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：
 1 View rootView = getWindow().getDecorView().findViewById(android.R.id.content); 
或者：
 1 View rootView = findViewById(android.R.id.content); 
或者：
 1 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:

1 public static Bitmap getScreenShot(View view) {
2     View screenView = view.getRootView();
3     screenView.setDrawingCacheEnabled(true);
4     Bitmap bitmap = Bitmap.createBitmap(screenView.getDrawingCache());
5     screenView.setDrawingCacheEnabled(false);
6     return bitmap;
7 }

getScreenShot

c,将当前屏幕的截屏保存至SDCard:

 1 private final static String dir = Environment.getExternalStorageDirectory().getAbsolutePath() + "/Screenshots";
 2 public static void store(Bitmap bm, String fileName){
 3     File dir = new File(dir);
 4     if(!dir.exists())
 5         dir.mkdirs();
 6     File file = new File(dir, fileName);
 7     try {
 8         FileOutputStream fOut = new FileOutputStream(file);
 9         bm.compress(Bitmap.CompressFormat.PNG, 85, fOut);
10         fOut.flush();
11         fOut.close();
12     } catch (Exception e) {
13         e.printStackTrace();
14     }
15 }

store(Bitmap bm, String fileName)

d,最后将该图片文件分享出来:

 1 private void shareImage(String file){
 2     Uri uri = Uri.fromFile(file);
 3     Intent intent = new Intent();
 4     intent.setAction(Intent.ACTION_SEND);
 5     intent.setType("image/*");
 6     intent.putExtra(android.content.Intent.EXTRA_SUBJECT, "");
 7     intent.putExtra(android.content.Intent.EXTRA_TEXT, "");
 8     intent.putExtra(Intent.EXTRA_STREAM, uri);
 9     startActivity(Intent.createChooser(intent, "Share Screenshot"));
10 }

shareImage(String file)

2,如何对HTML5中的视频截图:

a,初始化WebView:

1 String webUrl = ...;
2 VideoView vv;
3 mWebView = (WebView) findViewById(R.id.webview);
4 mWebView.setWebChromeClient(chromeClient);
5 mWebView.setWebViewClient(wvClient);
6 mWebView.getSettings().setJavaScriptEnabled(true);
7 mWebView.getSettings().setPluginsEnabled(true);
8 mWebView.loadUrl(webUrl);

b,覆盖WebChromeClient中的onShowCustomView方法:

 1 @Override
 2 public void onShowCustomView(View view, CustomViewCallback callback) {
 3     super.onShowCustomView(view, callback);
 4     if (view instanceof FrameLayout){
 5         FrameLayout frame = (FrameLayout) view;
 6         if (frame.getFocusedChild() instanceof VideoView){
 7             vv = (VideoView) frame.getFocusedChild();
 8         }
 9     }
10 }

onShowCustomView(View view, CustomViewCallback callback)

c,截取VideoView中播放的视频内容:

1 private Bitmap capture(VideoView vv){
2     MediaMetadataRetriever rev = new MediaMetadataRetriever();
3     rev.setDataSource(this, uri);//this is a Context;
4     Bitmap bitmap = rev.getFrameAtTime(vv.getCurrentPosition() * 1000, MediaMetadataRetriever.OPTION_CLOSEST_SYNC);
5     return bitmap;
6 }

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:

1 <integer-array name="frag_home_ids">
2     <item>@drawable/frag_home_credit_return_money</item>
3     <item>@drawable/frag_home_transfer</item>
4     <item>@drawable/frag_home_balance</item>
5     <item>@drawable/frag_home_charge</item>
6     <item>@drawable/frag_home_finance_cdd</item>
7     <item>@drawable/frag_home_finance_ybjr</item>
8     <item>@drawable/frag_home_more</item>
9 </integer-array>

arrays.xml

b,通过编码的方式获取integer-array中的资源id整型值:

1 TypedArray tArray = getResources().obtainTypedArray(R.array.frag_home_ids);
2 int count = tArray.length();
3 int[] ids = new int[count];
4 for (int i = 0; i < ids.length; i++) {
5     ids[i] = tArray.getResourceId(i, 0);
6 }

c,使用已经获取到的资源的id:
 1 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:

 1 private void refreshPartially(int position){
 2     int firstVisiblePosition = listview.getFirstVisiblePosition();
 3     int lastVisiblePosition = listview.getLastVisiblePosition();
 4     if(position>=firstVisiblePosition && position<=lastVisiblePosition){
 5         View view = listview.getChildAt(position - firstVisiblePosition);
 6         if(view.getTag() instanceof ViewHolder){
 7             ViewHolder vh = (ViewHolder)view.getTag();
 8             //holder.play.setBackgroundResource(resId);//Do something here.
 9             ...
10         }
11     }
12 }

refreshPartially(int position)

5,Google Volley的单例模式实现:

 1 package me.pc.mobile.tv.util;
 2
 3 import android.content.Context;
 4 import android.graphics.Bitmap;
 5 import android.util.LruCache;
 6 import com.android.volley.RequestQueue;
 7 import com.android.volley.toolbox.ImageLoader;
 8 import com.android.volley.toolbox.Volley;
 9
10 public class VolleySingleton {
11     private static VolleySingleton instance;
12     private RequestQueue requestQueue;
13     private ImageLoader imageLoader;
14     private VolleySingleton(Context context) {
15         requestQueue = Volley.newRequestQueue(context);
16         imageLoader = new ImageLoader(requestQueue, new ImageLoader.ImageCache() {
17             private final LruCache<string, bitmap=""> cache = new LruCache<string, bitmap="">(20);
18
19             @Override
20             public Bitmap getBitmap(String url) {
21                 return cache.get(url);
22             }
23
24             @Override
25             public void putBitmap(String url, Bitmap bitmap) {
26                 cache.put(url, bitmap);
27             }
28         });
29         }
30
31     public static VolleySingleton getInstance(Context context) {
32         if (instance == null) {
33             instance = new VolleySingleton(context);
34         }
35         return instance;
36     }
37
38     public RequestQueue getRequestQueue() {
39         return requestQueue;
40     }
41
42     public ImageLoader getImageLoader() {
43         return imageLoader;
44     }
45 }

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:

 1 public class PhotoMultipartRequest extends Request {
 2
 3     private static final String FILE_PART_NAME = "file";
 4
 5     private MultipartEntityBuilder mBuilder = MultipartEntityBuilder.create();
 6     private final Response.Listener mListener;
 7     private final File mImageFile;
 8     protected Map<string, string=""> headers;
 9
10     public PhotoMultipartRequest(String url, ErrorListener errorListener, Listener listener, File imageFile){
11         super(Method.POST, url, errorListener);
12
13         mListener = listener;
14         mImageFile = imageFile;
15
16         buildMultipartEntity();
17     }
18
19     @Override
20     public Map<string, string=""> getHeaders() throws AuthFailureError {
21         Map<string, string=""> headers = super.getHeaders();
22
23         if (headers == null || headers.equals(Collections.emptyMap())) {
24             headers = new HashMap<string, string="">();
25         }
26
27         headers.put("Accept", "application/json");
28
29         return headers;
30     }
31
32     private void buildMultipartEntity(){
33         mBuilder.addBinaryBody(FILE_PART_NAME, mImageFile, ContentType.create("image/jpeg"), mImageFile.getName());
34         mBuilder.setMode(HttpMultipartMode.BROWSER_COMPATIBLE);
35          mBuilder.setLaxMode().setBoundary("xx").setCharset(Charset.forName("UTF-8"));
36     }
37
38     @Override
39     public String getBodyContentType(){
40         String contentTypeHeader = mBuilder.build().getContentType().getValue();
41         return contentTypeHeader;
42     }
43
44     @Override
45     public byte[] getBody() throws AuthFailureError{
46         ByteArrayOutputStream bos = new ByteArrayOutputStream();
47         try {
48             mBuilder.build().writeTo(bos);
49         } catch (IOException e) {
50             VolleyLog.e("IOException writing to ByteArrayOutputStream bos, building the multipart request.");
51         }
52
53         return bos.toByteArray();
54     }
55
56     @Override
57     protected Response parseNetworkResponse(NetworkResponse response) {
58         T result = null;
59         return Response.success(result, HttpHeaderParser.parseCacheHeaders(response));
60     }
61
62     @Override
63     protected void deliverResponse(T response) {
64         mListener.onResponse(response);
65     }
66 }            

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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