相机放大/缩小空指针异常

Question

当我添加缩放代码时，我的代码工作正常，它给出了空指针异常。 我在预览类中编写了以下代码。我是android新手，请提前帮助谢谢。

我的代码是

       int currentZoomLevel = 0, maxZoomLevel = 0;

         public void surfaceChanged(SurfaceHolder surfaceHolder, int format,
                int width, int height) {
                  // start preview with new settings

            try {
                  parameters = mCamera.getParameters();
               } catch (Exception e1) {
                // TODO Auto-generated catch block
      e1.printStackTrace();
      }

     Display display = ((WindowManager) context
         .getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay();

        if (display.getRotation() == Surface.ROTATION_0) {
               try {
                  parameters.setPreviewSize(height, width);
                  mCamera.setDisplayOrientation(90);
                } catch (Exception e) {

             e.printStackTrace();
                  }
        }

   if (display.getRotation() == Surface.ROTATION_90) {
 try {
     parameters.setPreviewSize(width, height);
} catch (Exception e) {

  e.printStackTrace();
 }
}

if (display.getRotation() == Surface.ROTATION_180) {
 try {
  parameters.setPreviewSize(height, width);
 } catch (Exception e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
  }

}

if (display.getRotation() == Surface.ROTATION_270) {
 try {
  parameters.setPreviewSize(width, height);
 mCamera.setDisplayOrientation(180);
} catch (Exception e) {
 // TODO Auto-generated catch block
 e.printStackTrace();
}

}

这是我开始缩放的时候。我在侧面布局中添加缩放控件

 ZoomControls zoomControls = (ZoomControls) findViewById(R.id.zoom);

if (parameters.isZoomSupported()) {
 final int maxZoomLevel = parameters.getMaxZoom();
 Log.i("max ZOOM ", "is " + maxZoomLevel);
 zoomControls.setIsZoomInEnabled(true);
 zoomControls.setIsZoomOutEnabled(true);

 zoomControls.setOnZoomInClickListener(new OnClickListener() {
  public void onClick(View v) {
   if (currentZoomLevel < maxZoomLevel) {
   currentZoomLevel++;
  mCamera.startSmoothZoom(currentZoomLevel);
  parameters.setZoom(currentZoomLevel);
  mCamera.setParameters(parameters);
 }
}

}）;

 zoomControls.setOnZoomOutClickListener(new OnClickListener() {
  public void onClick(View v) {
  if (currentZoomLevel > 0) {
   currentZoomLevel--;
   parameters.setZoom(currentZoomLevel);
   mCamera.setParameters(parameters);
  }
 }
});
} else
 zoomControls.setVisibility(View.GONE);

try {
 mCamera.setPreviewDisplay(surfaceHolder);
 mCamera.startPreview();
 } catch (Exception e) {
 // intentionally left blank for a test
}

}