【Android】理解RemoteViews

ref:
《Android 开发艺术探索》 05-理解RemoteViews 抄书系列

這篇文章是對解釋remoteview超詳細，比官網還有用，先記錄一下。

如果早先看到這，懂裡面的原理，可以少走冤枉路。

【Android】Teaching Android on Youtube

Android Developers

Google Developers for Chinese language

【Java】Regular Expression Pattern

判斷正負實數 

• [+-]?((\d+\.?\d*)|(\.\d+))
• https://regex101.com/r/zB7vV3/27

String pattern = "[+-]?((\\d+\\.?\\d*)|(\\.\\d+))";
// Create a Pattern objectPattern r = Pattern.compile(pattern);// Now create matcher object.Matcher m = r.matcher(expression);int x = 0;while (m.find()) {
    Log.d("[FIND]", x + ":-->" + m.group(x++));}

return m.find();

判斷整數加減乘除

• ^(\d+[\+\-\*\/]{1})+\d+$
• https://regex101.com/r/zB7vV3/28

規則

• http://ccckmit.wikidot.com/regularexpression

移除開頭多餘0

expression.replaceAll("^(0+)", "");

或

expression.replaceFirst("^0+", "")

【Finance】2018信用卡規劃

ref:
2018信用卡用卡規劃

【Android Studio】Instant Run is disabled for non-debug variants

If you have manually set it in the manifest, then remove it and let the IDE automatically assign it. 
If you are using Gradle, make sure that your current variant is debuggable.

buildTypes {
    release {
        debuggable true  //發佈時 記得改為false
    }

【Android】Experimenting with Gradle dependencies

ref:
http://alexfu.github.io/android/2017/11/07/experimenting-with-gradle-dependencies.html

https://www.ithome.com.tw/news/118397

除了用戶方面升級外，研究人員也建議，app開發商可以在WindowsManager中啟動FLAG_SECURE參數， 可確保app視窗內容不得被螢幕擷圖，或是在不安全環境下顯示。

【Android】This AsyncTask class should be static or leaks might occur

How to use a static inner AsyncTask class

ref:https://stackoverflow.com/a/46166223

To prevent leaks, you can make the the inner class static. The problem with that, though, is that you no longer have access to the Activity's UI views or member variables. You can pass in a reference to the Context but then you run the same risk of a memory leak. (Android can't garbage collect the Activity after it closes if the AsyncTask class has a strong reference to it.) The solution is to make a weak reference to the Activity (or whatever Context you need).

public class MyActivity extends AppCompatActivity {

    int mSomeMemberVariable = 123;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // start the AsyncTask, passing the Activity context
        // in to a custom constructor 
        new MyTask(this).execute();
    }

    private static class MyTask extends AsyncTask<Void, Void, String> {

        private WeakReference<MyActivity> activityReference;

        // only retain a weak reference to the activity 
        MyTask(MyActivity context) {
            activityReference = new WeakReference<>(context);
        }

        @Override
        protected String doInBackground(Void... params) {

            // do some long running task...

            return "task finished";
        }

        @Override
        protected void onPostExecute(String result) {

            // get a reference to the activity if it is still there
            MyActivity activity = activityReference.get();
            if (activity == null) return;

            // modify the activity's UI
            TextView textView = activity.findViewById(R.id.textview);
            textView.setText(result);

            // access Activity member variables
            activity.mSomeMemberVariable = 321;
        }
    }
}

Notes

• As far as I know, this type of memory leak danger has always been true, but I only started seeing the warning in Android Studio 3.0. A lot of the main AsyncTask tutorials out there still don't deal with it (see here, here, here, and here).
• You would also follow a similar procedure if your AsyncTask were a top-level class. A static inner class is basically the same as a top-level class in Java.
• If you don't need the Activity itself but still want the Context (for example, to display a Toast), you can pass in a reference to the app context. In this case the AsyncTask constructor would look like this:

  private WeakReference<Application> appReference;
  
  MyTask(Application context) {
      appReference = new WeakReference<>(context);
  }

• There are some arguments out there for ignoring this warning and just using the non-static class. After all, the AsyncTask is intended to be very short lived (a couple seconds at the longest), and it will release its reference to the Activity when it finishes anyway. See this and this.
• Excellent article: How to Leak a Context: Handlers & Inner Classes

【Java】 BarCode

ref:

• 無聊技術研究: 由 Code 128 Font 建立 BarCode (含規則)
• Barcode4J examples
• woo-j/OkapiBarcode
• zxing

【Android】如何顯示Splash Screen Image不會Delay

翻譯自 Boy Wang@medium

ref: Android Drawable

很多android app都會使用splash screen，如下：

<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".SplashScreenActivity">

    <android.support.v7.widget.AppCompatImageView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_margin="40dp"
        android:scaleType="centerInside"
        android:layout_gravity="center"
        app:srcCompat="@drawable/img_splash_screen"/>
</FrameLayout>

通常在splash screen會顯示只有一個image的layout，這樣沒問題嗎？

是的，除了在顯示splash screen前會短暫地顯示一個全白畫面。"短暫地"是多長的時間取決於你的android硬體設備。WHY？



根據以下影片Cyril Mottier關於view hierarchy的演講，得知window theme的畫面顯示優先權高於你的layout。

那要如何讓白畫面消失？幸運地，android 提供了Drawable和android:windowBackground屬性。

解決辦法：

1.Turn the splash screen to a Drawable.

drawable/img_splash_screen_for_window_theme.xml

2.Add android:windowBackground in your values/styles.xml.

values/styles.xml

3.Add android:windowBackground in your values/styles.xml.