我使用AsyncTask从SQLite数据库加载数据,然后使用StaggeredLayoutManager和CustomListAdapter将数据提供给Recycler View。
如果我没有在onPostExecuteMethod中关闭doInBackground方法的光标,则从上一个活动的转换是滞后的,并且android logcat说“跳过52帧”。
如果我关闭光标,在Post Execute方法结束时,不会发生延迟,但在Activity内部不会呈现任何内容。 (Recycler View没有任何内容。)
@Override
protected void onPostExecute(Void Void) {
c.close();
swipeRefreshLayout.setRefreshing(false);
swipeRefreshLayout.setOnRefreshListener(
new SwipeRefreshLayout.OnRefreshListener() {
@Override
public void onRefresh() {
new MyTask().execute();
}
});
swipeRefreshLayout.setColorSchemeColors(getResources().getIntArray(R.array.swipeRefreshColors));
}
try {
myDb = new SavedData(getApplicationContext());
writeableDatabase = myDb.getReadableDatabase();
final String[] projection = {SavedData.COLUMN_NAME_ENTRY_ID,
SavedData.COLUMN_NAME_PRICE,
SavedData.COLUMN_NAME_SHIPPING,
SavedData.COLUMN_NAME_WEIGHT,
SavedData.COLUMN_NAME_PRODUCT};
sortOrder = BookSave.COLUMN_NAME_ENTRY_ID + " DESC";
c = writeableDatabase.query(
SavedData.TABLE_NAME,
projection,
null,
null,
null,
null,
sortOrder
);
m = new MyListCursorAdapter(getApplicationContext(), c);
gaggeredGridLayoutManager = new StaggeredGridLayoutManager(NUM, 1);
} catch (Exception e) {
e.printStackTrace();
} finally {
}
import android.content.Context;
import android.database.Cursor;
import android.database.DataSetObserver;
import android.support.v7.widget.RecyclerView;
public abstract class CursorRecyclerViewAdapter<VH extends RecyclerView.ViewHolder> extends RecyclerView.Adapter<VH> {
private Context mContext;
private Cursor mCursor;
private boolean mDataValid;
private int mRowIdColumn;
private DataSetObserver mDataSetObserver;
public CursorRecyclerViewAdapter(Context context, Cursor cursor) {
mContext = context;
mCursor = cursor;
mDataValid = cursor != null;
mRowIdColumn = mDataValid ? mCursor.getColumnIndex("_id") : -1;
mDataSetObserver = new NotifyingDataSetObserver();
if (mCursor != null) {
mCursor.registerDataSetObserver(mDataSetObserver);
}
}
public Cursor getCursor() {
return mCursor;
}
@Override
public int getItemCount() {
if (mDataValid && mCursor != null) {
return mCursor.getCount();
}
return 0;
}
@Override
public long getItemId(int position) {
if (mDataValid && mCursor != null && mCursor.moveToPosition(position)) {
return mCursor.getLong(mRowIdColumn);
}
return 0;
}
@Override
public void setHasStableIds(boolean hasStableIds) {
super.setHasStableIds(true);
}
public abstract void onBindViewHolder(VH viewHolder, Cursor cursor);
@Override
public void onBindViewHolder(VH viewHolder, int position) {
if (!mDataValid) {
throw new IllegalStateException("this should only be called when the cursor is valid");
}
if (!mCursor.moveToPosition(position)) {
throw new IllegalStateException("couldn't move cursor to position " + position);
}
onBindViewHolder(viewHolder, mCursor);
}
/**
* Change the underlying cursor to a new cursor. If there is an existing cursor it will be
* closed.
*/
public void changeCursor(Cursor cursor) {
Cursor old = swapCursor(cursor);
if (old != null) {
old.close();
}
}
/**
* Swap in a new Cursor, returning the old Cursor. Unlike
* {@link #changeCursor(Cursor)}, the returned old Cursor is <em>not</em>
* closed.
*/
public Cursor swapCursor(Cursor newCursor) {
if (newCursor == mCursor) {
return null;
}
final Cursor oldCursor = mCursor;
if (oldCursor != null && mDataSetObserver != null) {
oldCursor.unregisterDataSetObserver(mDataSetObserver);
}
mCursor = newCursor;
if (mCursor != null) {
if (mDataSetObserver != null) {
mCursor.registerDataSetObserver(mDataSetObserver);
}
mRowIdColumn = newCursor.getColumnIndexOrThrow("_id");
mDataValid = true;
notifyDataSetChanged();
} else {
mRowIdColumn = -1;
mDataValid = false;
notifyDataSetChanged();
//There is no notifyDataSetInvalidated() method in RecyclerView.Adapter
}
return oldCursor;
}
private class NotifyingDataSetObserver extends DataSetObserver {
@Override
public void onChanged() {
super.onChanged();
mDataValid = true;
notifyDataSetChanged();
}
@Override
public void onInvalidated() {
super.onInvalidated();
mDataValid = false;
notifyDataSetChanged();
//There is no notifyDataSetInvalidated() method in RecyclerView.Adapter
}
}
}
import android.content.Context;
import android.content.Intent;
import android.content.res.Resources;
import android.database.Cursor;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Typeface;
import android.os.AsyncTask;
import android.support.v7.widget.CardView;
import android.support.v7.widget.RecyclerView;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.Display;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.WindowManager;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.TextView;
public class MyListCursorAdapter extends CursorRecyclerViewAdapter<MyListCursorAdapter.ViewHolder> {
private static final String TAG = "MyListCursorAdapter";
public MyListCursorAdapter(Context context, Cursor cursor) {
super(context, cursor);
}
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View itemView = LayoutInflater.from(parent.getContext())
.inflate(R.layout.productList, parent, false);
ViewHolder vh = new ViewHolder(itemView);
return vh;
}
@Override
public void onBindViewHolder(final ViewHolder viewHolder, final Cursor cursor) {
Book myListItem = Book.fromCursor(cursor);
viewHolder.titleTextView.setText(myListItem.getTitle());
viewHolder.shippingTextView.setText(myListItem.getAShipping());
Log.d(TAG, "onBindViewHolder: "+viewHolder.isRecyclable());
}
public static class ViewHolder extends RecyclerView.ViewHolder {
public TextView shippingTextView;
public TextView titleTextView;
public LinearLayout insideCard;
public Button payButton;
public View seperator;
public CardView cv;
public View view;
public ViewHolder(final View view) {
super(view);
WindowManager wm = (WindowManager) view.getContext().getSystemService(Context.WINDOW_SERVICE);
Display display = wm.getDefaultDisplay();
DisplayMetrics DM = new DisplayMetrics();
display.getMetrics(DM);
payButton = (Button) view.findViewById(R.id.readButton);
seperator = view.findViewById(R.id.separator);
titleTextView = (TextView) view.findViewById(R.id.titleTextView);
insideCard = (LinearLayout) view.findViewById(R.id.insideCard);
insideCard.getLayoutParams().width = (DM.widthPixels / 2) - 24;
shippingTextView = (TextView) view.findViewById(R.id.shippingTextView);
//typeface
Typeface light = Typeface.createFromAsset(titleTextView.getResources().getAssets(), "fonts/light.ttf");
titleTextView.setTypeface(light);
Typeface regular = Typeface.createFromAsset(authorTextView.getResources().getAssets(), "fonts/thinItalic.ttf");
shippingTextView.setTypeface(regular);
payButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent goToCheckout = new Intent(view.getContext(), ShowReader.class);
goToCheckout.putExtra("PRODUCT_NAME", titleTextView.getText());
view.getContext().startActivity(goToCheckout);
}
});
setWidth((DM.widthPixels / 2) - 24);
}
public void setWidth(int a) {
a = a - 8 * 4;
payButton.getLayoutParams().width = a;
seperator.getLayoutParams().width = a;
}
}
}
答案 0 :(得分:4)
在完成操作之前,不应关闭光标。一旦你完成了这些数据,你就失去了数据来源,这就是为什么你在关闭之后没有看到任何数据的原因。
你有没有分析过你的适配器?如果你没有关闭光标时出现滞后现象,但是没有关闭光标,那么你总是有可能无法有效地创建视图
答案 1 :(得分:4)
这是你的问题:
//typeface
Typeface light = Typeface.createFromAsset(titleTextView.getResources().getAssets(), "fonts/light.ttf");
titleTextView.setTypeface(light);
Typeface regular = Typeface.createFromAsset(authorTextView.getResources().getAssets(), "fonts/thinItalic.ttf");
shippingTextView.setTypeface(regular);
每次要创建新的ViewHolder
时,您都要从文件中读取。多次执行此操作时操作繁重。因此,一种解决方案是只读取一次并缓存字体。所以让我们看一些代码:
public class MyFontProvider {
private static final String TAG = MyFontProvider.class.getSimpleName();
private Map<String, Typeface> mCache;
private static volatile MyFontProvider sInstance;
public static MyFontProvider getInstance() {
if (sInstance == null) {
synchronized (MyFontProvider.class) {
if (sInstance == null) {
sInstance = new MyFontProvider();
}
}
}
return sInstance;
}
private MyFontProvider() {
mCache = new Hashtable<>();
}
public synchronized Typeface getFont(String assetPath, Context context) {
if (!mCache.containsKey(assetPath)) {
try {
Typeface t = Typeface.createFromAsset(context.getAssets(), assetPath);
mCache.put(assetPath, t);
} catch (Exception e) {
Log.e(TAG, "Error getting typeface (" + assetPath + " ) " + e.getMessage());
return null;
}
}
return mCache.get(assetPath);
}
}
现在你可以改变
//typeface
Typeface light = Typeface.createFromAsset(titleTextView.getResources().getAssets(), "fonts/light.ttf");
titleTextView.setTypeface(light);
Typeface regular = Typeface.createFromAsset(authorTextView.getResources().getAssets(), "fonts/thinItalic.ttf");
shippingTextView.setTypeface(regular);
到
//typeface
titleTextView.setTypeface(MyFontProvider.getInstance().getFont("fonts/light.ttf",this));
shippingTextView.setTypeface(MyFontProvider.getInstance().getFont("fonts/thinItalic.ttf",this));
最好将字体路径存储为public final static String
,以便您可以在一个位置更改它,而不必修改多个文件。