Android开发Tips-1

打算记录一些自己在开发过程中遇到的一些技巧性代码，方便以后遇到相似功能时能够快速的找到，那就从这里开始吧。

1,如何截取当前屏幕(不包括当前Activity的Title)并分享：

a,获取当前Activity的根视图：
  View rootView = getWindow().getDecorView().findViewById(android.R.id.content); 
或者：
  View rootView = findViewById(android.R.id.content); 
或者：
  View rootView = findViewById(android.R.id.content).getRootView(); 
关于android.R.id.content，开发者文档中并没有给予说明，但经过测试它应该是用来获取setContentView()中设置的View。
b,截取当前根视图的屏幕:

 public static Bitmap getScreenShot(View view) {
     View screenView = view.getRootView();
     screenView.setDrawingCacheEnabled(true);
     Bitmap bitmap = Bitmap.createBitmap(screenView.getDrawingCache());
     screenView.setDrawingCacheEnabled(false);
     return bitmap;
 }

getScreenShot

c,将当前屏幕的截屏保存至SDCard:

 private final static String dir = Environment.getExternalStorageDirectory().getAbsolutePath() + "/Screenshots";
 public static void store(Bitmap bm, String fileName){
     File dir = new File(dir);
     if(!dir.exists())
         dir.mkdirs();
     File file = new File(dir, fileName);
     try {
         FileOutputStream fOut = new FileOutputStream(file);
         bm.compress(Bitmap.CompressFormat.PNG, 85, fOut);
         fOut.flush();
         fOut.close();
     } catch (Exception e) {
         e.printStackTrace();
     }
 }

store(Bitmap bm, String fileName)

d,最后将该图片文件分享出来:

 private void shareImage(String file){
     Uri uri = Uri.fromFile(file);
     Intent intent = new Intent();
     intent.setAction(Intent.ACTION_SEND);
     intent.setType("image/*");
     intent.putExtra(android.content.Intent.EXTRA_SUBJECT, "");
     intent.putExtra(android.content.Intent.EXTRA_TEXT, "");
     intent.putExtra(Intent.EXTRA_STREAM, uri);
     startActivity(Intent.createChooser(intent, "Share Screenshot"));
 }

shareImage(String file)

2,如何对HTML5中的视频截图:

a,初始化WebView:

 String webUrl = ...;
 VideoView vv;
 mWebView = (WebView) findViewById(R.id.webview);
 mWebView.setWebChromeClient(chromeClient);
 mWebView.setWebViewClient(wvClient);
 mWebView.getSettings().setJavaScriptEnabled(true);
 mWebView.getSettings().setPluginsEnabled(true);
 mWebView.loadUrl(webUrl);

b,覆盖WebChromeClient中的onShowCustomView方法:

 @Override
 public void onShowCustomView(View view, CustomViewCallback callback) {
     super.onShowCustomView(view, callback);
     if (view instanceof FrameLayout){
         FrameLayout frame = (FrameLayout) view;
         if (frame.getFocusedChild() instanceof VideoView){
             vv = (VideoView) frame.getFocusedChild();
         }
     }
 }

onShowCustomView(View view, CustomViewCallback callback)

c,截取VideoView中播放的视频内容:

 private Bitmap capture(VideoView vv){
     MediaMetadataRetriever rev = new MediaMetadataRetriever();
     rev.setDataSource(this, uri);//this is a Context;
     Bitmap bitmap = rev.getFrameAtTime(vv.getCurrentPosition() * 1000, MediaMetadataRetriever.OPTION_CLOSEST_SYNC);
     return bitmap;
 }

capture(VideoView vv)

d,如何还想将截屏幕保存或分享，请参见上面的代码示例.

3,如何动态获取保存在integer-array中的动态资源id？

a,在res/values/目录下创建arrays.xml文件，创建内容如下:

 <integer-array name="frag_home_ids">
     <item>@drawable/frag_home_credit_return_money</item>
     <item>@drawable/frag_home_transfer</item>
     <item>@drawable/frag_home_balance</item>
     <item>@drawable/frag_home_charge</item>
     <item>@drawable/frag_home_finance_cdd</item>
     <item>@drawable/frag_home_finance_ybjr</item>
     <item>@drawable/frag_home_more</item>
 </integer-array>

arrays.xml

b,通过编码的方式获取integer-array中的资源id整型值:

 TypedArray tArray = getResources().obtainTypedArray(R.array.frag_home_ids);
 int count = tArray.length();
 int[] ids = new int[count];
 for (int i = 0; i < ids.length; i++) {
     ids[i] = tArray.getResourceId(i, 0);
 }

c,使用已经获取到的资源的id:
  holder.iv.setImageResource(ids[position]); 
d,我们也还可以用这种方式获取string, color, integer, layout, menu等的id.

4,ListView或GridView局部刷新原理的实现:

 private void refreshPartially(int position){
     int firstVisiblePosition = listview.getFirstVisiblePosition();
     int lastVisiblePosition = listview.getLastVisiblePosition();
     if(position>=firstVisiblePosition && position<=lastVisiblePosition){
         View view = listview.getChildAt(position - firstVisiblePosition);
         if(view.getTag() instanceof ViewHolder){
             ViewHolder vh = (ViewHolder)view.getTag();
             //holder.play.setBackgroundResource(resId);//Do something here.
             ...
         }
     }
 }

refreshPartially(int position)

5,Google Volley的单例模式实现:

 package me.pc.mobile.tv.util;

 import android.content.Context;
 import android.graphics.Bitmap;
 import android.util.LruCache;
 import com.android.volley.RequestQueue;
 import com.android.volley.toolbox.ImageLoader;
 import com.android.volley.toolbox.Volley;

 public class VolleySingleton {
     private static VolleySingleton instance;
     private RequestQueue requestQueue;
     private ImageLoader imageLoader;
     private VolleySingleton(Context context) {
         requestQueue = Volley.newRequestQueue(context);
         imageLoader = new ImageLoader(requestQueue, new ImageLoader.ImageCache() {
             private final LruCache<string, bitmap=""> cache = new LruCache<string, bitmap="">(20);

             @Override
             public Bitmap getBitmap(String url) {
                 return cache.get(url);
             }

             @Override
             public void putBitmap(String url, Bitmap bitmap) {
                 cache.put(url, bitmap);
             }
         });
         }

     public static VolleySingleton getInstance(Context context) {
         if (instance == null) {
             instance = new VolleySingleton(context);
         }
         return instance;
     }

     public RequestQueue getRequestQueue() {
         return requestQueue;
     }

     public ImageLoader getImageLoader() {
         return imageLoader;
     }
 }

VolleySingleton.java

采用Volley的单例模式，就避免了在每一个Activity或Frament中都创建一个RequestQueue的麻烦.

6,使用Google Volley来实现文件的分块上传:

 public class PhotoMultipartRequest extends Request {

     private static final String FILE_PART_NAME = "file";

     private MultipartEntityBuilder mBuilder = MultipartEntityBuilder.create();
     private final Response.Listener mListener;
     private final File mImageFile;
     protected Map<string, string=""> headers;

     public PhotoMultipartRequest(String url, ErrorListener errorListener, Listener listener, File imageFile){
         super(Method.POST, url, errorListener);

         mListener = listener;
         mImageFile = imageFile;

         buildMultipartEntity();
     }

     @Override
     public Map<string, string=""> getHeaders() throws AuthFailureError {
         Map<string, string=""> headers = super.getHeaders();

         if (headers == null || headers.equals(Collections.emptyMap())) {
             headers = new HashMap<string, string="">();
         }

         headers.put("Accept", "application/json");

         return headers;
     }

     private void buildMultipartEntity(){
         mBuilder.addBinaryBody(FILE_PART_NAME, mImageFile, ContentType.create("image/jpeg"), mImageFile.getName());
         mBuilder.setMode(HttpMultipartMode.BROWSER_COMPATIBLE);
          mBuilder.setLaxMode().setBoundary("xx").setCharset(Charset.forName("UTF-8"));
     }

     @Override
     public String getBodyContentType(){
         String contentTypeHeader = mBuilder.build().getContentType().getValue();
         return contentTypeHeader;
     }

     @Override
     public byte[] getBody() throws AuthFailureError{
         ByteArrayOutputStream bos = new ByteArrayOutputStream();
         try {
             mBuilder.build().writeTo(bos);
         } catch (IOException e) {
             VolleyLog.e("IOException writing to ByteArrayOutputStream bos, building the multipart request.");
         }

         return bos.toByteArray();
     }

     @Override
     protected Response parseNetworkResponse(NetworkResponse response) {
         T result = null;
         return Response.success(result, HttpHeaderParser.parseCacheHeaders(response));
     }

     @Override
     protected void deliverResponse(T response) {
         mListener.onResponse(response);
     }
 }            

PhotoMultipartRequest.java

代码中使用了Apache的httpclient.jar文件，用于实现文件的拆分与上传.

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