我试图在Fragment类中获取我的mImageView的位图。 我注意到我可以看到正确的drawable,但有时只创建位图,而大多数情况下都是Null。 这是代码:
package com.example.android.displayingbitmaps.ui;
import android.graphics.Bitmap;
import android.graphics.drawable.BitmapDrawable;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.Toast;
import com.example.android.displayingbitmaps.R;
import com.example.android.displayingbitmaps.util.ImageFetcher;
import com.example.android.displayingbitmaps.util.ImageWorker;
import com.example.android.displayingbitmaps.util.Utils;
/**
* This fragment will populate the children of the ViewPager from {@link ImageDetailActivity}.
*/
public class ImageDetailFragment extends Fragment {
private static final String IMAGE_DATA_EXTRA = "extra_image_data";
private String mImageUrl;
private ImageView mImageView;
private ImageFetcher mImageFetcher;
/**
* Factory method to generate a new instance of the fragment given an image number.
*
* @param imageUrl The image url to load
* @return A new instance of ImageDetailFragment with imageNum extras
*/
public static ImageDetailFragment newInstance(String imageUrl) {
final ImageDetailFragment f = new ImageDetailFragment();
final Bundle args = new Bundle();
args.putString(IMAGE_DATA_EXTRA, imageUrl);
f.setArguments(args);
return f;
}
/**
* Empty constructor as per the Fragment documentation
*/
public ImageDetailFragment() {}
/**
* Populate image using a url from extras, use the convenience factory method
* {@link ImageDetailFragment#newInstance(String)} to create this fragment.
*/
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mImageUrl = getArguments() != null ? getArguments().getString(IMAGE_DATA_EXTRA) : null;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate and locate the main ImageView
final View v = inflater.inflate(R.layout.image_detail_fragment, container, false);
mImageView = (ImageView) v.findViewById(R.id.imageView);
return v;
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
// Use the parent activity to load the image asynchronously into the ImageView (so a single
// cache can be used over all pages in the ViewPager
if (ImageDetailActivity.class.isInstance(getActivity())) {
mImageFetcher = ((ImageDetailActivity) getActivity()).getImageFetcher();
mImageFetcher.loadImage(mImageUrl, mImageView);
BitmapDrawable drawable = (BitmapDrawable) mImageView.getDrawable();
Bitmap bitmap = drawable.getBitmap();
Toast.makeText(getActivity(), "Drawable is: "+drawable,Toast.LENGTH_SHORT).show(); }
// Pass clicks on the ImageView to the parent activity to handle
if (OnClickListener.class.isInstance(getActivity()) && Utils.hasHoneycomb()) {
mImageView.setOnClickListener((OnClickListener) getActivity());
}
}
@Override
public void onDestroy() {
super.onDestroy();
if (mImageView != null) {
// Cancel any pending image work
ImageWorker.cancelWork(mImageView);
mImageView.setImageDrawable(null);
}
}
}
FragmentActivity类
import android.annotation.TargetApi;
import android.app.ActionBar;
import android.os.Build.VERSION_CODES;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;
import android.support.v4.app.NavUtils;
import android.support.v4.view.ViewPager;
import android.util.DisplayMetrics;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.WindowManager.LayoutParams;
import android.widget.ImageView;
import android.widget.Toast;
import com.example.android.displayingbitmaps.BuildConfig;
import com.example.android.displayingbitmaps.R;
import com.example.android.displayingbitmaps.provider.Images;
import com.example.android.displayingbitmaps.util.ImageCache;
import com.example.android.displayingbitmaps.util.ImageFetcher;
import com.example.android.displayingbitmaps.util.Utils;
public class ImageDetailActivity extends FragmentActivity implements OnClickListener {
private static final String IMAGE_CACHE_DIR = "images";
public static final String EXTRA_IMAGE = "extra_image";
private ImagePagerAdapter mAdapter;
private ImageFetcher mImageFetcher;
private ViewPager mPager;
private ImageView mImageView;
@TargetApi(VERSION_CODES.HONEYCOMB)
@Override
public void onCreate(Bundle savedInstanceState) {
if (BuildConfig.DEBUG) {
Utils.enableStrictMode();
}
super.onCreate(savedInstanceState);
setContentView(R.layout.image_detail_pager);
// Fetch screen height and width, to use as our max size when loading images as this
// activity runs full screen
final DisplayMetrics displayMetrics = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
final int height = displayMetrics.heightPixels;
final int width = displayMetrics.widthPixels;
// For this sample we'll use half of the longest width to resize our images. As the
// image scaling ensures the image is larger than this, we should be left with a
// resolution that is appropriate for both portrait and landscape. For best image quality
// we shouldn't divide by 2, but this will use more memory and require a larger memory
// cache.
final int longest = (height > width ? height : width) / 2;
ImageCache.ImageCacheParams cacheParams =
new ImageCache.ImageCacheParams(this, IMAGE_CACHE_DIR);
cacheParams.setMemCacheSizePercent(0.25f); // Set memory cache to 25% of app memory
// The ImageFetcher takes care of loading images into our ImageView children asynchronously
mImageFetcher = new ImageFetcher(this, longest);
mImageFetcher.addImageCache(getSupportFragmentManager(), cacheParams);
mImageFetcher.setImageFadeIn(false);
// Set up ViewPager and backing adapter
mAdapter = new ImagePagerAdapter(getSupportFragmentManager(), Images.imageUrls.length);
mPager = (ViewPager) findViewById(R.id.pager);
mPager.setAdapter(mAdapter);
mPager.setPageMargin((int) getResources().getDimension(R.dimen.horizontal_page_margin));
mPager.setOffscreenPageLimit(2);
// Set up activity to go full screen
getWindow().addFlags(LayoutParams.FLAG_FULLSCREEN);
// Enable some additional newer visibility and ActionBar features to create a more
// immersive photo viewing experience
if (Utils.hasHoneycomb()) {
final ActionBar actionBar = getActionBar();
// Hide title text and set home as up
actionBar.setDisplayShowTitleEnabled(false);
actionBar.setDisplayHomeAsUpEnabled(true);
// Hide and show the ActionBar as the visibility changes
mPager.setOnSystemUiVisibilityChangeListener(
new View.OnSystemUiVisibilityChangeListener() {
@Override
public void onSystemUiVisibilityChange(int vis) {
if ((vis & View.SYSTEM_UI_FLAG_LOW_PROFILE) != 0) {
actionBar.hide();
} else {
actionBar.show();
}
}
});
// Start low profile mode and hide ActionBar
mPager.setSystemUiVisibility(View.SYSTEM_UI_FLAG_LOW_PROFILE);
actionBar.hide();
}
// Set the current item based on the extra passed in to this activity
final int extraCurrentItem = getIntent().getIntExtra(EXTRA_IMAGE, -1);
if (extraCurrentItem != -1) {
mPager.setCurrentItem(extraCurrentItem);
}
}
@Override
public void onResume() {
super.onResume();
mImageFetcher.setExitTasksEarly(false);
}
@Override
protected void onPause() {
super.onPause();
mImageFetcher.setExitTasksEarly(true);
mImageFetcher.flushCache();
}
@Override
protected void onDestroy() {
super.onDestroy();
mImageFetcher.closeCache();
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
NavUtils.navigateUpFromSameTask(this);
return true;
case R.id.clear_cache:
mImageFetcher.clearCache();
Toast.makeText(
this, R.string.clear_cache_complete_toast,Toast.LENGTH_SHORT).show();
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main_menu, menu);
return true;
}
/**
* Called by the ViewPager child fragments to load images via the one ImageFetcher
*/
public ImageFetcher getImageFetcher() {
return mImageFetcher;
}
/**
* The main adapter that backs the ViewPager. A subclass of FragmentStatePagerAdapter as there
* could be a large number of items in the ViewPager and we don't want to retain them all in
* memory at once but create/destroy them on the fly.
*/
private class ImagePagerAdapter extends FragmentStatePagerAdapter {
private final int mSize;
public ImagePagerAdapter(FragmentManager fm, int size) {
super(fm);
mSize = size;
}
@Override
public int getCount() {
return mSize;
}
@Override
public Fragment getItem(int position) {
return ImageDetailFragment.newInstance(Images.imageUrls[position]);
}
}
/**
* Set on the ImageView in the ViewPager children fragments, to enable/disable low profile mode
* when the ImageView is touched.
*/
@TargetApi(VERSION_CODES.HONEYCOMB)
@Override
public void onClick(View v) {
final int vis = mPager.getSystemUiVisibility();
//Toast.makeText(this, "Value is: " + ,Toast.LENGTH_SHORT).show();
if ((vis & View.SYSTEM_UI_FLAG_LOW_PROFILE) != 0) {
mPager.setSystemUiVisibility(View.SYSTEM_UI_FLAG_VISIBLE);
} else {
mPager.setSystemUiVisibility(View.SYSTEM_UI_FLAG_LOW_PROFILE);
}
}
}
正如你所看到的,我放了一个向我展示的Toast: 当Toast是Drawable时:
当Toast是Bitmap时,有时会为同一个图像显示位图null(因为我在画廊中向后和向前滑动):
同一图像上的位图不为空:
我正在使用Android M 6.0的AVD图像