Java tutorial
/* * Copyright (C) 2012 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.manning.androidhacks.hack040; import android.content.Context; import android.content.Intent; import android.os.Bundle; import android.support.v4.app.Fragment; import android.util.Log; import android.util.TypedValue; import android.view.LayoutInflater; import android.view.Menu; import android.view.MenuInflater; import android.view.MenuItem; import android.view.View; import android.view.ViewGroup; import android.view.ViewGroup.LayoutParams; import android.view.ViewTreeObserver; import android.widget.AbsListView; import android.widget.AdapterView; import android.widget.BaseAdapter; import android.widget.GridView; import android.widget.ImageView; import android.widget.Toast; import com.manning.androidhacks.hack040.provider.Images; import com.manning.androidhacks.hack040.util.ImageCache; import com.manning.androidhacks.hack040.util.ImageCache.ImageCacheParams; import com.manning.androidhacks.hack040.util.ImageFetcher; import com.manning.androidhacks.hack040.util.ImageResizer; import com.manning.androidhacks.hack040.util.Utils; /** * The main fragment that powers the ImageGridActivity screen. Fairly straight * forward GridView implementation with the key addition being the ImageWorker * class w/ImageCache to load children asynchronously, keeping the UI nice and * smooth and caching thumbnails for quick retrieval. The cache is retained over * configuration changes like orientation change so the images are populated * quickly as the user rotates the device. */ public class ImageGridFragment extends Fragment implements AdapterView.OnItemClickListener { private static final String TAG = "ImageGridFragment"; private static final String IMAGE_CACHE_DIR = "thumbs"; private int mImageThumbSize; private int mImageThumbSpacing; private ImageAdapter mAdapter; private ImageResizer mImageWorker; /** * Empty constructor as per the Fragment documentation */ public ImageGridFragment() { } @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setHasOptionsMenu(true); mImageThumbSize = getResources().getDimensionPixelSize(R.dimen.image_thumbnail_size); mImageThumbSpacing = getResources().getDimensionPixelSize(R.dimen.image_thumbnail_spacing); mAdapter = new ImageAdapter(getActivity()); ImageCacheParams cacheParams = new ImageCacheParams(IMAGE_CACHE_DIR); // Allocate a third of the per-app memory limit to the bitmap memory cache. // This value // should be chosen carefully based on a number of factors. Refer to the // corresponding // Android Training class for more discussion: // http://developer.android.com/training/displaying-bitmaps/ // In this case, we aren't using memory for much else other than this // activity and the // ImageDetailActivity so a third lets us keep all our sample image // thumbnails in memory // at once. cacheParams.memCacheSize = 1024 * 1024 * Utils.getMemoryClass(getActivity()) / 3; // The ImageWorker takes care of loading images into our ImageView children // asynchronously mImageWorker = new ImageFetcher(getActivity(), mImageThumbSize); mImageWorker.setAdapter(Images.imageThumbWorkerUrlsAdapter); mImageWorker.setLoadingImage(R.drawable.empty_photo); mImageWorker.setImageCache(ImageCache.findOrCreateCache(getActivity(), cacheParams)); } @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { final View v = inflater.inflate(R.layout.image_grid_fragment, container, false); final GridView mGridView = (GridView) v.findViewById(R.id.gridView); mGridView.setAdapter(mAdapter); mGridView.setOnItemClickListener(this); // This listener is used to get the final width of the GridView and then // calculate the // number of columns and the width of each column. The width of each column // is variable // as the GridView has stretchMode=columnWidth. The column width is used to // set the height // of each view so we get nice square thumbnails. mGridView.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() { @Override public void onGlobalLayout() { if (mAdapter.getNumColumns() == 0) { final int numColumns = (int) Math .floor(mGridView.getWidth() / (mImageThumbSize + mImageThumbSpacing)); if (numColumns > 0) { final int columnWidth = (mGridView.getWidth() / numColumns) - mImageThumbSpacing; mAdapter.setNumColumns(numColumns); mAdapter.setItemHeight(columnWidth); if (BuildConfig.DEBUG) { Log.d(TAG, "onCreateView - numColumns set to " + numColumns); } } } } }); return v; } @Override public void onResume() { super.onResume(); mImageWorker.setExitTasksEarly(false); mAdapter.notifyDataSetChanged(); } @Override public void onPause() { super.onPause(); mImageWorker.setExitTasksEarly(true); } @Override public void onItemClick(AdapterView<?> parent, View v, int position, long id) { final Intent i = new Intent(getActivity(), ImageDetailActivity.class); i.putExtra(ImageDetailActivity.EXTRA_IMAGE, (int) id); startActivity(i); } @Override public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) { inflater.inflate(R.menu.main_menu, menu); } @Override public boolean onOptionsItemSelected(MenuItem item) { switch (item.getItemId()) { case R.id.clear_cache: final ImageCache cache = mImageWorker.getImageCache(); if (cache != null) { mImageWorker.getImageCache().clearCaches(); // DiskLruCache.clearCache(getActivity(), ImageFetcher.HTTP_CACHE_DIR); Toast.makeText(getActivity(), R.string.clear_cache_complete, Toast.LENGTH_SHORT).show(); } return true; } return super.onOptionsItemSelected(item); } /** * The main adapter that backs the GridView. This is fairly standard except * the number of columns in the GridView is used to create a fake top row of * empty views as we use a transparent ActionBar and don't want the real top * row of images to start off covered by it. */ private class ImageAdapter extends BaseAdapter { private final Context mContext; private int mItemHeight = 0; private int mNumColumns = 0; private int mActionBarHeight = -1; private GridView.LayoutParams mImageViewLayoutParams; public ImageAdapter(Context context) { super(); mContext = context; mImageViewLayoutParams = new GridView.LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT); } @Override public int getCount() { // Size of adapter + number of columns for top empty row return mImageWorker.getAdapter().getSize() + mNumColumns; } @Override public Object getItem(int position) { return position < mNumColumns ? null : mImageWorker.getAdapter().getItem(position - mNumColumns); } @Override public long getItemId(int position) { return position < mNumColumns ? 0 : position - mNumColumns; } @Override public int getViewTypeCount() { // Two types of views, the normal ImageView and the top row of empty views return 2; } @Override public int getItemViewType(int position) { return (position < mNumColumns) ? 1 : 0; } @Override public boolean hasStableIds() { return true; } @Override public View getView(int position, View convertView, ViewGroup container) { // First check if this is the top row if (position < mNumColumns) { if (convertView == null) { convertView = new View(mContext); } // Calculate ActionBar height if (mActionBarHeight < 0) { TypedValue tv = new TypedValue(); if (mContext.getTheme().resolveAttribute(android.R.attr.actionBarSize, tv, true)) { mActionBarHeight = TypedValue.complexToDimensionPixelSize(tv.data, mContext.getResources().getDisplayMetrics()); } else { // No ActionBar style (pre-Honeycomb or ActionBar not in theme) mActionBarHeight = 0; } } // Set empty view with height of ActionBar convertView.setLayoutParams( new AbsListView.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, mActionBarHeight)); return convertView; } // Now handle the main ImageView thumbnails ImageView imageView; if (convertView == null) { // if it's not recycled, instantiate and // initialize imageView = new ImageView(mContext); imageView.setScaleType(ImageView.ScaleType.CENTER_CROP); imageView.setLayoutParams(mImageViewLayoutParams); } else { // Otherwise re-use the converted view imageView = (ImageView) convertView; } // Check the height matches our calculated column width if (imageView.getLayoutParams().height != mItemHeight) { imageView.setLayoutParams(mImageViewLayoutParams); } // Finally load the image asynchronously into the ImageView, this also // takes care of // setting a placeholder image while the background thread runs mImageWorker.loadImage(position - mNumColumns, imageView); return imageView; } /** * Sets the item height. Useful for when we know the column width so the * height can be set to match. * * @param height */ public void setItemHeight(int height) { if (height == mItemHeight) { return; } mItemHeight = height; mImageViewLayoutParams = new GridView.LayoutParams(LayoutParams.MATCH_PARENT, mItemHeight); mImageWorker.setImageSize(height); notifyDataSetChanged(); } public void setNumColumns(int numColumns) { mNumColumns = numColumns; } public int getNumColumns() { return mNumColumns; } } }