實用代碼段( 一 )

1、精確獲取屏幕尺寸（例如：3.5、4.0、5.0寸屏幕）

  public static double getScreenPhysicalSize(Activity ctx) {
        DisplayMetrics dm = new DisplayMetrics();
        ctx.getWindowManager().getDefaultDisplay().getMetrics(dm);
        double diagonalPixels = Math.sqrt(Math.pow(dm.widthPixels, 2) + Math.pow(dm.heightPixels, 2));
        return diagonalPixels / (160 * dm.density);
    }

2、判斷是否是平板（官方用法）

 public static boolean isTablet(Context context) {
        return (context.getResources().getConfiguration().screenLayout & Configuration.SCREENLAYOUT_SIZE_MASK) >= Configuration.SCREENLAYOUT_SIZE_LARGE;
    }

3、selector的使用，根據狀態修改文字顏色 放在res/color/目錄下

 <selector xmlns:android="http://schemas.android.com/apk/res/android">
   <item android:color="#53c1bd" android:state_selected="true"/>
   <item android:color="#53c1bd" android:state_focused="true"/>
   <item android:color="#53c1bd" android:state_pressed="true"/>
   <item android:color="#777777"/>
</selector>

4、背景色根據狀態更改顏色 android:backgroup

<selector xmlns:android="http://schemas.android.com/apk/res/android">
   <item android:state_selected="true"><shape>            <gradient android:angle="0" android:centerColor="#00a59f" android:endColor="#00a59f" android:startColor="#00a59f" />
   </shape></item>
    <item android:state_focused="true"><shape>
        <gradient android:angle="0" android:centerColor="#00a59f" android:endColor="#00a59f" android:startColor="#00a59f" />
    </shape></item>
   <item android:state_pressed="true"><shape>
        <gradient android:angle="0" android:centerColor="#00a59f" android:endColor="#00a59f" android:startColor="#00a59f" />
    </shape></item>
   <item><shape>
        <gradient android:angle="0" android:centerColor="#00ff00" android:endColor="00ff00" android:startColor="00ff00" />
    </shape></item>
</selector>

5、啓動APK的默認Activity

public static void startApkActivity(final Context ctx, String packageName) {
        PackageManager pm = ctx.getPackageManager();
        PackageInfo pi;
        try {
            pi = pm.getPackageInfo(packageName, 0);
            Intent intent = new Intent(Intent.ACTION_MAIN, null);
            intent.addCategory(Intent.CATEGORY_LAUNCHER);
            intent.setPackage(pi.packageName);

            List apps = pm.queryIntentActivities(intent, 0);

            ResolveInfo ri = apps.iterator().next();
            if (ri != null) {
                String className = ri.activityInfo.name;
                intent.setComponent(new ComponentName(packageName, className));
                ctx.startActivity(intent);
            }
        } catch (NameNotFoundException e) {
            Log.e("startActivity", e);
        }
    }

6、計算寬度 （ 注意如果設置了textStyle，還需要進一步設置TextPaint）

 public static float GetTextWidth(String text, float Size) {
        TextPaint FontPaint = new TextPaint();
        FontPaint.setTextSize(Size);
        return FontPaint.measureText(text);
    }

7、獲取應用程序下所有Activity

public static ArrayList getActivities(Context ctx) {
      ArrayList result = new ArrayList();
      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;
  }

8、檢測字符串中是否包含漢字

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;
    }

9、檢測字符串中只能包含：中文、數字、下劃線(_)、橫線(-)

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

10、檢查有沒有應用程序來接受處理你發出的intent

 public static boolean isIntentAvailable(Context context, String action) {
        final PackageManager packageManager = context.getPackageManager();
        final Intent intent = new Intent(action);
        List list = packageManager.queryIntentActivities(intent, PackageManager.MATCH_DEFAULT_ONLY);
        return list.size() > 0;
    }

11、使用TransitionDrawable實現漸變效果

比使用AlphaAnimation效果要好，可避免出現閃爍問題。

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);
    }

12、掃描指定的文件

用途：從本軟件新增、修改、刪除圖片、文件某一個文件（音頻、視頻）需要更新系統媒體庫時使用，不必掃描整個SD卡。

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

13、Dip轉px

用途：難免在Activity代碼中設置位置、大小等，本方法就很有用了！

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