Android On Touch

Question

我一直在尝试让一个程序在我触摸屏幕时画圆圈，但没有成功，有人能告诉我怎么做吗？或者一个好的教程，告诉我如何..。我的代码中不断出现错误

import android.content.Context;
import android.content.Intent;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.text.format.Time;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import java.lang.Math;

public class GameView extends View{

        private final float x;
        private final float y;
        private final int r;
        private final Paint mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);

        public GameView(Context context, float x, float y, int r) {
            super(context);
            setFocusable(true);
            mPaint.setColor(0xFFFF0000);
            this.x = x;
            this.y = y;
            this.r = r;
        }

        @Override
        protected void onDraw(Canvas canvas) {
            super.onDraw(canvas);
            canvas.drawCircle(x, y, r, mPaint);
        } 


}

GameActivity.java

import android.app.Activity; 
import android.content.Context;
import android.os.Bundle;   
import android.os.Handler;
import android.os.Message;
import android.view.Display;
import android.view.MotionEvent;
import android.view.View;
import android.view.WindowManager;
import android.widget.FrameLayout;

public class GameActivity extends Activity {    
    /** Called when the activity is first created. */ 
    @Override  
    public void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        FrameLayout main = (FrameLayout) findViewById(R.id.my_view); 

        main.setOnTouchListener(new View.OnTouchListener() {
            public boolean onTouch(final View v, MotionEvent e) {

                 final float x = e.getX();
                 final float y = e.getY();
                  final Handler handler = new Handler() 
                  {                  
                    public void handleMessage(Message msg) {



                      }                 
                    };          
                    Thread graphicThread = new Thread()       
                    {                        
                        public void run() {                              

                            try {

                                //Do the drop
                                   FrameLayout flView = (FrameLayout) v;
                                 GameView gm = new GameView(getParent(), x,y,25);
                                  flView.addView(gm);


                                     Thread.sleep(1000);

                                     handler.sendMessage(handler.obtainMessage());
                                }
                             catch (InterruptedException e) {
                                // TODO Auto-generated catch block
                                e.printStackTrace();
                            }

                        }                     
                        };                
                         boolean isRunning=true;
                        graphicThread.start();   
                        return true;

                        }           


        }); 


      }
    }

Answer 1

如果不是子活动，就不应该在活动中使用getParent()。

改用下面的代码：

GameView gm = new GameView(this, x, y, 25);

Answer 2

因为NPE问题已经回答了，所以我想提供教程问题的答案。我已经写了一个系列(部分更新)，你可以在这里找到:我已经为游戏写了一个关于2d图形的教程。请阅读：http://www.droidnova.com/2d-tutorial-series