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 个图像，但我必须提供通过手指触摸移动图像的功能，因此我在应用程序中使用视图翻转器，并且我还想要放大和缩小功能。

我还为 xoom 输入和输出创建了 3 个类。但是当我运行应用程序时，它会显示第一个图像，并且当 itouch 和翻转它时缩放它，它将移动到第二个图像，之后我将其翻转回来并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 转换为 ImageView 时，您会收到 ClassCastException。这意味着用户触摸的视图不是 ImageView。

为了避免这种情况，您可以删除 onCreate 方法中的下一行代码 (51, 52)：

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

或者在第 116 行的 onTouch 方法中添加额外的检查：

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