Android 帮助在没有互联网连接时停止活动崩溃 (FC)

Question

我已经按照教程远程下载图像，当存在互联网连接时它工作正常，但是当您在没有互联网连接的情况下启动活动时，活动崩溃“强制关闭”，

不幸的是，我是一个 Android 新手，所以我不是确定如何阻止它崩溃。他们是用空白屏幕来庆祝一条消息“抱歉，需要互联网”的一种方式，没什么花哨的，只是为了阻止它崩溃。

希望有人能告诉我如何做到这一点 谢谢 露西

private ImageAdapter imageAdapter;

private ArrayList<String> PhotoURLS = new ArrayList<String>();

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    this.requestWindowFeature(Window.FEATURE_NO_TITLE);
      this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN ,
            WindowManager.LayoutParams.FLAG_FULLSCREEN );

    setContentView(R.layout.galleryview);

    public static boolean isDataConnectionAvailable(Context context){
        ConnectivityManager connectivityManager = (ConnectivityManager)context.getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo info = connectivityManager.getActiveNetworkInfo();
        if(info == null)
            return false;

        return connectivityManager.getActiveNetworkInfo().isConnected();
    }

    imageAdapter = new ImageAdapter(this);
    final ImageView imgView = (ImageView) findViewById(R.id.GalleryView);
    Gallery g = (Gallery) findViewById(R.id.Gallery);
    g.setAdapter(imageAdapter);
    g.setOnItemClickListener(new OnItemClickListener() {
        public void onItemClick(AdapterView<?> parent, View v,
                int position, long id) {
            imgView.setImageDrawable(LoadImageFromURL(PhotoURLS
                    .get(position)));
            imgView.setScaleType(ImageView.ScaleType.FIT_XY);
        }
    });

    // replace this code to set your image urls in list
    PhotoURLS.add("http://domain.com/image-286.jpg"); 
    PhotoURLS.add("http://domain.com/image-285.jpg"); 
    PhotoURLS.add("http://domain.com/image-284.jpg"); 
    PhotoURLS.add("http://domain.com/image-283.jpg"); 
    PhotoURLS.add("http://domain.com/image-282.jpg"); 
    PhotoURLS.add("http://domain.com/image-281.jpg"); 


    new AddImageTask().execute();

}

class AddImageTask extends AsyncTask<Void, Void, Void> {
    @Override
    protected Void doInBackground(Void... unused) {
        for (String url : PhotoURLS) {
            String filename = url.substring(url.lastIndexOf("/") + 1,
                    url.length());
            filename = "th_" + filename;
            String thumburl = url.substring(0, url.lastIndexOf("/") + 1);
            imageAdapter.addItem(LoadThumbnailFromURL(thumburl + filename));
            publishProgress();
            //SystemClock.sleep(200);
        }

        return (null);
    }

    @Override
    protected void onProgressUpdate(Void... unused) {
        imageAdapter.notifyDataSetChanged();
    }

    @Override
    protected void onPostExecute(Void unused) {
    }
}

private Drawable LoadThumbnailFromURL(String url) {
    try {
        URLConnection connection = new URL(url).openConnection();
        String contentType = connection.getHeaderField("Content-Type");
        boolean isImage = contentType.startsWith("image/");
        if(isImage){
            HttpGet httpRequest = new HttpGet(url);
            HttpClient httpclient = new DefaultHttpClient();
            HttpResponse response = (HttpResponse) httpclient
                    .execute(httpRequest);
            HttpEntity entity = response.getEntity();
            BufferedHttpEntity bufferedHttpEntity = new BufferedHttpEntity(entity);

            InputStream is = bufferedHttpEntity.getContent();
            Drawable d = Drawable.createFromStream(is, "src Name");
            return d;
        } else {
            Bitmap b = BitmapFactory.decodeResource(getResources(), R.drawable.no_image);
            Drawable d = new BitmapDrawable(b);
            return d;
        }
    } catch (Exception e) {
        Toast.makeText(getApplicationContext(), "error", Toast.LENGTH_LONG)
                .show();
        Log.e(e.getClass().getName(), e.getMessage(), e);
        return null;
    }
}

private Drawable LoadImageFromURL(String url) {
    try {
        URLConnection connection = new URL(url).openConnection();
        String contentType = connection.getHeaderField("Content-Type");
        boolean isImage = contentType.startsWith("image/");
        if(isImage){
            HttpGet httpRequest = new HttpGet(url);
            HttpClient httpclient = new DefaultHttpClient();
            HttpResponse response = (HttpResponse) httpclient
                    .execute(httpRequest);
            HttpEntity entity = response.getEntity();
            BufferedHttpEntity bufferedHttpEntity = new BufferedHttpEntity(
                    entity);
            InputStream is = bufferedHttpEntity.getContent();

            // Decode image size
            BitmapFactory.Options o = new BitmapFactory.Options();
            o.inJustDecodeBounds = true;
            BitmapFactory.decodeStream(is, null, o);

            // The new size we want to scale to
            final int REQUIRED_SIZE = 320;

            // Find the correct scale value. It should be the power of 2.
            int width_tmp = o.outWidth, height_tmp = o.outHeight;
            int scale = 1;
            while (true) {
                if (width_tmp / 2 < REQUIRED_SIZE
                        || height_tmp / 2 < REQUIRED_SIZE)
                    break;
                width_tmp /= 2;
                height_tmp /= 2;
                scale *= 2;
            }

            // Decode with inSampleSize
            is = bufferedHttpEntity.getContent();
            BitmapFactory.Options o2 = new BitmapFactory.Options();
            o2.inSampleSize = scale;
            Bitmap b = BitmapFactory.decodeStream(is, null, o2);
            Drawable d = new BitmapDrawable(b);
            return d;
        } else {
            Bitmap b = BitmapFactory.decodeResource(getResources(), R.drawable.no_image);
            Drawable d = new BitmapDrawable(b);
            return d;
        }
    } catch (Exception e) {
        Toast.makeText(getApplicationContext(), "error", Toast.LENGTH_LONG)
                .show();
        Log.e(e.getClass().getName(), e.getMessage(), e);
        return null;
    }
}

public class ImageAdapter extends BaseAdapter {
    int mGalleryItemBackground;
    private Context mContext;

    ArrayList<Drawable> drawablesFromUrl = new ArrayList<Drawable>();

    public ImageAdapter(Context c) {
        mContext = c;
        TypedArray a = obtainStyledAttributes(R.styleable.GalleryTheme);
        mGalleryItemBackground = a.getResourceId(
        R.styleable.GalleryTheme_android_galleryItemBackground, 0);
        a.recycle();
    }

    public void addItem(Drawable item) {
        drawablesFromUrl.add(item);
    }

    public int getCount() {
        return drawablesFromUrl.size();
    }

    public Drawable getItem(int position) {
        return drawablesFromUrl.get(position);
    }

    public long getItemId(int position) {
        return position;
    }

    public View getView(int position, View convertView, ViewGroup parent) {
        ImageView i = new ImageView(mContext);

        i.setImageDrawable(drawablesFromUrl.get(position));
        i.setLayoutParams(new Gallery.LayoutParams(70, 110));
        i.setScaleType(ImageView.ScaleType.FIT_CENTER);
        //i.setBackgroundResource(mGalleryItemBackground);

        return i;


    }


}

}

Answer 1

您可以检查连接可用性：

public static boolean isDataConnectionAvailable(Context context){
        ConnectivityManager connectivityManager = (ConnectivityManager)context.getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo info = connectivityManager.getActiveNetworkInfo();
        if(info == null)
            return false;

        return connectivityManager.getActiveNetworkInfo().isConnected();
    }

注意：向清单文件添加权限：

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

Answer 2

我可以确认 Vineet 的回答很好，因为我也遇到了同样的问题。

我的代码不起作用如下：

public boolean isOnline() {

final ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);        
final NetworkInfo networkInfo = cm.getActiveNetworkInfo();      
boolean connected = networkInfo.isConnected();

    if (connected)
        return true;
    else
        return false;

}

我上面的示例的问题是 networkInfo.isConnected() 似乎没有值。我将一个布尔值设置为 null，我认为这是不允许的（是的，我的 Java 很粗略，因为我是新手），因此应用程序会抛出异常并崩溃。

现在我使用 Vineet 的解决方案解决了这个问题。

public boolean isOnline() {

final ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);        
final NetworkInfo networkInfo = cm.getActiveNetworkInfo();      

if(networkInfo == null)
    return false;
else
    return networkInfo.isConnected();

现在

，它可以正常工作并且应用程序不再崩溃。希望这个解决方案可以帮助某人。我怀疑 JAVA 大师将能够更好地解释不允许将 boolean 设置为 Null 的问题。