Some useful methods in Android development that you don't know

setBackgroundResource(0) can remove the background color of View

Resources.getSystem().getDisplayMetrics().density You can get the screen density without using Context

By overloading ViewGroup dispatchDraw can implement a simple mask effect. For example, when pulling down to refresh, you can add a layer of mask to the contentView. canvas.drawRect(0, mContentView.getTranslationY(), getWidth(), getHeight(), mMaskPaint);

new View can use View.generateViewId() (available for API 17 or above) to generate id, the system Guaranteed to be unique

When using GridView, the effect is better when using android:padding and android:clipToPadding="false" together.

In the layout file, if it is just for placeholder, you can use Space to replace View. The best thing is that Space can skip the Draw process.

TypedValue.applyDimension(int unit, float value, DisplayMetrics metrics) facilitates conversion between dp, px, sp.

Activity.startActivities() The most direct understanding of this method is to use intent to open multiple activities

TextUtils.isEmpty() If the incoming String is NULL or Length is 0, it will return true .

Html.fromHtml() If you are familiar with Html, you can quickly handle some rich text operations through this method. For example, processing of hyperlinks and graphic and text layout.

TextView.setError() Set text box error reminder

Build.VERSION_CODES Sometimes our app needs to perform different operations according to different SDK versions

PhoneNumberUtils.convertKeypadLettersToDigits This method is simple and crude. It will convert the entered letters into numbers according to the mapping on the keyboard.

ArgbEvaluator ArgbEvaluator.evaluate(float fraction, Object startValue, Object endValue); Generate a new color based on a starting color value, an ending color value and an offset, achieving something similar to the bottom of WeChat in minutes Bar sliding color gradient.

ValueAnimator.reverse() Smoothly cancel the animation effect

DateUtils.formatDateTime()) This method can output the corresponding formatted time or date

Pair This class can be used To store a "set" of data. But it is not the relationship between key and value.

SparseArray Currently, there are many places that use SparseArray to replace hashMap from the perspective of performance optimization to save memory and improve performance.

Linkify.addLinks() This class makes it easier to add hyperlinks to text.

android.media.ThumbnailUtils This class is mainly used to handle thumbnail-related work, such as: used to obtain thumbnails of media (pictures, videos);

Bitmap.extractAlpha () ;Return a new Bitmap, capturing the alpha value of the original image. Sometimes we need to dynamically modify the background image of an element and do not want to use multiple images. Through this method, combined with Canvas and Paint, we can dynamically modify the color of a solid-color Bitmap.

When there are messages that need to be transmitted between modules, use LocalBroadcastManager instead of Listener to decouple the modules. In addition to decoupling, sending messages and executing messages are separated by one thread cycle, which can reduce the method call chain. I encountered a StackOverflow problem when the method call chain was too long.

Static variables should not directly or indirectly reference Activity, Service, etc. This will make the Activity and all the objects it refers to unable to be released. Then, as the user operates for a long time, the memory will skyrocket.

One feature of the Handler mechanism is that it will not end with the end of the life cycle of Activity and Service. In other words, if you post a Delay Runnable and then exit the Activity before the Runnable is executed, the Runnable will still be executed after the time is up. If the Runnable contains an operation to update the View, the program crashes.

Many people like to use Context.runOnUiThread when updating Views in child threads. This method has a disadvantage, that is, once the Context life cycle ends, such as when the Activity has been destroyed, it will crash as soon as it is called.

SharedPreferences.Editor.commit This method is synchronous and will not return until the data is synchronized to Flash. The IO operation is uncontrollable, so try to use the apply method instead. apply is only supported in API Level>=9 and needs to be compatible. However, the latest support v4 package has already taken care of it for us, just use SharedPreferencesCompat.EditorCompat.getInstance().apply(editor).

PackageManager.getInstalledPackages This method is often used. You may not know that when the number of results obtained is relatively large, it may take seconds to call it on some models, so try to use it in a child thread. used in. In addition, if there are too many results and exceed the upper limit of the maximum Binder data transmission set by the system, a TransactionException will occur. If you use this method to obtain the list of installed applications on the machine, it is best to take precautions.

If you use Context.startActivity to start an external application, it is best to do some exception prevention, because if the corresponding application cannot be found, an exception will be thrown. If you want to open an Activity within the application, you may want to use an explicit Intent, which can improve the efficiency of the system's search for the target Activity.

The life cycle of Application is the life cycle of the process. The Application will be destroyed only when the process is killed. Even if no Activity or Service is running, the Application will exist. Therefore, in order to reduce memory pressure, try not to reference large objects, Context, etc. in Application.

getWindow().setLayout(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT); The full-screen method must be set after setContentView.

The setCurrentItem of viewpager must be called after the setAdapter method. It will have an effect.

Determine whether the phone is in airplane mode boolean isEnabled = Settings.System.getInt(context.getContentResolver(), Settings.System.AIRPLANE_MODE_ON, 0) == 1;

Traverse The best method of HashMap

public static void printMap(Map mp) {   
 for (Map.Entry m : mp.entrySet()) {  

       System.out.println(m.getKey() + ":" + m.getValue());   }
}

Use Java to generate random integer numbers in a range

public static int randInt(int min, int max) { 
   Random rand = new Random();   
   int randomNum = rand.nextInt((max - min) + 1) + min;    
   return randomNum;
}

If the subclass implements the Serializable interface but the parent class does not, the parent class will not be serialized. But at this time, the parent class must have a parameterless constructor, otherwise an InvalidClassException will be thrown.

Transient keyword modified variables can limit serialization.

When using JakeWharton's TabPageIndicator, if you need to do some time-consuming operations first and then display the TabPageIndicator, you need to set mIndirector.setVisibility(View.GONE) first; and then mIndirector after the time-consuming task is completed. setVisibility(View.VISIBLE); Otherwise, an error will be reported

Calling sequence between class inheritance Parent class static members -> Subclass static members -> Parent class ordinary member initialization and initialization block -> Parent class Construction method -> Subclass ordinary member initialization and initialization block -> Subclass construction method

Huawei mobile phone cannot display log solution,.Dial interface input (*#*#2846579#*#*) Service menu will appear.Go to "ProjectMenu" -> "Background Setting" -> "Log Setting"Open "Log switch" and set it to ON.Open "Log level setting" and set the log level you wish.

Background services often appear due to restarts and the like. The parameter passed by Intent in onStartCommand() is null. Change the return value in onStartCommand() to return super.onStartCommand(intent, Service.START_REDELIVER_INTENT, startId); can solve the problem. The following introduces the meaning of several flags

PopupWindow and Dialog cannot be displayed when the Activity is not fully displayed

Do not use SharedPreferences to share data between multiple processes. Although it is possible (MODE_MULTI_PROCESS), it is extremely unstable

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