Android 为什么无效不起作用？

我试图画一个矩形，在这里我首先从Activity类中提供它的值，然后尝试从另一个类中更改它的坐标。。就我而言，逻辑是正确的，但无效无效无效。。我做了大量的研究，但还是没能成功

RectangleActivity.java

public class RectangleActivity extends Activity {

  private Point dStart = null;
  private Point dEnd = null;
  final private Handler handler = new Handler();
  Check check = new Check(this);
  Draw draw ;

  Runnable mUpdate = new Runnable()
    {
    public void run()
    {           
     Toast.makeText(getApplicationContext(), "update Called", Toast.LENGTH_LONG).show();
      check.update();           
    }
 };
      @Override
       public void onCreate(Bundle savedInstanceState) {        
        super.onCreate(savedInstanceState);
        dStart = new Point(0,0);
        dEnd = new Point(60,60);
        draw = new Draw(this,dStart,dEnd);
        setContentView(draw);
        handler.postDelayed(mUpdate, 4000); 
      } 
 }

    public class Check 
    {

  private Point start = new Point(80,80);
  private Point end = new Point(150,150);
  private Context context;

  public Check(Context context)
  {
    this.context =context;      
  } 
    void update() 
  { 
    Log.d("Aditi", "Update Called");
    Draw draw = new Draw(context);
    draw.reDraw(start,end);     
  } 
 }

    public class Draw extends View
    {   
 private Paint paint = null;
 private Point start = null;
 private Point end = null;  

 public Draw(Context context) 
  {
    super(context);     
    paint();    
  }     
  public Draw(Context context, Point start, Point end) 
  {
    super(context);

    this.start= start;
    this.end = end;
    paint();
  } 

   protected void onDraw(Canvas canvas)
   {
    super.onDraw(canvas);
    canvas.drawRect(start.x,start.y,end.x,end.y,paint);
    Log.d("Aditi", "OnDraw Called");
    System.out.println("StartX in ondraw is: "+start.x);
    System.out.println("StartY in ondraw is: "+start.y);
    System.out.println("EndX in ondraw is: "+end.x);
    System.out.println("EndY in ondraw is: "+end.y);    
  }

  public void reDraw(Point Start, Point End)
  {
    Log.d("Aditi", "Redraw Called");
    this.start = Start;
    this.end = End;
    invalidate();
    Log.d("Aditi", "Invalidate  Called");
    System.out.println("StartX in redraw is: "+start.x);
    System.out.println("StartY in redraw is: "+start.y);
    System.out.println("EndX in redraw is: "+end.x);
    System.out.println("EndY in redraw is: "+end.y);        
   }    
     public void paint()
   {
    paint= new Paint();     
    paint.setColor(Color.YELLOW);
    paint.setAntiAlias(true);
    paint.setStyle(Paint.Style.FILL_AND_STROKE);
  }   
}

检查.java

public class RectangleActivity extends Activity {

  private Point dStart = null;
  private Point dEnd = null;
  final private Handler handler = new Handler();
  Check check = new Check(this);
  Draw draw ;

  Runnable mUpdate = new Runnable()
    {
    public void run()
    {           
     Toast.makeText(getApplicationContext(), "update Called", Toast.LENGTH_LONG).show();
      check.update();           
    }
 };
      @Override
       public void onCreate(Bundle savedInstanceState) {        
        super.onCreate(savedInstanceState);
        dStart = new Point(0,0);
        dEnd = new Point(60,60);
        draw = new Draw(this,dStart,dEnd);
        setContentView(draw);
        handler.postDelayed(mUpdate, 4000); 
      } 
 }

    public class Check 
    {

  private Point start = new Point(80,80);
  private Point end = new Point(150,150);
  private Context context;

  public Check(Context context)
  {
    this.context =context;      
  } 
    void update() 
  { 
    Log.d("Aditi", "Update Called");
    Draw draw = new Draw(context);
    draw.reDraw(start,end);     
  } 
 }

    public class Draw extends View
    {   
 private Paint paint = null;
 private Point start = null;
 private Point end = null;  

 public Draw(Context context) 
  {
    super(context);     
    paint();    
  }     
  public Draw(Context context, Point start, Point end) 
  {
    super(context);

    this.start= start;
    this.end = end;
    paint();
  } 

   protected void onDraw(Canvas canvas)
   {
    super.onDraw(canvas);
    canvas.drawRect(start.x,start.y,end.x,end.y,paint);
    Log.d("Aditi", "OnDraw Called");
    System.out.println("StartX in ondraw is: "+start.x);
    System.out.println("StartY in ondraw is: "+start.y);
    System.out.println("EndX in ondraw is: "+end.x);
    System.out.println("EndY in ondraw is: "+end.y);    
  }

  public void reDraw(Point Start, Point End)
  {
    Log.d("Aditi", "Redraw Called");
    this.start = Start;
    this.end = End;
    invalidate();
    Log.d("Aditi", "Invalidate  Called");
    System.out.println("StartX in redraw is: "+start.x);
    System.out.println("StartY in redraw is: "+start.y);
    System.out.println("EndX in redraw is: "+end.x);
    System.out.println("EndY in redraw is: "+end.y);        
   }    
     public void paint()
   {
    paint= new Paint();     
    paint.setColor(Color.YELLOW);
    paint.setAntiAlias(true);
    paint.setStyle(Paint.Style.FILL_AND_STROKE);
  }   
}

Draw.java

public class RectangleActivity extends Activity {

  private Point dStart = null;
  private Point dEnd = null;
  final private Handler handler = new Handler();
  Check check = new Check(this);
  Draw draw ;

  Runnable mUpdate = new Runnable()
    {
    public void run()
    {           
     Toast.makeText(getApplicationContext(), "update Called", Toast.LENGTH_LONG).show();
      check.update();           
    }
 };
      @Override
       public void onCreate(Bundle savedInstanceState) {        
        super.onCreate(savedInstanceState);
        dStart = new Point(0,0);
        dEnd = new Point(60,60);
        draw = new Draw(this,dStart,dEnd);
        setContentView(draw);
        handler.postDelayed(mUpdate, 4000); 
      } 
 }

    public class Check 
    {

  private Point start = new Point(80,80);
  private Point end = new Point(150,150);
  private Context context;

  public Check(Context context)
  {
    this.context =context;      
  } 
    void update() 
  { 
    Log.d("Aditi", "Update Called");
    Draw draw = new Draw(context);
    draw.reDraw(start,end);     
  } 
 }

    public class Draw extends View
    {   
 private Paint paint = null;
 private Point start = null;
 private Point end = null;  

 public Draw(Context context) 
  {
    super(context);     
    paint();    
  }     
  public Draw(Context context, Point start, Point end) 
  {
    super(context);

    this.start= start;
    this.end = end;
    paint();
  } 

   protected void onDraw(Canvas canvas)
   {
    super.onDraw(canvas);
    canvas.drawRect(start.x,start.y,end.x,end.y,paint);
    Log.d("Aditi", "OnDraw Called");
    System.out.println("StartX in ondraw is: "+start.x);
    System.out.println("StartY in ondraw is: "+start.y);
    System.out.println("EndX in ondraw is: "+end.x);
    System.out.println("EndY in ondraw is: "+end.y);    
  }

  public void reDraw(Point Start, Point End)
  {
    Log.d("Aditi", "Redraw Called");
    this.start = Start;
    this.end = End;
    invalidate();
    Log.d("Aditi", "Invalidate  Called");
    System.out.println("StartX in redraw is: "+start.x);
    System.out.println("StartY in redraw is: "+start.y);
    System.out.println("EndX in redraw is: "+end.x);
    System.out.println("EndY in redraw is: "+end.y);        
   }    
     public void paint()
   {
    paint= new Paint();     
    paint.setColor(Color.YELLOW);
    paint.setAntiAlias(true);
    paint.setStyle(Paint.Style.FILL_AND_STROKE);
  }   
}

---

请随时指出我做错了什么。。提前谢谢。

如果这对你不起作用，恐怕我会的。请尝试调用invalidate方法onDraw（）

---

在上面的问题中，在onCreate（）中，您使用draw=newdraw（this，dStart，dEnd）进行查看 然后在setContentView（draw）中使用，但是当update（）调用时，您再次使用draw draw=new draw创建了一个draw对象（this，dStart，dEnd）并在第二个draw对象上调用draw.reDraw（start，end），这样setContentView（）中使用的实例就不会失效，第二个draw视图对象也会失效，但它没有传递到setContentView（），所以它在ui上不可见：您的解决方案只是

    void update() {
    //    Draw draw = new Draw(context);  //remove this
        draw.reDraw(start, end);
    }

---

如果从应用程序主线程以外的线程使视图无效，则该视图将无法工作，您必须调用postInvalidate（）而不是invalidate（）。

我可以通过调用postInvalidate（）方法，即draw.postInvalidate（）从Check.java调用onDraw方法它用更新后的矩形坐标调用onDraw方法。。