Android screen resolution retrieval method-source code analysis

This article from http://blog.csdn.net/liuxian13183/, reference must indicate the source!

In the adaptation process, sometimes we use the screen width and height. How can we obtain the screen resolution?

There are two methods:

The first method is to obtain the Diaplay object through the WindowManager interface and obtain the Diaplay object through the Display object.

WindowManager manager = (WindowManager) context

. GetSystemService (Context. WINDOW_SERVICE );
Display display = manager. getDefaultDisplay ();

DisplayMetrics outMetrics = new DisplayMetrics ();
Display. getMetrics (outMetrics );

ScreenHeight = outMetrics. heightPixels;

ScreenWidth = outMetrics. widthPixels;
// ScreenHeight = display. getHeight (); this method has been deprecated
// ScreenWidth = display. getWidth (); this method has been deprecated

Or

From the source code, take height as an example:

Private final Point mTmpPoint = new Point ();

    public int getHeight() {        synchronized (mTmpPoint) {            long now = SystemClock.uptimeMillis();            if (now > (mLastGetTime+20)) {                getSizeInternal(mTmpPoint, true);                mLastGetTime = now;            }            return mTmpPoint.y;        }    }

It is mainly used to find the y coordinate of mTmpPoint.

    private void getSizeInternal(Point outSize, boolean doCompat) {        try {            IWindowManager wm = getWindowManager();            if (wm != null) {                wm.getDisplaySize(outSize);                CompatibilityInfo ci;                if (doCompat && (ci=mCompatibilityInfo.getIfNeeded()) != null) {                    synchronized (mTmpMetrics) {                        mTmpMetrics.noncompatWidthPixels = outSize.x;                        mTmpMetrics.noncompatHeightPixels = outSize.y;                        mTmpMetrics.density = mDensity;                        ci.applyToDisplayMetrics(mTmpMetrics);                        outSize.x = mTmpMetrics.widthPixels;                        outSize.y = mTmpMetrics.heightPixels;                    }                }            } else {                // This is just for boot-strapping, initializing the                // system process before the window manager is up.                outSize.x = getRawWidth();                outSize.y = getRawHeight();            }            if (false) {                RuntimeException here = new RuntimeException("here");                here.fillInStackTrace();                Slog.v(TAG, "Returning display size: " + outSize, here);            }            if (DEBUG_DISPLAY_SIZE && doCompat) Slog.v(                    TAG, "Returning display size: " + outSize);        } catch (RemoteException e) {            Slog.w("Display", "Unable to get display size", e);        }    }

Then we found that setting metrics through the CompatibilityInfo object is one method, and the other is getRawHeight ()

    public int getRawHeight() {        int h = getRawHeightNative();        if (DEBUG_DISPLAY_SIZE) Slog.v(                TAG, "Returning raw display height: " + h);        return h;    }    private native int getRawHeightNative();

The native method is implemented at the underlying layer.

Method 2: Use the Resource object to obtain DisplayMetrics.

DisplayMetrics metrics = context. getResources (). getDisplayMetrics ();

ScreenHeight = metrics. heightPixels;
ScreenWidth = metrics. widthPixels;

In general, DisplayMetrics needs to be obtained. Let's take a look at its composition:

    /**     * Standard quantized DPI for low-density screens.     */    public static final int DENSITY_LOW = 120;    /**     * Standard quantized DPI for medium-density screens.     */    public static final int DENSITY_MEDIUM = 160;    /**     * Standard quantized DPI for 720p TV screens.  Applications should     * generally not worry about this density, instead targeting     * {@link #DENSITY_XHIGH} for 1080p TV screens.  For situations where     * output is needed for a 720p screen, the UI elements can be scaled     * automatically by the platform.     */    public static final int DENSITY_TV = 213;    /**     * Standard quantized DPI for high-density screens.     */    public static final int DENSITY_HIGH = 240;    /**     * Standard quantized DPI for extra-high-density screens.     */    public static final int DENSITY_XHIGH = 320;

Default Density values

Default implementation method:

    public void setToDefaults() {        widthPixels = 0;        heightPixels = 0;        density = DENSITY_DEVICE / (float) DENSITY_DEFAULT;        densityDpi = DENSITY_DEVICE;        scaledDensity = density;        xdpi = DENSITY_DEVICE;        ydpi = DENSITY_DEVICE;        noncompatWidthPixels = 0;        noncompatHeightPixels = 0;    }

Generally, the following aspects must be implemented to obtain the desired value.

    public void setTo(DisplayMetrics o) {        widthPixels = o.widthPixels;        heightPixels = o.heightPixels;        density = o.density;        densityDpi = o.densityDpi;        scaledDensity = o.scaledDensity;        xdpi = o.xdpi;        ydpi = o.ydpi;        noncompatWidthPixels = o.noncompatWidthPixels;        noncompatHeightPixels = o.noncompatHeightPixels;        noncompatDensity = o.noncompatDensity;        noncompatScaledDensity = o.noncompatScaledDensity;        noncompatXdpi = o.noncompatXdpi;        noncompatYdpi = o.noncompatYdpi;    }

Check the Resource class

    public Resources(AssetManager assets, DisplayMetrics metrics,            Configuration config, CompatibilityInfo compInfo) {        mAssets = assets;        mMetrics.setToDefaults();        mCompatibilityInfo = compInfo;        updateConfiguration(config, metrics);        assets.ensureStringBlocks();    }

See updateConfiguration (config, metrics); Method

    /**     * Store the newly updated configuration.     */    public void updateConfiguration(Configuration config,            DisplayMetrics metrics) {        updateConfiguration(config, metrics, null);    }

    /**     * @hide     */    public void updateConfiguration(Configuration config,            DisplayMetrics metrics, CompatibilityInfo compat) {        synchronized (mTmpValue) {            if (false) {                Slog.i(TAG, "**** Updating config of " + this + ": old config is "                        + mConfiguration + " old compat is " + mCompatibilityInfo);                Slog.i(TAG, "**** Updating config of " + this + ": new config is "                        + config + " new compat is " + compat);            }            if (compat != null) {                mCompatibilityInfo = compat;            }            if (metrics != null) {                mMetrics.setTo(metrics);            }

We will see this result, so when the Resources is formed, metrics has been written.
However, we just used this. getResouces to directly obtain the Resource object.

ContextThemeWrapper:

    @Override    public Resources getResources() {        if (mResources != null) {            return mResources;        }        if (mOverrideConfiguration == null) {            mResources = super.getResources();            return mResources;        } else {            Context resc = createConfigurationContext(mOverrideConfiguration);            mResources = resc.getResources();            return mResources;        }    }

It is mainly implemented in Context. It is estimated that native code is the only way to know how to implement it.

The problem of screen resolution is introduced here first.