问题描述
这是我自定义View 的源码:public class MyView extends View {private float px;private float py;private int flag ;private Bitmap map;public MyView(Context context,float p_x,float p_y,int flag) {super(context);this.px=p_x;this.py=p_y;this.flag=flag;System.out.println(px);} public MyView(Context context, AttributeSet attrs) {super(context, attrs);System.out.println("2");}protected void onDraw(Canvas canvas) {super.onDraw(canvas);if(flag==1){map=BitmapFactory.decodeResource(getResources(), R.drawable.star_circle_mo);}else{map=BitmapFactory.decodeResource(getResources(), R.drawable.star_circle_mo1);}System.out.println("p_x"+px);System.out.println("p_y"+py);canvas.drawBitmap(map, 45.0f, 180.0f, null);}}在这里面调用它：public class PicBuyDemo extends Activity {private ImageView iv;private MyView myView;private MyView ball; public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); requestWindowFeature(Window.FEATURE_NO_TITLE); setContentView(R.layout.main); iv=(ImageView)findViewById(R.id.iv); ball=(MyView)findViewById(R.id.myView_01); iv.setBackgroundResource(R.drawable.j1); myView =new MyView(this,80.0f,70.0f,1); iv.setOnTouchListener(new OnTouchListener() {public boolean onTouch(View v, MotionEvent event) {ball.setVisibility(View.VISIBLE);return false;}}); }}布局文件:<?xml version="1.0" encoding="utf-8"?><FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:id="@+id/ll" ><ImageView android:id="@+id/iv"android:layout_width="fill_parent"android:layout_height="fill_parent"/><com.cyc.MyViewandroid:id="@+id/myView_01"android:layout_width="wrap_content"android:layout_height="wrap_content"android:visibility="gone"></com.cyc.MyView></FrameLayout>为什么在自定义View的ondraw()方法里px，py总是为0.0，flag=0 问题补充：你说的对，我后来想明白了
解决方案
myView =new MyView(this,80.0f,70.0f,1); （1）这一行根本没有任何用处ball=(MyView)findViewById(R.id.myView_01); （2）这句话是从xml读出MyView，调用的构造方法是public MyView(Context context, AttributeSet attrs)你在代码（1）中创建的这个myView根本就没有加入到布局中，也自然没有执行它的onDraw。