我在我的应用程序中尝试使用coverflow 我想在我的main.xml中使用具有特定尺寸的linearlayout中的coverflow。 我试过但是我得到了这个错误..
07-27 19:43:23.427: E/AndroidRuntime(1111): FATAL EXCEPTION: main
07-27 19:43:23.427: E/AndroidRuntime(1111): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.android/com.android.Coverflow_displayerActivity}: java.lang.NullPointerException
07-27 19:43:23.427: E/AndroidRuntime(1111): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1815)
07-27 19:43:23.427: E/AndroidRuntime(1111): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1831)
07-27 19:43:23.427: E/AndroidRuntime(1111): at android.app.ActivityThread.access$500(ActivityThread.java:122)
07-27 19:43:23.427: E/AndroidRuntime(1111): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1024)
07-27 19:43:23.427: E/AndroidRuntime(1111): at android.os.Handler.dispatchMessage(Handler.java:99)
07-27 19:43:23.427: E/AndroidRuntime(1111): at android.os.Looper.loop(Looper.java:132)
07-27 19:43:23.427: E/AndroidRuntime(1111): at android.app.ActivityThread.main(ActivityThread.java:4123)
07-27 19:43:23.427: E/AndroidRuntime(1111): at java.lang.reflect.Method.invokeNative(Native Method)
07-27 19:43:23.427: E/AndroidRuntime(1111): at java.lang.reflect.Method.invoke(Method.java:491)
07-27 19:43:23.427: E/AndroidRuntime(1111): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
07-27 19:43:23.427: E/AndroidRuntime(1111): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
07-27 19:43:23.427: E/AndroidRuntime(1111): at dalvik.system.NativeStart.main(Native Method)
07-27 19:43:23.427: E/AndroidRuntime(1111): Caused by: java.lang.NullPointerException
07-27 19:43:23.427: E/AndroidRuntime(1111): at com.android.Coverflow_displayerActivity.onCreate(Coverflow_displayerActivity.java:48)
07-27 19:43:23.427: E/AndroidRuntime(1111): at android.app.Activity.performCreate(Activity.java:4397)
07-27 19:43:23.427: E/AndroidRuntime(1111): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1048)
07-27 19:43:23.427: E/AndroidRuntime(1111): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1779)
07-27 19:43:23.427: E/AndroidRuntime(1111): ... 11 more
这是我试过的代码
package com.android;
import java.io.FileInputStream;
import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.LinearGradient;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.PorterDuff.Mode;
import android.graphics.PorterDuffXfermode;
import android.graphics.Shader.TileMode;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.ImageView.ScaleType;
import android.widget.Toast;
import com.android.CoverAdapterView.OnItemClickListener;
public class Coverflow_displayerActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
CoverFlow coverFlow = (CoverFlow) findViewById(R.id.coverflow);
//
// CoverFlow coverFlow;
// coverFlow= new CoverFlow(this);
coverFlow.setAdapter(new ImageAdapter(this));
ImageAdapter coverImageAdapter = new ImageAdapter(this);
coverImageAdapter.createReflectedImages();
coverFlow.setAdapter(coverImageAdapter);
coverFlow.setSpacing(-15);
coverFlow.setSelection(5, true);
setContentView(R.layout.main);
// setContentView(coverFlow);
coverFlow.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(CoverAdapterView<?> parent, View view,
int position, long id) {
// TODO Auto-generated method stub
Log.v("this happens only in india", "ok i know this position"
+ position);
Toast.makeText(getApplicationContext(), "position " + position,
Toast.LENGTH_SHORT).show();
}
});
// Use this if you want to use XML layout file
// setContentView(R.layout.main);
}
public class ImageAdapter extends BaseAdapter {
int mGalleryItemBackground;
private Context mContext;
private FileInputStream fis;
private Integer[] mImageIds = { R.drawable.kasabian_kasabian,
R.drawable.killers_day_and_age, R.drawable.garbage_bleed_like_me,
R.drawable.death_cub_for_cutie_the_photo_album,
R.drawable.kasabian_kasabian,
R.drawable.massive_attack_collected, };
private ImageView[] mImages;
public ImageAdapter(Context c) {
mContext = c;
mImages = new ImageView[mImageIds.length];
}
public boolean createReflectedImages() {
// The gap we want between the reflection and the original image
final int reflectionGap = 4;
int index = 0;
for (final int imageId : mImageIds) {
Bitmap originalImage = BitmapFactory.decodeResource(
getResources(), imageId);
int width = originalImage.getWidth();
int height = originalImage.getHeight();
// This will not scale but will flip on the Y axis
Matrix matrix = new Matrix();
matrix.preScale(1, -1);
// Create a Bitmap with the flip matrix applied to it.
// We only want the bottom half of the image
Bitmap reflectionImage = Bitmap.createBitmap(originalImage, 0,
height / 2, width, height / 2, matrix, false);
// Create a new bitmap with same width but taller to fit
// reflection
Bitmap bitmapWithReflection = Bitmap.createBitmap(width,
(height + height / 2), Config.ARGB_8888);
// Create a new Canvas with the bitmap that's big enough for
// the image plus gap plus reflection
Canvas canvas = new Canvas(bitmapWithReflection);
// Draw in the original image
canvas.drawBitmap(originalImage, 0, 0, null);
// Draw in the gap
Paint deafaultPaint = new Paint();
canvas.drawRect(0, height, width, height + reflectionGap,
deafaultPaint);
// Draw in the reflection
canvas.drawBitmap(reflectionImage, 0, height + reflectionGap,
null);
// Create a shader that is a linear gradient that covers the
// reflection
Paint paint = new Paint();
LinearGradient shader = new LinearGradient(0,
originalImage.getHeight(), 0,
bitmapWithReflection.getHeight() + reflectionGap,
0x70ffffff, 0x00ffffff, TileMode.CLAMP);
// Set the paint to use this shader (linear gradient)
paint.setShader(shader);
// Set the Transfer mode to be porter duff and destination in
paint.setXfermode(new PorterDuffXfermode(Mode.DST_IN));
// Draw a rectangle using the paint with our linear gradient
canvas.drawRect(0, height, width,
bitmapWithReflection.getHeight() + reflectionGap, paint);
ImageView imageView = new ImageView(mContext);
imageView.setImageBitmap(bitmapWithReflection);
imageView.setLayoutParams(new CoverFlow.LayoutParams(120, 180));
imageView.setScaleType(ScaleType.MATRIX);
mImages[index++] = imageView;
}
return true;
}
public int getCount() {
// Log.v("getCoutn(int count)", "" + mImageIds.length);
return mImageIds.length;
}
public Object getItem(int position) {
// Log.v("getItem(int position)", "" + position);
return position;
}
public long getItemId(int position) {
// Log.v("getItemID(int position)", "" + position);
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
// Use this code if you want to load from resources
// ImageView i = new ImageView(mContext);
// i.setImageResource(mImageIds[position]);
// i.setLayoutParams(new CoverFlow.LayoutParams(130, 130));
// i.setScaleType(ImageView.ScaleType.MATRIX);
// return i;
// Log.v("getview int position mImages", ""+position);
return mImages[position];
}
/**
* Returns the size (0.0f to 1.0f) of the views depending on the
* 'offset' to the center.
*/
public float getScale(boolean focused, int offset) {
/* Formula: 1 / (2 ^ offset) */
Log.v("getScale float ", " " + focused + " " + offset);
return Math.max(0, 1.0f / (float) Math.pow(2, Math.abs(offset)));
}
// View v=getView(position, convertView, parent);
}
}
main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello" />
<LinearLayout
android:id="@+id/add_here"
android:layout_width="700dp"
android:layout_height="700dp"
android:orientation="vertical"
android:background="@android:color/darker_gray"
>
<com.android.CoverFlow
android:id="@+id/coverflow"
android:layout_width="700dp"
android:layout_height="700dp" />
</LinearLayout>
</LinearLayout>
答案 0 :(得分：2)
首先需要设置活动视图，以便findViewById从该视图中获取ID并映射控件。所以写
setContentView(R.layout.main);，即
CoverFlow coverFlow = (CoverFlow) findViewById(R.id.coverflow);
答案 1 :(得分：2)
似乎是onCreate()中的错误。在尝试分配coverFlow（setContentView(R.layout.main);）之前，应调用CoverFlow coverFlow = (CoverFlow) findViewById(R.id.coverflow);。这就是为什么coverFlow是NULL。
答案 2 :(得分：2)
我同意这里的其他答案。问题是甚至在调用setContentView（）之前尝试初始化小部件。但我相信用户正在尝试遵循同样的事情，因为他无法区分从XML设置内容和在代码中创建视图并将其设置为内容。
在上面的例子中，如果你可以看到，作者试图在这里创建一个Coverflow视图代码，
CoverFlow coverFlow;
coverFlow= new CoverFlow(this);
然后他使用setContentView(coverFlow);
但在我们的案例中，我们使用XML生成的资源，
第一件事是使用setContentView()将xml映射到我们的Activity。因为只有这时系统才会知道它必须从我们使用SetContentView()提供给它的XML中查找资源。如果不是，它将导致NullPointerException，因为andorid将找不到资源，因为我们已经指定了查找的位置。
因此，对于您的情况，请按照上述答案提供
setContentView(R.layout.main);
首先，然后使用参考表单初始化您的视图，例如，
CoverFlow coverFlow = (CoverFlow) findViewById(R.id.coverflow);