Android Cheatsheet

Android Studio

opt + return to import missing classes.
cmd + o to navigate to Class.
sht + cmd + o to navigate to File.
opt + cmd + o to navigate to Symbol.
cmd + l to navigate to Line.
cmd + fn + F9 to build program.
ctr + r to run application.
ctr + opt + r to run program.
cmd + n to add a new method.
cmd + b to find declaration/implemetation and go to.
cmd + e to open recent edited files.
opt + fn + F7 to find usage.
cmd + opt + <- to back to the last position where the cursor pointed.
cmd + d to copy and paste a line.
cmd + sft + f to find in path.
select the lines you want to move, sht + opt + up/down to move lines.
fn + sht + F6 to modify variable names

ADB logcat

ADB command to see the debug log with MyTag.

adb logcat -v time | grep D/MyTag

Gradle: Add shared project

In app’s build.gradle, add:

dependencies {
    compile project(':zxing-android-embedded')
}

Reference

24.7. Project lib dependencies

Get device information

// get device information
String s = "Debug-infos";
s += "\nOS Version: " + System.getProperty("os.version") + "(" + Build.VERSION.INCREMENTAL + ")";
s += "\nOS API Level: " + Build.VERSION.SDK_INT;
s += "\nDevice: " + Build.DEVICE;
s += "\nBrand: " + Build.BRAND;
s += "\nManufacturer: " + Build.MANUFACTURER;
s += "\nModel (and Product): " + Build.MODEL + "(" + Build.PRODUCT + ")";
Log.v("Device Info:", s);

Result would be like this:

V/Device Info: Debug-infos
               OS Version: 3.10.0-genymotion-g08e528d(eng.buildbot.20160110.195928)
               OS API Level: 23
               Device: vbox86p
               Brand: Android
               Manufacturer: Genymotion
               Model (and Product): Google Nexus 6P - 6.0.0 - API 23 - 1440x2560(vbox86p)

Reference

Get UTC timestamp

Long tsLong = System.currentTimeMillis()/1000;
String ts = tsLong.toString();

I do not use TimingLogger as it is more suitable for calculating code execution time. We are not measuring code execution time here. Besides, developers have to set a system property like:

$ adb shell
# setprop
usage: setprop <key> <value>
# setprop log.tag.MyTag VERBOSE
#

to make Log.isLoggable become true. Otherwise the addSplit and dumpToLog call will do nothing.

Use getTime() of Date object,

Date date = new Date();
long timestamp = date.getTime();

you will also get time in millisecond like System.currentTimeMillis() in 12 digits. To get 10 digits of timestamp, try date.getTime()/1000.

Reference

Get the current language in device

Locale.getDefault().getDisplayLanguage();

Someone has checked the Locale methods on an Android 4.1.2 device, and the results:

Locale.getDefault().getLanguage()       ---> en
Locale.getDefault().getISO3Language()   ---> eng
Locale.getDefault().getCountry()        ---> US
Locale.getDefault().getISO3Country()    ---> USA
Locale.getDefault().getDisplayCountry() ---> United States
Locale.getDefault().getDisplayName()    ---> English (United States)
Locale.getDefault().toString()          ---> en_US
Locale.getDefault().getDisplayLanguage()---> English

Reference

Get the current language in device

Make a clickable URL in Textview and return true if the URL was clicked

Add a TextView in layout.xml

<TextView
    android:id="@+id/my_link"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:autoLink="web"
    android:onClick="clickURL"/>

android:autoLink="web" will find an URL and create a link even if android:linksClickable is not set, links are by default clickable. You don’t have to keep the URL alone, even in the middle of a text it will be detected and clickable.

To set a link via the code, same principle, no need for pattern or android:autoLink in layout, the link is found automatically using Linkify:

TextView text_view = (TextView) findViewById(id.my_link);
text_view.setText("Click my web site: www.stackoverflow.com");
Linkify.addLinks(text_view, Linkify.WEB_URLS);

public void clickURL(View view) {

    //do something you like while the Textview is clicked
    ifClick = true;
}

Reference

Get device screen dpi

DisplayMetrics metrics = getResources().getDisplayMetrics();
int densityDpi = (int)(metrics.density * 160f);

metrics.densityDpi property will be one of the constants (120, 160, 213, 240, 320, 480 or 640 dpi).

Reference

getting the screen density programmatically in android?

Change locale at runtime

private Locale myLocale;
public void set_locale(String lang) {
      myLocale = new Locale(lang);
      Resources res = getResources();
      Configuration conf = res.getConfiguration();
      conf.locale = myLocale;
      res.updateConfiguration(conf, res.getDisplayMetrics());

      recreate();
//      Intent intent = new Intent(this, DisplayMessageActivity.class);
//      startActivity(intent);

For Traiditional Chinese or Simplified Chinese, you should rather write:

new Locale("zh", "TW")

Reference

Content behind CoordinatorLayout AppBarLayout

If you created a NavigationDrawer with Android Studio’s default template, you will find once you add contents in content_xxx.xml file, the contect end up being behind the AppBar(ToolBar).

To solve this, add layout_behavior to your ViewGroup(RelativeLayout, ScrollView, FrameLayout, etc.) like:

xmlns:app="http://schemas.android.com/apk/res-auto"
app:layout_behavior="@string/appbar_scrolling_view_behavior"

Reference

Content behind CoordinatorLayout AppBarLayout

Alert Dialog

An example of making a dialog:

public void showAlertDialog() {
    AlertDialog.Builder builder = new AlertDialog.Builder(this);
    builder.setMessage(R.string.dialog_message).setTitle(R.string.dialog_tile);
    builder.setPositiveButton("OK", null);
    AlertDialog dialog = builder.create();
    dialog.show();
}

Result:

Imgur

Reference

Dialog Fragment

Dialog fragment is a fragment which can show fragment in dialog box.

To implement a dialog fragment:

#1. Create a new class like:

public static class MyAlertDialogFragment extends DialogFragment {

    public static MyAlertDialogFragment newInstance(int title) {
        MyAlertDialogFragment frag = new MyAlertDialogFragment();
        Bundle args = new Bundle();
        args.putInt("title", title);
        frag.setArguments(args);
        return frag;
    }

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        int title = getArguments().getInt("title");

        return new AlertDialog.Builder(getActivity())
                .setIcon(R.drawable.alert_dialog_icon)
                .setTitle(title)
                .setPositiveButton(R.string.alert_dialog_ok,
                    new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int whichButton) {
                            ((FragmentAlertDialog)getActivity()).doPositiveClick();
                        }
                    }
                )
                .setNegativeButton(R.string.alert_dialog_cancel,
                    new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int whichButton) {
                            ((FragmentAlertDialog)getActivity()).doNegativeClick();
                        }
                    }
                )
                .create();
    }
}

#2. The activity creating this fragment may have the following methods to show the dialog and receive results from it:

void showDialog() {
    DialogFragment newFragment = MyAlertDialogFragment.newInstance(
            R.string.alert_dialog_two_buttons_title);
    newFragment.show(getFragmentManager(), "dialog");
}

public void doPositiveClick() {
    // Do stuff here.
    Log.i("FragmentAlertDialog", "Positive click!");
}

public void doNegativeClick() {
    // Do stuff here.
    Log.i("FragmentAlertDialog", "Negative click!");
}

More flexible way to implement:

Reference

DialogFragment

Get Carrier Name

TelephonyManager manager = (TelephonyManager)context.getSystemService(Context.TELEPHONY_SERVICE);
String carrierName = manager.getNetworkOperatorName();

Reference

How to find out carrier’s name in Android