android - Android 应用程序运行时出现致命异常？

Question

我正在 Android 中开发一个小应用程序，我必须在其中显示图像。我的应用程序中有 2 张图像，但我必须通过手指触摸来移动图像，因此我在我的应用程序中使用了 viewflipper，并且我还想要放大和缩小功能。

我还为 xoom in 和 out 创建了 3 个类。但是当我运行该应用程序时，它会显示第一张图像，并在 itouch 和翻转时缩放它，然后我将它翻转回来并移动到第二张图像尝试缩放它我的应用程序将崩溃并在 logcat 中给出以下消息

06-17 15:22:17.003: ERROR/AndroidRuntime(6770): FATAL EXCEPTION: main 
06-17 15:22:17.003: ERROR/AndroidRuntime(6770): java.lang.ClassCastException: android.widget.LinearLayout 
06-17 15:22:17.003: ERROR/AndroidRuntime(6770):     at org.example.touch.Touch.onTouch(Touch.java:117) 
06-17 15:22:17.003: ERROR/AndroidRuntime(6770):     at android.view.View.dispatchTouchEvent(View.java:3762) 
06-17 15:22:17.003: ERROR/AndroidRuntime(6770):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:897) 
06-17 15:22:17.003: ERROR/AndroidRuntime(6770):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:863) 
06-17 15:22:17.003: ERROR/AndroidRuntime(6770):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:863) 
06-17 15:22:17.003: ERROR/AndroidRuntime(6770):     at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1671) 
06-17 15:22:17.003: ERROR/AndroidRuntime(6770):     at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1107) 
06-17 15:22:17.003: ERROR/AndroidRuntime(6770):     at android.app.Activity.dispatchTouchEvent(Activity.java:2086) 
06-17 15:22:17.003: ERROR/AndroidRuntime(6770):     at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1655) 
06-17 15:22:17.003: ERROR/AndroidRuntime(6770):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1785) 
06-17 15:22:17.003: ERROR/AndroidRuntime(6770):     at android.os.Handler.dispatchMessage(Handler.java:99) 
06-17 15:22:17.003: ERROR/AndroidRuntime(6770):     at android.os.Looper.loop(Looper.java:123) 
06-17 15:22:17.003: ERROR/AndroidRuntime(6770):     at android.app.ActivityThread.main(ActivityThread.java:4627) 
06-17 15:22:17.003: ERROR/AndroidRuntime(6770):     at java.lang.reflect.Method.invokeNative(Native Method) 
06-17 15:22:17.003: ERROR/AndroidRuntime(6770):     at java.lang.reflect.Method.invoke(Method.java:521) 
06-17 15:22:17.003: ERROR/AndroidRuntime(6770):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 
06-17 15:22:17.003: ERROR/AndroidRuntime(6770):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 
06-17 15:22:17.003: ERROR/AndroidRuntime(6770):     at dalvik.system.NativeStart.main(Native Method)

这是我的java代码

/***
 * Excerpted from "Hello, Android! 3e",
 * published by The Pragmatic Bookshelf.
 * Copyrights apply to this code. It may not be used to create training material, 
 * courses, books, articles, and the like. Contact us if you are in doubt.
 * We make no guarantees that this code is fit for any purpose. 
 * Visit http://www.pragmaticprogrammer.com/titles/eband3 for more book information.
***/
package org.example.touch;



import android.app.Activity;
import android.graphics.Matrix;
import android.graphics.PointF;
import android.os.Bundle;
import android.util.FloatMath;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.ViewFlipper;

public class Touch extends Activity implements OnTouchListener {
   private static final String TAG = "Touch";
   // These matrices will be used to move and zoom image
   Matrix matrix = new Matrix();
   Matrix savedMatrix = new Matrix();

   // We can be in one of these 3 states
   static final int NONE = 0;
   static final int DRAG = 1;
   static final int ZOOM = 2;
   int mode = NONE;
  float downXValue;
  int counter = 0;
   // Remember some things for zooming
   PointF start = new PointF();
   PointF mid = new PointF();
   float oldDist = 1f;

   @Override
   public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.main);
      ImageView view = (ImageView) findViewById(R.id.imageView);
      ImageView view1 = (ImageView) findViewById(R.id.imageView1);
      view.setOnTouchListener(this);
      LinearLayout layMain = (LinearLayout) findViewById(R.id.layout_main);
      layMain.setOnTouchListener((OnTouchListener) this); 

      // ...
      // Work around a Cupcake bug
      matrix.setTranslate(1f, 1f);
      view.setImageMatrix(matrix);
      view1.setImageMatrix(matrix);
   }
   @Override
  /* public boolean onTouch(View arg0, MotionEvent arg1) {

       // Get the action that was done on this touch event
       switch (arg1.getAction())
       {
           case MotionEvent.ACTION_DOWN:
           {
               // store the X value when the user's finger was pressed down
               downXValue = arg1.getX();
               break;
           }

           case MotionEvent.ACTION_UP:
           {
               // Get the X value when the user released his/her finger
               float currentX = arg1.getX();            

               // going backwards: pushing stuff to the right
               if (downXValue < currentX)
               {
                   // Get a reference to the ViewFlipper
                    ViewFlipper vf = (ViewFlipper) findViewById(R.id.details);
                    // Set the animation
                    // vf.setAnimation(AnimationUtils.loadAnimation(this, R.anim.push_left_out));
                     // Flip!
                    if(counter > 0){


                     vf.showPrevious();
                     counter--;
               }
               }

               // going forwards: pushing stuff to the left
               if (downXValue > currentX)
               {
                   // Get a reference to the ViewFlipper
                   ViewFlipper vf = (ViewFlipper) findViewById(R.id.details);
                    // Set the animation
                   //vf.setInAnimation(AnimationUtils.loadAnimation(this, R.anim.push_left_in));
                     // Flip!
                   if(counter < 1){
                    vf.showNext();
                    counter++;
                   }
               }
               break;
           }
       }

       // if you return false, these actions will not be recorded
       return true;
   }*/
   public boolean onTouch(View v, MotionEvent rawEvent) {
      WrapMotionEvent event = WrapMotionEvent.wrap(rawEvent);
      // ...
      ImageView view = (ImageView) v;

      // Dump touch event to log
      dumpEvent(event);

      // Handle touch events here...
      switch (event.getAction() & MotionEvent.ACTION_MASK) {
      case MotionEvent.ACTION_DOWN:
         savedMatrix.set(matrix);
         start.set(event.getX(), event.getY());
         Log.d(TAG, "mode=DRAG");
         mode = DRAG;
         downXValue = rawEvent.getX();
         break;
      case MotionEvent.ACTION_POINTER_DOWN:
         oldDist = spacing(event);
         Log.d(TAG, "oldDist=" + oldDist);
         if (oldDist > 10f) {
            savedMatrix.set(matrix);
            midPoint(mid, event);
            mode = ZOOM;
            Log.d(TAG, "mode=ZOOM");
         }
         break;
      case MotionEvent.ACTION_UP:
      {
          // Get the X value when the user released his/her finger
          float currentX = rawEvent.getX();            

          // going backwards: pushing stuff to the right
          if (downXValue < currentX)
          {
              // Get a reference to the ViewFlipper
               ViewFlipper vf = (ViewFlipper) findViewById(R.id.details);
               // Set the animation
               // vf.setAnimation(AnimationUtils.loadAnimation(this, R.anim.push_left_out));
                // Flip!
               if(counter > 0){


                vf.showPrevious();
                counter--;
          }
          }

          // going forwards: pushing stuff to the left
          if (downXValue > currentX)
          {
              // Get a reference to the ViewFlipper
              ViewFlipper vf = (ViewFlipper) findViewById(R.id.details);
               // Set the animation
              //vf.setInAnimation(AnimationUtils.loadAnimation(this, R.anim.push_left_in));
                // Flip!
              if(counter < 1){
               vf.showNext();
               counter++;
              }
          }
      }
      case MotionEvent.ACTION_POINTER_UP:
         mode = NONE;
         Log.d(TAG, "mode=NONE");

         break;
      case MotionEvent.ACTION_MOVE:
         if (mode == DRAG) {
            // ...
            matrix.set(savedMatrix);
            matrix.postTranslate(event.getX() - start.x,
                  event.getY() - start.y);
         }
         else if (mode == ZOOM) {
            float newDist = spacing(event);
            Log.d(TAG, "newDist=" + newDist);
            if (newDist > 10f) {
               matrix.set(savedMatrix);
               float scale = newDist / oldDist;
               matrix.postScale(scale, scale, mid.x, mid.y);
            }
         }
         break;
      }

      view.setImageMatrix(matrix);
      return true; // indicate event was handled
   }

   /** Show an event in the LogCat view, for debugging */
   private void dumpEvent(WrapMotionEvent event) {
      // ...
      String names[] = { "DOWN", "UP", "MOVE", "CANCEL", "OUTSIDE",
            "POINTER_DOWN", "POINTER_UP", "7?", "8?", "9?" };
      StringBuilder sb = new StringBuilder();
      int action = event.getAction();
      int actionCode = action & MotionEvent.ACTION_MASK;
      sb.append("event ACTION_").append(names[actionCode]);
      if (actionCode == MotionEvent.ACTION_POINTER_DOWN
            || actionCode == MotionEvent.ACTION_POINTER_UP) {
         sb.append("(pid ").append(
               action >> MotionEvent.ACTION_POINTER_ID_SHIFT);
         sb.append(")");
      }
      sb.append("[");
      for (int i = 0; i < event.getPointerCount(); i++) {
         sb.append("#").append(i);
         sb.append("(pid ").append(event.getPointerId(i));
         sb.append(")=").append((int) event.getX(i));
         sb.append(",").append((int) event.getY(i));
         if (i + 1 < event.getPointerCount())
            sb.append(";");
      }
      sb.append("]");
      Log.d(TAG, sb.toString());
   }

   /** Determine the space between the first two fingers */
   private float spacing(WrapMotionEvent event) {
      // ...
      float x = event.getX(0) - event.getX(1);
      float y = event.getY(0) - event.getY(1);
      return FloatMath.sqrt(x * x + y * y);
   }

   /** Calculate the mid point of the first two fingers */
   private void midPoint(PointF point, WrapMotionEvent event) {
      // ...
      float x = event.getX(0) + event.getX(1);
      float y = event.getY(0) + event.getY(1);
      point.set(x / 2, y / 2);
   }
}

Answer 1

当您将 v 转换到 ImageView 时，您会收到 ClassCastException。这意味着用户触摸了不是 ImageView 的 View 。

为了避免这种情况，您可以在 onCreate 方法中删除下一行代码 (51, 52):

LinearLayout layMain = (LinearLayout) findViewById(R.id.layout_main);
layMain.setOnTouchListener((OnTouchListener) this); 

或者在第 116 行的 onTouch 方法中添加一个额外的检查:

if(!(v instanceof ImageView))return false;