Android实用代码七段

一、获取应用程序下所有Activity

  public static ArrayList<String> getActivities(Context ctx) {
      ArrayList<String> result = new ArrayList<String>();
      Intent intent = new Intent(Intent.ACTION_MAIN,null);
      intent.setPackage(ctx.getPackageName());
      for (ResolveInfo info : ctx.getPackageManager().queryIntentActivities(intent, 0)) {
          result.add(info.activityInfo.name);
      }
      return result;
  }

二、检测字符串中是否包含汉字

    public static boolean checkChinese(String sequence) {
        final String format = "[//u4E00-//u9FA5//uF900-//uFA2D]";
        boolean result = false;
        Pattern pattern = Pattern.compile(format);
        Matcher matcher = pattern.matcher(sequence);
        result = matcher.find();
        return result;
    }

三、检测字符串中只能包含：中文、数字、下划线(_)、横线(-)

    public staticboolean checkNickname(String sequence) {
        final String format = "[^//u4E00-//u9FA5//uF900-//uFA2D//w-_]";
        Pattern pattern = Pattern.compile(format);
        Matcher matcher = pattern.matcher(sequence);
        return !matcher.find();
    }

四、检查有没有应用程序来接受处理你发出的intent

  public static boolean isIntentAvailable(Context context,String action){       

       final PackageManager packageManager = context.getPackageManager();        

       final Intent intent = new Intent(action);        

       List<ResolveInfo> list = packageManager.queryIntentActivities(intent, PackageManager.MATCH_DEFAULT_ONLY);        

       return list.size() > 0;    

  }

五、使用TransitionDrawable实现渐变效果

    private void setImageBitmap(ImageView imageView, Bitmap bitmap) {
        // Use TransitionDrawable to fade in.
        final TransitionDrawable td = new TransitionDrawable(new Drawable[] { new ColorDrawable(android.R.color.transparent), new BitmapDrawable(mContext.getResources(), bitmap) });
        //noinspection deprecation
        imageView.setBackgroundDrawable(imageView.getDrawable());
        imageView.setImageDrawable(td);
        td.startTransition(200);
    }

比使用AlphaAnimation效果要好，可避免出现闪烁问题。

六、 扫描指定的文件

sendBroadcast(new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE, uri));

用途：从本软件新增、修改、删除图片、文件某一个文件（音频、视频）需要更新系统媒体库时使用，不必扫描整个SD卡。

七、Dip转px

    public staticint dipToPX(final Context ctx,float dip) {
        return (int)TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dip, ctx.getResources().getDisplayMetrics());
    }