好吧，我一直在为Android制作一个Gallery App。我已经使用ViewHolder来防止滚动时出现延迟。但是，当我向上滚动时，上面的图像被其他图像替换。过了一会儿，原始图像显示在网格中。为什么会这样？另外，我该如何解决这个问题？
另一个问题，其他图库应用如何显示图像？他们也使用ViewHolder吗？
任何帮助都将受到高度赞赏。
这是我的MainActivity类：
package com.example.om.imageviewer3;
import java.io.File;
import java.util.ArrayList;
import java.util.Arrays;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Environment;
import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.Toast;
public class MainActivity extends Activity {
AsyncTaskLoadFiles myAsyncTaskLoadFiles;
public class AsyncTaskLoadFiles extends AsyncTask<Void, String, Void> {
File targetDirector;
ImageAdapter myTaskAdapter;
public AsyncTaskLoadFiles(ImageAdapter adapter) {
myTaskAdapter = adapter;
}
@Override
protected void onPreExecute() {
String ExternalStorageDirectoryPath = Environment
.getExternalStorageDirectory().getAbsolutePath();
String targetPath = ExternalStorageDirectoryPath + "/DCIM/Camera/";
targetDirector = new File(targetPath);
myTaskAdapter.clear();
super.onPreExecute();
}
@Override
protected Void doInBackground(Void... params) {
File[] files = targetDirector.listFiles();
Arrays.sort(files);
for (File file : files) {
publishProgress(file.getAbsolutePath());
if (isCancelled()) break;
}
return null;
}
@Override
protected void onProgressUpdate(String... values) {
myTaskAdapter.add(values[0]);
super.onProgressUpdate(values);
}
@Override
protected void onPostExecute(Void result) {
myTaskAdapter.notifyDataSetChanged();
super.onPostExecute(result);
}
}
public class ImageAdapter extends BaseAdapter {
private Context mContext;
ArrayList<String> itemList = new ArrayList<String>();
public ImageAdapter(Context c) {
mContext = c;
}
void add(String path) {
itemList.add(path);
}
void clear() {
itemList.clear();
}
void remove(int index){
itemList.remove(index);
}
@Override
public int getCount() {
return itemList.size();
}
@Override
public Object getItem(int position) {
// TODO Auto-generated method stub
return itemList.get(position);
}
@Override
public long getItemId(int position) {
// TODO Auto-generated method stub
return 0;
}
//getView load bitmap ui thread
/*
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ImageView imageView;
if (convertView == null) { // if it's not recycled, initialize some
// attributes
imageView = new ImageView(mContext);
imageView.setLayoutParams(new GridView.LayoutParams(220, 220));
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
imageView.setPadding(8, 8, 8, 8);
} else {
imageView = (ImageView) convertView;
}
Bitmap bm = decodeSampledBitmapFromUri(itemList.get(position), 220,
220);
imageView.setImageBitmap(bm);
return imageView;
}
*/
//getView load bitmap in AsyncTask
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
ViewHolder holder;
ImageView imageView;
if (convertView == null) { // if it's not recycled, initialize some
// attributes
imageView = new ImageView(mContext);
imageView.setLayoutParams(new GridView.LayoutParams(220,250));
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
imageView.setPadding(8, 8, 8, 8);
convertView = imageView;
holder = new ViewHolder();
holder.image = imageView;
holder.position = position;
convertView.setTag(holder);
} else {
//imageView = (ImageView) convertView;
holder = (ViewHolder) convertView.getTag();
((ImageView)convertView).setImageBitmap(null);
}
//Bitmap bm = decodeSampledBitmapFromUri(itemList.get(position), 220, 220);
// Using an AsyncTask to load the slow images in a background thread
new AsyncTask<ViewHolder, Void, Bitmap>() {
private ViewHolder v;
@Override
protected Bitmap doInBackground(ViewHolder... params) {
v = params[0];
Bitmap bm = decodeSampledBitmapFromUri(itemList.get(position), 500, 500);
return bm;
}
@Override
protected void onPostExecute(Bitmap result) {
super.onPostExecute(result);
//Not work for me!
/*
if (v.position == position) {
// If this item hasn't been recycled already,
// show the image
v.image.setImageBitmap(result);
}
*/
v.image.setImageBitmap(result);
}
}.execute(holder);
//imageView.setImageBitmap(bm);
//return imageView;
return convertView;
}
public Bitmap decodeSampledBitmapFromUri(String path, int reqWidth,
int reqHeight) {
Bitmap bm = null;
// First decode with inJustDecodeBounds=true to check dimensions
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFile(path, options);
// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth,
reqHeight);
// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;
bm = BitmapFactory.decodeFile(path, options);
return bm;
}
public int calculateInSampleSize(
BitmapFactory.Options options, int reqWidth, int reqHeight) {
// Raw height and width of image
final int height = options.outHeight;
final int width = options.outWidth;
int inSampleSize = 1;
if (height > reqHeight || width > reqWidth) {
if (width > height) {
inSampleSize = Math.round((float) height
/ (float) reqHeight);
} else {
inSampleSize = Math.round((float) width / (float) reqWidth);
}
}
return inSampleSize;
}
class ViewHolder {
ImageView image;
int position;
}
}
ImageAdapter myImageAdapter;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final GridView gridview = (GridView) findViewById(R.id.gridview);
myImageAdapter = new ImageAdapter(this);
gridview.setAdapter(myImageAdapter);
/*
* Move to asyncTaskLoadFiles String ExternalStorageDirectoryPath =
* Environment .getExternalStorageDirectory() .getAbsolutePath();
*
* String targetPath = ExternalStorageDirectoryPath + "/test/";
*
* Toast.makeText(getApplicationContext(), targetPath,
* Toast.LENGTH_LONG).show(); File targetDirector = new
* File(targetPath);
*
* File[] files = targetDirector.listFiles(); for (File file : files){
* myImageAdapter.add(file.getAbsolutePath()); }
*/
myAsyncTaskLoadFiles = new AsyncTaskLoadFiles(myImageAdapter);
myAsyncTaskLoadFiles.execute();
gridview.setOnItemClickListener(myOnItemClickListener);
Button buttonReload = (Button)findViewById(R.id.reload);
buttonReload.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View arg0) {
//Cancel the previous running task, if exist.
myAsyncTaskLoadFiles.cancel(true);
//new another ImageAdapter, to prevent the adapter have
//mixed files
myImageAdapter = new ImageAdapter(MainActivity.this);
gridview.setAdapter(myImageAdapter);
myAsyncTaskLoadFiles = new AsyncTaskLoadFiles(myImageAdapter);
myAsyncTaskLoadFiles.execute();
}});
}
OnItemClickListener myOnItemClickListener = new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position,
long id) {
String prompt = "remove " + (String) parent.getItemAtPosition(position);
Toast.makeText(getApplicationContext(), prompt, Toast.LENGTH_SHORT)
.show();
myImageAdapter.remove(position);
myImageAdapter.notifyDataSetChanged();
}
};
}
更新：这里是代码（它很多）
package com.example.om.imageviewer4;
import java.io.File;
import java.util.ArrayList;
import java.util.Arrays;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Environment;
import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.Toast;
public class MainActivity extends Activity {
AsyncTaskLoadFiles myAsyncTaskLoadFiles;
public class AsyncTaskLoadFiles extends AsyncTask<Void, String, Void> {
File targetDirector;
ImageAdapter myTaskAdapter;
public AsyncTaskLoadFiles(ImageAdapter adapter) {
myTaskAdapter = adapter;
}
@Override
protected void onPreExecute() {
String ExternalStorageDirectoryPath = Environment
.getExternalStorageDirectory().getAbsolutePath();
String targetPath = ExternalStorageDirectoryPath + "/DCIM/Camera/";
targetDirector = new File(targetPath);
myTaskAdapter.clear();
super.onPreExecute();
}
@Override
protected Void doInBackground(Void... params) {
File[] files = targetDirector.listFiles();
Arrays.sort(files);
for (File file : files) {
publishProgress(file.getAbsolutePath());
if (isCancelled()) break;
}
return null;
}
@Override
protected void onProgressUpdate(String... values) {
myTaskAdapter.add(values[0]);
super.onProgressUpdate(values);
}
@Override
protected void onPostExecute(Void result) {
myTaskAdapter.notifyDataSetChanged();
super.onPostExecute(result);
}
}
public class ImageAdapter extends BaseAdapter {
private Context mContext;
ArrayList<String> itemList = new ArrayList<String>();
public ImageAdapter(Context c) {
mContext = c;
}
void add(String path) {
itemList.add(path);
}
void clear() {
itemList.clear();
}
void remove(int index){
itemList.remove(index);
}
@Override
public int getCount() {
return itemList.size();
}
@Override
public Object getItem(int position) {
// TODO Auto-generated method stub
return itemList.get(position);
}
@Override
public long getItemId(int position) {
// TODO Auto-generated method stub
return 0;
}
//getView load bitmap ui thread
/*
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ImageView imageView;
if (convertView == null) { // if it's not recycled, initialize some
// attributes
imageView = new ImageView(mContext);
imageView.setLayoutParams(new GridView.LayoutParams(220, 220));
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
imageView.setPadding(8, 8, 8, 8);
} else {
imageView = (ImageView) convertView;
}
Bitmap bm = decodeSampledBitmapFromUri(itemList.get(position), 220,
220);
imageView.setImageBitmap(bm);
return imageView;
}
*/
//getView load bitmap in AsyncTask
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
final ViewHolder holder;
ImageView imageView;
if (convertView == null) { // if it's not recycled, initialize some
// attributes
imageView = new ImageView(mContext);
imageView.setLayoutParams(new GridView.LayoutParams(220, 220));
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
imageView.setPadding(8, 8, 8, 8);
convertView = imageView;
holder = new ViewHolder();
holder.image = imageView;
holder.position = position;
convertView.setTag(holder);
} else {
//imageView = (ImageView) convertView;
holder = (ViewHolder) convertView.getTag();
holder.position=position;
((ImageView)convertView).setImageBitmap(null);
}
//Bitmap bm = decodeSampledBitmapFromUri(itemList.get(position), 220, 220);
// Using an AsyncTask to load the slow images in a background thread
new AsyncTask<ViewHolder, Void, Bitmap>() {
private ViewHolder v;
private String path=holder.toString();
/*@Override
protected void onPreExecute(){
path=v.image.getTag().toString();
}*/
@Override
protected Bitmap doInBackground(ViewHolder... params) {
v = params[0];
//path=v.image.getTag().toString();
Bitmap bm = decodeSampledBitmapFromUri(itemList.get(position), 220, 220);
return bm;
}
@Override
protected void onPostExecute(Bitmap result) {
super.onPostExecute(result);
//Not work for me!
//Toast.makeText(mContext,"WTF: "+v.image.getTag().toString()+"\n"+holder.image.getTag().toString(),Toast.LENGTH_SHORT).show();
if(!v.image.getTag().toString().equals(path)){
Toast.makeText(mContext,"Here3",Toast.LENGTH_SHORT).show();
return;
}
if(result!=null && v.image!=null && v.position==position){
Toast.makeText(mContext,"HereUP",Toast.LENGTH_SHORT).show();
v.image.setVisibility(View.VISIBLE);
v.image.setImageBitmap(result);
}
else{
Toast.makeText(mContext,"Here",Toast.LENGTH_SHORT).show();
v.image.setVisibility(View.GONE);
}
//v.image.setImageBitmap(result);
}
}.execute(holder);
//imageView.setImageBitmap(bm);
//return imageView;
return convertView;
}
public Bitmap decodeSampledBitmapFromUri(String path, int reqWidth,
int reqHeight) {
Bitmap bm = null;
// First decode with inJustDecodeBounds=true to check dimensions
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFile(path, options);
// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth,
reqHeight);
// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;
bm = BitmapFactory.decodeFile(path, options);
return bm;
}
public int calculateInSampleSize(
BitmapFactory.Options options, int reqWidth, int reqHeight) {
// Raw height and width of image
final int height = options.outHeight;
final int width = options.outWidth;
int inSampleSize = 1;
if (height > reqHeight || width > reqWidth) {
if (width > height) {
inSampleSize = Math.round((float) height
/ (float) reqHeight);
} else {
inSampleSize = Math.round((float) width / (float) reqWidth);
}
}
return inSampleSize;
}
class ViewHolder {
ImageView image;
int position;
}
}
ImageAdapter myImageAdapter;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final GridView gridview = (GridView) findViewById(R.id.gridview);
myImageAdapter = new ImageAdapter(this);
gridview.setAdapter(myImageAdapter);
/*
* Move to asyncTaskLoadFiles String ExternalStorageDirectoryPath =
* Environment .getExternalStorageDirectory() .getAbsolutePath();
*
* String targetPath = ExternalStorageDirectoryPath + "/test/";
*
* Toast.makeText(getApplicationContext(), targetPath,
* Toast.LENGTH_LONG).show(); File targetDirector = new
* File(targetPath);
*
* File[] files = targetDirector.listFiles(); for (File file : files){
* myImageAdapter.add(file.getAbsolutePath()); }
*/
myAsyncTaskLoadFiles = new AsyncTaskLoadFiles(myImageAdapter);
myAsyncTaskLoadFiles.execute();
gridview.setOnItemClickListener(myOnItemClickListener);
}
OnItemClickListener myOnItemClickListener = new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position,
long id) {
String prompt = "remove " + (String) parent.getItemAtPosition(position);
Toast.makeText(getApplicationContext(), prompt, Toast.LENGTH_SHORT)
.show();
myImageAdapter.remove(position);
myImageAdapter.notifyDataSetChanged();
}
};
}
答案 0 :(得分：0)
您肯定需要检查此视图是否已用于其他位置，但您还需要每次在持有者中更改位置。
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
if (convertView == null) {
ImageView imageView = new ImageView(mContext);
imageView.setLayoutParams(new GridView.LayoutParams(220, 250));
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
imageView.setPadding(8, 8, 8, 8);
ViewHolder dataHolder = new ViewHolder();
dataHolder.image = imageView;
imageView.setTag(dataHolder);
convertView = imageView;
}
ViewHolder holder = (ViewHolder) convertView.getTag();
holder.image.setImageBitmap(null);
holder.position = position; // <-- this line
new AsyncTask<ViewHolder, Void, Bitmap>() {
private ViewHolder v;
@Override
protected Bitmap doInBackground(ViewHolder... params) {
v = params[0];
Bitmap bm=decodeSampledBitmapFromUri(itemList.get(position), 500, 500);
return bm;
}
@Override
protected void onPostExecute(Bitmap result) {
if (position == v.position) // <-- this line
v.image.setImageBitmap(result); // <-- this line
}
}.execute(holder);
return convertView;
}