val displayMetrics = DisplayMetrics()
windowManager.defaultDisplay.getMetrics(displayMetrics)

var width = displayMetrics.widthPixels
var height = displayMetrics.heightPixels

fun Activity.getRealScreenSize(): Pair<Int, Int> { //<width, height>
return if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
    val size = Point()
    display?.getRealSize(size)
    Pair(size.x, size.y)
} else {
    val size = Point()
    windowManager.defaultDisplay.getRealSize(size)
    Pair(size.x, size.y)

}}

这是一个扩展函数，你可以这样在你的活动中使用:

 override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    val pair = getRealScreenSize()
    pair.first //to get width
    pair.second //to get height
}

DisplayMetrics displayMetrics = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
int height = displayMetrics.heightPixels;
int width = displayMetrics.widthPixels;

在某些情况下，这可能行不通。获取getMetrics注释:

Gets display metrics that describe the size and density of this display. The size returned by this method does not necessarily represent the actual raw size (native resolution) of the display. The returned size may be adjusted to exclude certain system decor elements that are always visible. It may be scaled to provide compatibility with older applications that were originally designed for smaller displays. It can be different depending on the WindowManager to which the display belongs. If requested from non-Activity context (e.g. Application context via (WindowManager) getApplicationContext().getSystemService(Context.WINDOW_SERVICE)) metrics will report the size of the entire display based on current rotation and with subtracted system decoration areas. If requested from activity (either using getWindowManager() or (WindowManager) getSystemService(Context.WINDOW_SERVICE)) resulting metrics will correspond to current app window metrics. In this case the size can be smaller than physical size in multi-window mode.

所以，要得到真正的大小:

DisplayMetrics displayMetrics = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getRealMetrics(displayMetrics);
int height = displayMetrics.heightPixels;
int width = displayMetrics.widthPixels;

or:

Point point = new Point();
getWindowManager().getDefaultDisplay().getRealSize(point);
int height = point.y;
int width = point.x;

public class DisplayInfo {
    int screen_height=0, screen_width=0;
    WindowManager wm;
    DisplayMetrics displaymetrics;

    DisplayInfo(Context context) {
        getdisplayheightWidth(context);
    }

    void getdisplayheightWidth(Context context) {
        wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
        displaymetrics = new DisplayMetrics();
        wm.getDefaultDisplay().getMetrics(displaymetrics);
        screen_height = displaymetrics.heightPixels;
        screen_width = displaymetrics.widthPixels;
    }

    public int getScreen_height() {
        return screen_height;
    }

    public int getScreen_width() {
        return screen_width;
    }
}

这里显示的方法已弃用/过时，但仍然可以工作。需要API 13

看看吧

Display disp= getWindowManager().getDefaultDisplay();
Point dimensions = new Point();
disp.getSize(size);
int width = size.x;
int height = size.y;

为什么不

DisplayMetrics displaymetrics = getResources().getDisplayMetrics();

然后使用

displayMetrics.widthPixels

and

displayMetrics.heightPixels