.invoke(Method.java:507)
11-04 16:36:33.953: E/AndroidRuntime(13177): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:842)
11-04 16:36:33.953: E/AndroidRuntime(13177): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
11-04 16:36:33.953: E/AndroidRuntime(13177): at dalvik.system.NativeStart.main(Native Method)
11-04 16:36:33.953: E/AndroidRuntime(13177): Caused by: java.lang.InstantiationException: com.game.myapp.InGame
11-04 16:36:33.953: E/AndroidRuntime(13177): at java.lang.Class.newInstanceImpl(Native Method)
11-04 16:36:33.953: E/AndroidRuntime(13177): at java.lang.Class.newInstance(Class.java:1409)
11-04 16:36:33.953: E/AndroidRuntime(13177): at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
11-04 16:36:33.953: E/AndroidRuntime(13177): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1565)
11-04 16:36:33.953: E/AndroidRuntime(13177): ... 11 more
最佳答案
这是完整的代码。我刚刚写了这个并测试了它。有用。我在 Activity 中添加了一个计时器，每秒将球向右和向下移动 10 个像素。请研究它，从中学习并根据您的需要进行调整。
球类。
package com.example;
import android.graphics.Canvas;
import android.graphics.Paint;
public class Ball{
private int radius;
private int xPosition;
private int yPosition;
private int color;
private Paint paint;
public Ball(int x, int y, int radius, int color)
{
this.xPosition = x; this.yPosition = y; this.radius = radius;
paint = new Paint();
paint.setColor(color);
}
int getX(){return this.xPosition;}
int getY(){return this.yPosition;}
void moveBall(int x, int y){
xPosition = x; yPosition =y;
}
void onDraw(Canvas canvas){
canvas.drawCircle(xPosition, yPosition, radius, paint);
}
}
Playground 类
package com.example;
import android.content.Context;
import android.graphics.Canvas;
import android.util.AttributeSet;
import android.widget.ImageView;
public class Playground extends ImageView {
private Ball ball;
public Playground(Context context) {
this(context,null);
}
public Playground(Context context, AttributeSet attrs) {
this(context, attrs,0);
}
public Playground(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
public void setBall(Ball ball){
this.ball = ball;
}
@Override
public void onDraw(Canvas canvas)
{
super.onDraw(canvas);
if (ball != null ){
ball.onDraw(canvas);
}
}
}
Activity 类
package com.example;
import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;
import java.util.Timer;
import java.util.TimerTask;
public class MyActivity extends Activity {
/**
* Called when the activity is first created.
*/
Playground playground;
Ball ball;
Timer myTimer;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
playground = (Playground) findViewById(R.id.playground);
ball = new Ball(100, 100, 20, Color.RED);
playground.setBall(ball);
myTimer = new Timer();
myTimer.schedule(new TimerTask() {
@Override
public void run() {
Update();
}
}, 0, 1000);
}
private void Update() {
this.runOnUiThread(moveBall);
}
private Runnable moveBall = new Runnable() {
public void run() {
ball.moveBall(ball.getX() + 10, ball.getY() + 10);
playground.invalidate();
}
};
}
[编辑] XML
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<com.example.Playground
android:id="@+id/playground"
android:layout_width="fill_parent"
android:layout_height="fill_parent"/>
</LinearLayout>
OOP 的要点。
The Ball 对 Playground 或 Activity 一无所知。它有一个方法，可能被一些要求它在 Canvas 上绘制的东西调用，但据它所知，它可能是一个不可见的 Canvas ，或者一个按钮的 Canvas ，或者一个位图的 Canvas - 它不知道或不需要知道。这是调用方法的任何人的工作。
Playground 对 Activity 或球一无所知。它知道它可能有一个 Ball 类的实例，如果有，它应该调用它的 onDraw 方法，但它不知道球是什么或它绘制的是什么。 The Ball 对此很担心。
Activity 不知道 Ball 或 Playground，只是知道其中之一，并调用 Ball move 方法，然后告诉 Playground 重新绘制自己。
重点是，您可以更改绘制方法、移动方法和其他所有内容而无需重新编码(好的，一般来说)。例如，您可以更改 Ball 类中的 onDraw 以绘制一个矩形。当然，类的名称现在是一个糟糕的选择，但你明白了......
关于android - 在 Android 中创建游戏引力(续)？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/13240160/