Android：以編程方式初始化XML對象，其中有參數

Question

我有一個名爲CoverFlowClass的類。 我以前這樣做是爲了創建一個類，

CoverFlowClass coverFlow = new CoverFlowClass(this) 
coverFlow.setAdapter(new ImageAdapter(this)); 

但現在我想用XML，所以我可以做的布點。我創建一個XML代碼：

<id.co.ajsmsig.display.CoverFlowClass 
    android:id="@+id/coverflow" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
/> 

但是，當我從代碼創建這樣的：

CoverFlowClass coverFlow= (CoverFlowClass) findViewById(R.id.coverflow); 
coverFlow.setAdapter(new ImageAdapter(this)); 

我的應用程序強制關閉。 錯誤日誌中的logcat我發現是：

7月4日至18日：46：34.804：E/AndroidRuntime（1847）：在id.co.ajsmsig.display.CoverFlowMain.onCreate（CoverFlowMain.java:76 ）。

併線76：

coverFlow.setAdapter(new ImageAdapter(this)); 

我想是因爲該類使用它構造函數的參數（=新CoverFlowClass（本）），而findViewById不給任何參數。我仍然不知道，如何使這項工作？任何想法是讚賞。

謝謝

P.下面是的CoverFlow類的源代碼：

---

package id.co.ajsmsig.display; 


import android.content.Context; 
import android.graphics.Camera; 
import android.graphics.Matrix; 
import android.util.AttributeSet; 
import android.view.View; 
import android.view.animation.Transformation; 
import android.widget.Gallery; 
import android.widget.ImageView; 

public class CoverFlowClass extends Gallery { 

    /** 
    * Graphics Camera used for transforming the matrix of ImageViews 
    */ 
    private Camera mCamera = new Camera(); 

    /** 
    * The maximum angle the Child ImageView will be rotated by 
    */  
    private int mMaxRotationAngle = 60; 

    /** 
    * The maximum zoom on the centre Child 
    */ 
    private int mMaxZoom = -120; 

    /** 
    * The Centre of the Coverflow 
    */ 
    private int mCoveflowCenter; 

    public CoverFlowClass(Context context) { 
    super(context); 
    this.setStaticTransformationsEnabled(true); 
} 

    public CoverFlowClass(Context context, AttributeSet attrs) { 
    super(context, attrs); 
     this.setStaticTransformationsEnabled(true); 
} 

    public CoverFlowClass(Context context, AttributeSet attrs, int defStyle) { 
    super(context, attrs, defStyle); 
    this.setStaticTransformationsEnabled(true); 
    } 

    /** 
    * Get the max rotational angle of the image 
    * @return the mMaxRotationAngle 
    */ 
    public int getMaxRotationAngle() { 
    return mMaxRotationAngle; 
} 

/** 
    * Set the max rotational angle of each image 
    * @param maxRotationAngle the mMaxRotationAngle to set 
    */ 
    public void setMaxRotationAngle(int maxRotationAngle) { 
    mMaxRotationAngle = maxRotationAngle; 
} 

/** 
    * Get the Max zoom of the centre image 
    * @return the mMaxZoom 
    */ 
    public int getMaxZoom() { 
    return mMaxZoom; 
} 

/** 
    * Set the max zoom of the centre image 
    * @param maxZoom the mMaxZoom to set 
    */ 
    public void setMaxZoom(int maxZoom) { 
     mMaxZoom = maxZoom; 
    } 

/** 
    * Get the Centre of the Coverflow 
    * @return The centre of this Coverflow. 
    */ 
    private int getCenterOfCoverflow() { 
     return (getWidth() - getPaddingLeft() - getPaddingRight())/2 + getPaddingLeft(); 
    } 

    /** 
    * Get the Centre of the View 
    * @return The centre of the given view. 
    */ 
    private static int getCenterOfView(View view) { 
     return view.getLeft() + view.getWidth()/2; 
    } 
    /** 
    * {@inheritDoc} 
    * 
    * @see #setStaticTransformationsEnabled(boolean) 
    */ 
    protected boolean getChildStaticTransformation(View child, Transformation t) { 

    final int childCenter = getCenterOfView(child); 
    final int childWidth = child.getWidth() ; 
    int rotationAngle = 0; 

    t.clear(); 
    t.setTransformationType(Transformation.TYPE_MATRIX); 

     if (childCenter == mCoveflowCenter) { 
      transformImageBitmap((ImageView) child, t, 0); 
     } else {  
      rotationAngle = (int) (((float) (mCoveflowCenter - childCenter)/ childWidth) * mMaxRotationAngle); 
      if (Math.abs(rotationAngle) > mMaxRotationAngle) { 
      rotationAngle = (rotationAngle < 0) ? -mMaxRotationAngle : mMaxRotationAngle; 
      } 
      transformImageBitmap((ImageView) child, t, rotationAngle);   
     }  

    return true; 
} 

/** 
    * This is called during layout when the size of this view has changed. If 
    * you were just added to the view hierarchy, you're called with the old 
    * values of 0. 
    * 
    * @param w Current width of this view. 
    * @param h Current height of this view. 
    * @param oldw Old width of this view. 
    * @param oldh Old height of this view. 
    */ 
    protected void onSizeChanged(int w, int h, int oldw, int oldh) { 
     mCoveflowCenter = getCenterOfCoverflow(); 
     super.onSizeChanged(w, h, oldw, oldh); 
    } 

    /** 
    * Transform the Image Bitmap by the Angle passed 
    * 
    * @param imageView ImageView the ImageView whose bitmap we want to rotate 
    * @param t transformation 
    * @param rotationAngle the Angle by which to rotate the Bitmap 
    */ 
    private void transformImageBitmap(View child, Transformation t, int rotationAngle) {    
     mCamera.save(); 
     final Matrix imageMatrix = t.getMatrix();; 
     final int imageHeight = child.getLayoutParams().height;; 
     final int imageWidth = child.getLayoutParams().width; 
     final int rotation = Math.abs(rotationAngle); 

     mCamera.translate(0.0f, 0.0f, 100.0f); 

     //As the angle of the view gets less, zoom in  
     if (rotation < mMaxRotationAngle) { 
     float zoomAmount = (float) (mMaxZoom + (rotation * 1.5)); 
     mCamera.translate(0.0f, 0.0f, zoomAmount);   
     } 

     mCamera.rotateY(rotationAngle); 
     mCamera.getMatrix(imageMatrix);    
     imageMatrix.preTranslate(-(imageWidth/2), -(imageHeight/2)); 
     imageMatrix.postTranslate((imageWidth/2), (imageHeight/2)); 
     mCamera.restore(); 
} 
} 

Answer 1

這聽起來像你有一個NullPointerException：在findViewById調用實際上並沒有找到視圖，因爲它永遠不會實例化。您可能需要爲CoverFlowClass實現一個構造函數，該構造函數接受一個AttributeSet。也許是這樣的：

public CoverFlowClass(Context context, AttributeSet attrs) 
{ 
    super(context, attrs); 

     // do whatever other initialization is necessary 
} 

Answer 2

對不起，這個迴應有點晚了，但也許它會幫助那裏的人有類似的問題。它也認爲這聽起來像是NullPointerException，因此如果您打算在XML佈局中使用Coverflow，請務必在調用任何findViewById之前設置ContentView（R.layout.main）。您可以打印coverFlow的值以確保它不再爲空。