我不确定这意味着什么，但我现在看到的错误实际上是不同的，之后我关闭android studio重新打开它，这个错误发生了......
我的代码中没有错误，但这个应用程序无法编译，这非常令人沮丧。
12-21 23:20:02.007 6867-6867/zafir.com.motive E/AndroidRuntime: FATAL EXCEPTION: main
Process: zafir.com.motive, PID: 6867
java.lang.RuntimeException: Unable to instantiate application zafir.com.motive.Volley.MySingleton: java.lang.ClassCastException: zafir.com.motive.Volley.MySingleton cannot be cast to android.app.Application
at android.app.LoadedApk.makeApplication(LoadedApk.java:563)
at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4555)
at android.app.ActivityThread.access$1600(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1379)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5283)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)
Caused by: java.lang.ClassCastException: zafir.com.motive.Volley.MySingleton cannot be cast to android.app.Application
at android.app.Instrumentation.newApplication(Instrumentation.java:995)
at android.app.Instrumentation.newApplication(Instrumentation.java:980)
at android.app.LoadedApk.makeApplication(LoadedApk.java:558)
at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4555)
at android.app.ActivityThread.access$1600(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1379)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5283)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)
MainActivity
public class MainActivity extends AppCompatActivity
{
private static final String API_URL = "LINK";
private List<Photo> listPhotos = new ArrayList<Photo>();
private ImageLoader imageLoader;
private RecyclerView recView;
private RecyclerAdapter adapter;
RequestQueue requestQueue = Volley.newRequestQueue(this);
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//Initializing the RecyclerView and it's layout
recView = (RecyclerView) findViewById(R.id.recyclerview);
adapter = new RecyclerAdapter(MainActivity.this, (ArrayList<Photo>) listPhotos);
recView.setAdapter(adapter);
StaggeredGridLayoutManager gridLayoutManager = new StaggeredGridLayoutManager(3, StaggeredGridLayoutManager.HORIZONTAL);
recView.setLayoutManager(gridLayoutManager);
sendJSONRequest();
}
private void sendJSONRequest()
{
JsonObjectRequest request = new JsonObjectRequest(API_URL, null, new Response.Listener<JSONObject>()
{
@Override
public void onResponse(JSONObject response)
{
try
{
JSONObject objectRes = response.getJSONObject("response");
JSONArray arrayPosts = objectRes.getJSONArray("posts");
for (int i = 0; i < arrayPosts.length(); i++)
{
JSONObject object = arrayPosts.getJSONObject(i);
JSONArray arrayPhotos = object.getJSONArray("photos");
for (int j = 0; j < arrayPhotos.length(); j++)
{
JSONObject firstPhoto = arrayPhotos.getJSONObject(i);
JSONObject originalSize = firstPhoto.optJSONObject("original_size");
String url = originalSize.getString("url");
Photo photo = new Photo();
photo.setthumbnail(url);
listPhotos.add(photo);
}
}
} catch (JSONException e)
{
}
adapter.notifyDataSetChanged();
}
}, new Response.ErrorListener()
{
@Override
public void onErrorResponse(VolleyError error)
{
VolleyLog.e("Error: ", error.getMessage());
}
});
requestQueue.add(request);
}
RecyclerAdapter
public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.ViewHolder>
{
private Context context;
private List<Photo> listPhotos;
private MySingleton mySingleton;
private ImageLoader imageLoader;
private LayoutInflater layoutInflater;
private ViewHolder viewHolder;
private int focusedItem = 0;
public class ViewHolder extends RecyclerView.ViewHolder
{
//If this doesn't work change back to ImageView
public NetworkImageView thumbnail;
public ViewHolder(View itemView)
{
super(itemView);
this.thumbnail = (NetworkImageView) itemView.findViewById(R.id.rec_image);
}
}
public RecyclerAdapter(Context context, ArrayList<Photo> arrayList)
{
this.listPhotos = arrayList;
this.context = context;
}
public void setPhotos(ArrayList<Photo> photos)
{
this.listPhotos = photos;
notifyItemRangeChanged(0, listPhotos.size());
}
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType)
{
Context context = parent.getContext();
LayoutInflater inflater = LayoutInflater.from(context);
View recyclerViewLayout = LayoutInflater.from(parent.getContext()).inflate(R.layout.recyclerview_layout,null);
ViewHolder viewHolder = new ViewHolder(recyclerViewLayout);
return new ViewHolder(recyclerViewLayout);
}
@Override
public void onBindViewHolder(final ViewHolder holder, int position)
{
Photo currentPhoto = listPhotos.get(position);
imageLoader = MySingleton.getInstance(context).getImageLoader();
viewHolder.itemView.setSelected(focusedItem == position);
viewHolder.getLayoutPosition();
viewHolder.thumbnail.setImageUrl(currentPhoto.getthumbnail(), imageLoader);
//viewHolder.thumbnail.setDefaultImageResId(R.drawable.ic_view_quilt_black_36dp);
}
@Override
public int getItemCount()
{
return listPhotos.size();
}
}
MySingleton
public class MySingleton extends Activity
{
private static MySingleton mInstance;
private RequestQueue mRequestQueue;
private ImageLoader mImageLoader;
private static Context mCtx;
public MySingleton()
{
}
public MySingleton(Context context)
{
mCtx = context;
mRequestQueue = getRequestQueue();
mImageLoader = new ImageLoader(mRequestQueue, new LruBitmapCache(LruBitmapCache.getCacheSize(mCtx)));
}
public static synchronized MySingleton getInstance(Context context)
{
if (mInstance == null)
{
mInstance = new MySingleton(context);
}
return mInstance;
}
public RequestQueue getRequestQueue()
{
if (mRequestQueue == null)
{
// getApplicationContext() is key, it keeps you from leaking the
// Activity or BroadcastReceiver if someone passes one in.
mRequestQueue = Volley.newRequestQueue(mCtx.getApplicationContext());
}
return mRequestQueue;
}
public <T> void addToRequestQueue(Request<T> req)
{
getRequestQueue().add(req);
}
public ImageLoader getImageLoader()
{
return mImageLoader;
}
}
LruBitMapCache
public class LruBitmapCache extends LruCache<String, Bitmap>
implements ImageLoader.ImageCache
{
public LruBitmapCache(int maxSize) {
super(maxSize);
}
public LruBitmapCache(Context ctx) {
this(getCacheSize(ctx));
}
@Override
protected int sizeOf(String key, Bitmap value) {
return value.getRowBytes() * value.getHeight();
}
@Override
public Bitmap getBitmap(String url) {
return get(url);
}
@Override
public void putBitmap(String url, Bitmap bitmap) {
put(url, bitmap);
}
// Returns a cache size equal to approximately three screens worth of images.
public static int getCacheSize(Context ctx) {
final DisplayMetrics displayMetrics = ctx.getResources().
getDisplayMetrics();
final int screenWidth = displayMetrics.widthPixels;
final int screenHeight = displayMetrics.heightPixels;
// 4 bytes per pixel
final int screenBytes = screenWidth * screenHeight * 4;
return screenBytes * 3;
}
}
照片
public class Photo
{
private String thumbnail;
//----------Constructor----------
public Photo(String urlImage)
{
this.thumbnail = urlImage;
}
public Photo()
{
}
//----------Get-and-Set----------
public String getthumbnail()
{
return thumbnail;
}
public void setthumbnail(String thumbnail)
{
this.thumbnail = thumbnail;
}
//----------ToString-------------
@Override
public String toString()
{
return "urlImage" + thumbnail;
}
}
答案 0 :(得分：1)
你的MySingleton类应该扩展android.app.Application而不是Activity
class MySingleton extends android.app.Application// not Activity
答案 1 :(得分：0)
您的问题是：Caused by: java.lang.ClassCastException: zafir.com.motive.Volley.MySingleton cannot be cast to android.app.Application。您的MySingleton扩展自Activity类，而不是Application类的继承。
答案 2 :(得分：0)
在logcat错误中清楚地提到并由mr.icetea解释
问题：由java.lang.ClassCastException引起的崩溃：zafir.com.motive.Volley.MySingleton无法强制转换为android.app.Application。你的MySingleton从Activity类扩展而来，它不是Application类的继承
的解决方案：
在线下更改
mRequestQueue = Volley.newRequestQueue(mCtx.getApplicationContext());
到
mRequestQueue = Volley.newRequestQueue(mCtx);
答案 3 :(得分：0)
zafir.com.motive.Volley.MySingleton无法转换为android.app.Application。 MySingleton扩展自Activity类，它不是Application类的继承。使用Application类扩展MySingleton，并在应用程序标记中的manifest中输入：
<application
android:name="zafir.com.motive.Volley.MySingleton"
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
答案 4 :(得分：0)
无需扩展类Activity。普通班更合适。
而且，是自己写的Volley班吗？我搜索过，找不到这个类的库。也许这一行：RequestQueue requestQueue = Volley.newRequestQueue(this);导致错误。你能用Volley.newRequestQueue()方法发布代码吗？