Launcher modification-page tag implementation principle (Code tracking)

When reading this article, you may have seen the 2.1 screen tag (http://gqdy365.iteye.com/blog/897636) on launcher 2.2, using an imageview to display different pictures, take a look at the implementation of the source code in launcher2 in Android. In the drawable folder, you can find a home_arrows_left.xml file with the following content:

<?xml version="1.0" encoding="utf-8"?><level-list xmlns:android="http://schemas.android.com/apk/res/android">    <item android:maxLevel="0" android:drawable="@android:color/transparent" />    <item android:maxLevel="1" android:drawable="@drawable/home_arrows_left_1" />    <item android:maxLevel="2" android:drawable="@drawable/home_arrows_left_2" />    <item android:maxLevel="3" android:drawable="@drawable/home_arrows_left_3" />    <item android:maxLevel="4" android:drawable="@drawable/home_arrows_left_4" /></level-list>

In the launcher. xml file,

<ImageView android:id="@+id/previous_screen"android:layout_width="93dip"                                           android:layout_height="@dimen/button_bar_height"android:layout_gravity="bottom|left"                 android:layout_marginLeft="6dip"android:scaleType="center"                 android:src="@drawable/home_arrows_left"android:onClick="previousScreen"                  android:focusable="true"android:clickable="true" />

This file is referenced, but how is it actually implemented in the code? In the setupviews () method of launcher. Java, there is the code:

 mPreviousView = (ImageView) dragLayer.findViewById(R.id.previous_screen);        mNextView = (ImageView) dragLayer.findViewById(R.id.next_screen);        Drawable previous = mPreviousView.getDrawable();        Drawable next = mNextView.getDrawable();        mWorkspace.setIndicators(previous, next);

Get the image on both sides through code, and then let's take a look at the setindicator () method in workspace. java,

void setIndicators(Drawable previous, Drawable next) {        mPreviousIndicator = previous;        mNextIndicator = next;        previous.setLevel(mCurrentScreen);        next.setLevel(mCurrentScreen);    }

Let's find the definition of mcurrentscreen (73 rows ):

 private int mCurrentScreen;

The defined integer corresponds to maxlevel in home_arrows_left.xml. Different images are displayed on different imageview parameters to mark pages.

In the preceding launcher code, Android: onclick = "previusscreen" registers the imageview click event. In launcher. Java, the corresponding code is as follows:

@SuppressWarnings({"UnusedDeclaration"})    public void previousScreen(View v) {        if (!isAllAppsVisible()) {            mWorkspace.scrollLeft();        }    }    @SuppressWarnings({"UnusedDeclaration"})    public void nextScreen(View v) {        if (!isAllAppsVisible()) {            mWorkspace.scrollRight();        }    }

We continue to track the code of the scrollleft and scrollright () methods in the workspace. Java code:

public void scrollLeft() {        clearVacantCache();        if (mScroller.isFinished()) {            if (mCurrentScreen > 0) snapToScreen(mCurrentScreen - 1);        } else {            if (mNextScreen > 0) snapToScreen(mNextScreen - 1);                    }    }    public void scrollRight() {        clearVacantCache();        if (mScroller.isFinished()) {            if (mCurrentScreen < getChildCount() -1) snapToScreen(mCurrentScreen + 1);        } else {            if (mNextScreen < getChildCount() -1) snapToScreen(mNextScreen + 1);                    }    }

First determine whether to slide to the header, and then jump to the target screen. The snaptoscreen () method code is also in the workspace. The Code is as follows:

private void snapToScreen(int whichScreen, int velocity, boolean settle) {        //if (!mScroller.isFinished()) return;        whichScreen = Math.max(0, Math.min(whichScreen, getChildCount() - 1));                clearVacantCache();        enableChildrenCache(mCurrentScreen, whichScreen);        mNextScreen = whichScreen;        mPreviousIndicator.setLevel(mNextScreen);        mNextIndicator.setLevel(mNextScreen);enableDragLayerChildrenCache();        View focusedChild = getFocusedChild();        if (focusedChild != null && whichScreen != mCurrentScreen &&                focusedChild == getChildAt(mCurrentScreen)) {            focusedChild.clearFocus();        }                final int screenDelta = Math.max(1, Math.abs(whichScreen - mCurrentScreen));        final int newX = whichScreen * getWidth();        final int delta = newX - mScrollX;        int duration = (screenDelta + 1) * 100;        if (!mScroller.isFinished()) {            mScroller.abortAnimation();        }                if (settle) {            mScrollInterpolator.setDistance(screenDelta);        } else {            mScrollInterpolator.disableSettle();        }                velocity = Math.abs(velocity);        if (velocity > 0) {            duration += (duration / (velocity / BASELINE_FLING_VELOCITY))                    * FLING_VELOCITY_INFLUENCE;        } else {            duration += 100;        }        awakenScrollBars(duration);        mScroller.startScroll(mScrollX, 0, delta, 0, duration*2/3);        invalidate();    }

This is the basic process of its implementation.