UiAutomator源码学习（1）-- UiDevice

 device = UiDevice.getInstance(getInstrumentation());
 device.pressHome();

    // Bring up the default launcher by searching for a UI component
    // that matches the content description for the launcher button.
 UiObject allAppsButton = device
            .findObject(new UiSelector().description("Apps"));

    // Perform a click on the button to load the launcher.
 allAppsButton.clickAndWaitForNewWindow();

 /** Private constructor. Clients should use {@link UiDevice#getInstance(Instrumentation)}. */
    private UiDevice(Instrumentation instrumentation) {
        mInstrumentation = instrumentation;
        UiAutomation uiAutomation = instrumentation.getUiAutomation();
        mUiAutomationBridge = new InstrumentationUiAutomatorBridge(
                instrumentation.getContext(), uiAutomation);
        // Enable multi-window support for API level 21 and up
        if (UiDevice.API_LEVEL_ACTUAL >= Build.VERSION_CODES.LOLLIPOP) {
            // Subscribe to window information
            AccessibilityServiceInfo info = uiAutomation.getServiceInfo();
            info.flags |= AccessibilityServiceInfo.FLAG_RETRIEVE_INTERACTIVE_WINDOWS;
            uiAutomation.setServiceInfo(info);
        }
    }
    /**
     * Retrieves a singleton instance of UiDevice
     *
     * @return UiDevice instance
     */
    public static UiDevice getInstance(Instrumentation instrumentation) {
        if (sInstance == null) {
            sInstance = new UiDevice(instrumentation);
        }
        return sInstance;
    }

 /**
     * Returns the display size in dp (device-independent pixel)
     *
     * The returned display size is adjusted per screen rotation. Also this will return the actual
     * size of the screen, rather than adjusted per system decorations (like status bar).
     *
     * @return a Point containing the display size in dp
     */
    public Point getDisplaySizeDp() {
        Tracer.trace();
        Display display = getAutomatorBridge().getDefaultDisplay();
        Point p = new Point();
        display.getRealSize(p);
        DisplayMetrics metrics = new DisplayMetrics();
        display.getRealMetrics(metrics);
        float dpx = p.x / metrics.density;
        float dpy = p.y / metrics.density;
        p.x = Math.round(dpx);
        p.y = Math.round(dpy);
        return p;
    }

getDisplaySizeDp()方法返回的是一个以dp为单位的坐标点。同样可以获取设备的宽度或者高度：

  /**
     * Gets the width of the display, in pixels. The width and height details
     * are reported based on the current orientation of the display.
     * @return width in pixels or zero on failure
     */
    public int getDisplayWidth() {
        Display display = getDefaultDisplay();
        Point p = new Point();
        display.getSize(p);
        return p.x;
    }

/**
     * Returns a UiObject which represents a view that matches the specified selector criteria.
     *
     * @param selector
     * @return UiObject object
     */
    public UiObject findObject(UiSelector selector) {
        return new UiObject(this, selector);
    }

   /**
     * Simulates a short press on the HOME button.
     * @return true if successful, else return false
     * @since API Level 16
     */
    public boolean pressHome() {
        Tracer.trace();
        waitForIdle();
        return getAutomatorBridge().getInteractionController().sendKeyAndWaitForEvent(
                KeyEvent.KEYCODE_HOME, 0, AccessibilityEvent.TYPE_WINDOW_CONTENT_CHANGED,
                KEY_PRESS_EVENT_TIMEOUT);
    }

 /**
     * Perform a click at arbitrary coordinates specified by the user
     *
     * @param x coordinate
     * @param y coordinate
     * @return true if the click succeeded else false
     * @since API Level 16
     */
    public boolean click(int x, int y) {
        Tracer.trace(x, y);
        if (x >= getDisplayWidth() || y >= getDisplayHeight()) {
            return (false);
        }
        return getAutomatorBridge().getInteractionController().clickNoSync(x, y);
    }
    /**
     * Performs a swipe from one coordinate to another using the number of steps
     * to determine smoothness and speed. Each step execution is throttled to 5ms
     * per step. So for a 100 steps, the swipe will take about 1/2 second to complete.
     *
     * @param startX
     * @param startY
     * @param endX
     * @param endY
     * @param steps is the number of move steps sent to the system
     * @return false if the operation fails or the coordinates are invalid
     * @since API Level 16
     */
    public boolean swipe(int startX, int startY, int endX, int endY, int steps) {
        Tracer.trace(startX, startY, endX, endY, steps);
        return getAutomatorBridge().getInteractionController()
                .swipe(startX, startY, endX, endY, steps);
    }