我是 Java 和 Android 开发的新手。我试图从谷歌图像下载 jpg 图像并在网格中显示它们,但 BitmapFactory.decode 总是返回 null。我在 Mac 上工作,但没有成功启动 avd 来检查下载的文件(我无法访问带有 ADT 的设备上的文件层次结构......我猜它只适用于 AVD)。我检查了不下载 CMJN 图像,我检查了文件是否下载成功但没有成功...
这是完整的代码......任何帮助表示赞赏:)
Android 清单
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.test.downloadjpgtest"
android:versionCode="1"
android:versionName="1.0" >
<uses-permission android:name="android.permission.INTERNET" />
<uses-sdk
android:minSdkVersion="15"
android:targetSdkVersion="16" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.test.downloadjpgtest.Main"
android:label="@string/title_activity_main" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
资源/布局/activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<GridView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/gridview"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:columnWidth="90dp"
android:numColumns="auto_fit"
android:verticalSpacing="10dp"
android:horizontalSpacing="10dp"
android:stretchMode="columnWidth"
android:gravity="center"
/>
com.test.downloadjpgtest/Main.java
package com.test.downloadjpgtest;
import java.io.File;
import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.support.v4.app.NavUtils;
import android.util.Log;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.Toast;
public class Main extends Activity {
GridView gridview;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// GetLibraryTask
DownloadTask downloadTask = new DownloadTask(this);
downloadTask.execute("http://sphotos-b.xx.fbcdn.net/hphotos-ash4/c0.0.400.400/p403x403/382050_498705510162306_1891776516_n.jpg",
"http://data.alipson.fr/ravensburger.17/ravensburger-puzzle-1000-pieces-panoramique-amitie-entre-animaux-.44481-1.jpg",
"http://a388.idata.over-blog.com/400x400/3/03/14/36/mammiferes/lynx-canada-04.jpg",
"http://photos.ugal.com/6353/43314/205322/246370/vignette-chapeaux-animaux.400.jpg"
);
// grille des couvertures
gridview = (GridView) findViewById(R.id.gridview);
}
// called well all downloads finished
public void setGridAdapter(){
gridview.setAdapter(new ImageAdapter(this));
gridview.setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View v, int position, long id) {
Toast.makeText(Main.this, "" + position, Toast.LENGTH_SHORT).show();
}
});
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
NavUtils.navigateUpFromSameTask(this);
return true;
}
return super.onOptionsItemSelected(item);
}
public class ImageAdapter extends BaseAdapter {
private Context mContext;
public Bitmap[] imgs;
public ImageAdapter(Context c) {
mContext = c;
get_images();
}
public int getCount() {
return imgs.length;
}
public Object getItem(int position) {
return imgs[position];
}
public long getItemId(int position) {
return 0;
}
// create a new ImageView for each item referenced by the Adapter
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(85, 85));
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
imageView.setPadding(8, 8, 8, 8);
} else {
imageView = (ImageView) convertView;
}
imageView.setImageBitmap(imgs[position]);
return imageView;
}
private void get_images(){
File directory = mContext.getDir("jpgfolder", Context.MODE_PRIVATE);
File[] filesInJPGFolder = directory.listFiles();
imgs = new Bitmap[filesInJPGFolder.length];
for (int cpt=0; cpt<filesInJPGFolder.length;cpt++){
File imgFile = new File(filesInJPGFolder[cpt].toString());
imgs[cpt] = BitmapFactory.decodeFile(imgFile.getAbsolutePath()); // imgs[cpt] Always Null !!!!!!!!!
Log.d("Main", "imgCovers[cpt] " + imgs[cpt]);
}
}
}
}
com.test.downloadjpgtest/DownloadTask.java
package com.test.downloadjpgtest;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;
import org.apache.http.client.ClientProtocolException;
import android.app.Activity;
import android.content.Context;
import android.content.ContextWrapper;
import android.os.AsyncTask;
import android.util.Log;
public class DownloadTask extends AsyncTask<String, Void, String> {
private Activity activity;
private static final int files2Download = 4;
private static int filesDownloaded = 0;
public DownloadTask(Activity activity){
this.activity = activity;
}
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected String doInBackground(String... args) {
this.saveFileOnDisk(args[0], "1.jpg");
this.saveFileOnDisk(args[1], "2.jpg");
this.saveFileOnDisk(args[2], "3.jpg");
this.saveFileOnDisk(args[3], "4.jpg");
return "ok"; // just to return a string
}
protected String saveFileOnDisk(String urlString, String outputName){
try {
// in
URL url = new URL(urlString);
InputStream input = url.openConnection().getInputStream();
// out
ContextWrapper contextWrapper = new ContextWrapper(activity.getApplicationContext());
File directory = contextWrapper.getDir("jpgfolder", Context.MODE_PRIVATE);
File newFile = new File(directory, outputName);
newFile.createNewFile();
FileOutputStream fos = this.activity.getApplicationContext().openFileOutput(outputName, Context.MODE_PRIVATE);
int read;
byte[] data = new byte[1024];
while ((read = input.read(data)) != -1)
fos.write(data, 0, read);
fos.close();
DownloadTask.filesDownloaded++;
return newFile.getAbsolutePath();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return "ko";
}
protected void onProgressUpdate(String... progress) {
Log.i("progress", progress[0]);
}
@Override
protected void onPostExecute(String result) {
try {
Log.d("DownloadTask", "All downloads finished");
// check downloaded files
ContextWrapper contextWrapper = new ContextWrapper(activity.getApplicationContext());
File directory = contextWrapper.getDir("jpgfolder", Context.MODE_PRIVATE);
File[] filesInDirectory = directory.listFiles();
for(int i=0, max = filesInDirectory.length; i < max; i++){
Log.i("DownloadTask", "file " + i + " > " + filesInDirectory[i] + " exist?" + filesInDirectory[i].exists());
}
// set grid adapter ... cf Main.java
((Main) this.activity).setGridAdapter();
} catch (Exception e) {
e.printStackTrace();
}
}
}