Android实用代码（1）

1.精确获取屏幕尺寸（例如：3.5、4.0、5.0）

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);

}</code></pre>
2.判断是否是平板（官方用法）
 public static boolean isTablet(Context context) {
        return (context.getResources().getConfiguration().screenLayout & Configuration.SCREENLAYOUT_SIZE_MASK) >= Configuration.SCREENLAYOUT_SIZE_LARGE;
}
3.启动APK的默认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<ResolveInfo> 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);
    }
}

4.检测字符串中是否包含汉字
public static boolean checkChinese(String sequence) {
        final String format = "[u4E00-u9FA5uF900-uFA2D]";
        boolean result = false;
        Pattern pattern = Pattern.compile(format);
        Matcher matcher = pattern.matcher(sequence);
        result = matcher.find();
        return result;
}
5.检测字符串中只能包含：中文、数字、下划线(_)、横线(-)
public static boolean checkNickname(String sequence) {
        final String format = "[^u4E00-u9FA5uF900-uFA2Dw-_]";
        Pattern pattern = Pattern.compile(format);
        Matcher matcher = pattern.matcher(sequence);
        return !matcher.find();
    } 
6.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);
    }
7.Dip转px
public static int dipToPX(final Context ctx,float dip) {
        return (int)TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,dip,ctx.getResources().getDisplayMetrics());
}
用途：难免在Activity代码中设置位置、大小等，本方法就很有用了！
                        
（编辑：李大同）
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