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;
}

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();
    }
}

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"));
}

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();
        }
    }
}

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;
}

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>

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.
            ...
        }
    }
}

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;
    }
}

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);
    }
}            

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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