Android self-defined component Family "1"-define View and ViewGroup

Last Update:2017-07-01 Source: Internet

Author: User

Developer on Alibaba Coud: Build your first app with APIs, SDKs, and tutorials on the Alibaba Cloud. Read more ＞

The view class is the parent of viewgroup, and ViewGroup has all the properties of the VIEW. ViewGroup is primarily used as a container for VIEW. Take the view as your own child and manage it. Of course the child can also be a viewgroup type.The view class is typically used for paint operations, overriding its OnDraw method, but it cannot include other components, without the AddView (view view) method.ViewGroup is a component container that can include no matter what component, but must override OnLayout(boolean changed,int l,int t,int r,int b) and onmesure (int Widthmesurespec,int HEIGHTMESURESPEC) Method. Otherwise , adding components in ViewGroup is not displayed. " /strong> <pre code_snippet_id="299151" snippet_file_name="blog_20140418_1_3051849" name="code" class="java">package Com.example.testrefreshview;import Android.app.activity;import Android.content.context;import Android.os.bundle;import Android.view.viewgroup;import Android.widget.button;import android.widget.TextView; public class Mainactivity extends Activity {@Overrideprotected void onCreate (Bundle Savedinstancestate) {super.oncreate (savedinstancestate); Setcontentview (new Myviewgroup (this));} public class Myviewgroup extends ViewGroup {public myviewgroup (context Context) {super (context); Button button1 = New button (context); Button1.settext ("button1"); Button button2 = New button (context); Button2.settext ("button2"); TextView TextView = new TextView (context); textview.settext ("TextView"); addview (button1); addview (button2); AddView ( textView);} @Overrideprotected void onlayout (boolean arg0, int arg1, int arg2, int arg3,int arg4) {} }}</pre>The layout of view (int left,int Top,int Right,int Bottom) method is responsible for placing the view in the specified position, so if we define the viewgroup::o in our own Nlayout iterates through each child view and assigns its position with View.layout (). Each child view also calls onlayout, which makes up a recursive call process If you override the OnDraw method in Viewgroup. Need to call This.setwillnodraw (flase) in the constructor method; The overridden OnDraw (Canvas Cancas) method is not called at this Time. otherwise, the OnDraw (canvas Canvas) method is not Called.Change the code above to show it.<pre code_snippet_id="299151" snippet_file_name="blog_20140418_2_1907580" name="code" class="java">Package Com.example.testrefreshview;import Android.app.activity;import Android.content.context;import Android.os.bundle;import Android.view.view;import Android.view.viewgroup;import Android.widget.Button;import Android.widget.textview;public class Mainactivity extends Activity {@Overrideprotected void OnCreate (Bundle Savedinstancestate) {super.oncreate (savedinstancestate); setcontentview (new myviewgroup (this));} public class Myviewgroup extends ViewGroup {public myviewgroup (context Context) {super (context); Button button1 = New button (context); Button1.settext ("button1"); Button button2 = New button (context); Button2.settext ("button2"); TextView TextView = new TextView (context); textview.settext ("TextView"); addview (button1); addview (button2); AddView ( textView);} @Overrideprotected void onlayout (boolean arg0, int arg1, int arg2, int arg3,int arg4) {int childCount = Getchildcount (); in T left = 0;int top = 10;for (int i = 0; i < childCount; i++) {View child = Getchildat (i); child.layout (left, top,Left + +, Top + +); top + + 70;}}} </pre>Look at the code again:<pre code_snippet_id="299151" snippet_file_name="blog_20140418_3_2398731" name="code" class="java"><pre code_snippet_id="299151" snippet_file_name="blog_20140418_3_2398731" name="code" class="java">@Override protected void onmeasure (int widthmeasurespec, int heightmeasurespec) { int childCount = Getchildcount (); Set the size of the viewgroup int specsize_width = measurespec.getsize (widthmeasurespec); int specsize_height = measurespec.getsize (heightmeasurespec); Setmeasureddimension (specsize_width, specsize_height); for (int i = 0; i < childCount; i++) { View childview = Getchildat (i); Childview.measure (a);} } </pre></pre>By overriding the Onmeasure method, you can specify a size for viewgroup, and you can specify the size for each child view by Traversing. Adding the above code to your own definition ViewGroup assigns the displayed width height to each child view in Viewgroup. Let's make the sub-view move up. Add code such as the Following:<pre code_snippet_id="299151" snippet_file_name="blog_20140418_4_1777067" name="code" class="java"><pre code_snippet_id="299151" snippet_file_name="blog_20140418_4_1777067" name="code" class="java">public boolean ontouchevent (motionevent ev) {final float y = ev.gety (), switch (ev.getaction ()) {case motionevent.action_ Down:mlastmotiony = y;break; Case MotionEvent.ACTION_MOVE:int Detay = (int) (mlastmotiony-y); mlastmotiony = Y;scrollby (0, detay); Case MotionEvent.ACTION_UP:break;} Return true;}</pre></pre>In the above using a Scrollby method, open the official API can see the view class has such as the following two methods: Both of these functions seem to be mobile views. So what's the difference between them? With this question we look downfirst, we have to make it clear that there is no boundary on the Android view view, and that canvas has no boundaries , just that we do some work on the canvas object by drawing a specific view. For example: translate (pan), clipRect (cut), etc., in order to achieve our requirements for the canvas object Drawing. We can refer to such borderless views as " view coordinates "-----which are not restricted by physical screens. Usually we understand that a layout file is only the display area of the view, beyond which the display area will not be displayed in the parent view of the area, accordingly, we can call such a bounded view of the layout coordinates ------the parent view to the child view assigned layout ( Layout) Size. also, The starting coordinate of a view on the screen is at the beginning of the view Coordinates. For example, as seen in The. Because layout coordinates can only display a specific piece of content. So we only have the coordinate origin of the moving layout coordinates to show the coordinates of the view wherever they are located.<pre code_snippet_id="299151" snippet_file_name="blog_20140418_5_7808115" name="code" class="html"><pre code_snippet_id="299151" snippet_file_name="blog_20140418_5_7808115" name="code" class="html"><linearlayout xmlns:android= "http://schemas.android.com/apk/res/android" android:layout_width= "fill_ Parent " android:layout_height=" fill_parent " android:orientation=" vertical " android:background=" # 888888 "><textview android:id=" @+id/txt " android:layout_width=" 300dip " android:layout_height= "120dip" android:background= "#cccccc" android:text= "textview"/><button android:id= "@+id/ BTN " android:layout_width=" wrap_content " android:layout_height=" wrap_content " android:text=" Button "/></linearlayout></pre></pre> When I click the button to trigger an event such as the Following: After triggering the Click event in the Code above, Textview.scrollto ( -200, -100) is run, and the meaning of the two parameters in ScrollTo is not the coordinate Position. Instead of the offset from the position of the view coordinate , if we want to move to the position of (200,100), the offset is (0,0)-(200,100) = (-200. -100).If we replace the above code with scrollby, we will find that the TextView will move out of the visible interface after clicking multiple buttons, because Scrollby is offset from our current coordinates .Let's look at how these two methods are implemented in the source code:<pre code_snippet_id="299151" snippet_file_name="blog_20140418_6_3499993" name="code" class="java"><pre code_snippet_id="299151" snippet_file_name="blog_20140418_6_3499993" name="code" class="java"> /** * Set The scrolled position of your VIEW. This would cause a call to * {@link #onScrollChanged (int, int, int, int)} and the view would be * Invalidated. * @param x position to scroll to * @param y the y position to scroll to */public void ScrollTo (int x, i NT Y) { If (mscrollx! = x | | mscrolly! = y) { int oldx = mscrollx; int OldY = mscrolly; MSCROLLX = x; mscrolly = y; Invalidateparentcaches (); onscrollchanged (mscrollx, mscrolly, oldx, oldY); If (!awakenscrollbars ()) { invalidate (true);}}} </pre></pre>can see MSCROLLX = x; mscrolly = y;<pre code_snippet_id="299151" snippet_file_name="blog_20140418_7_4306788" name="code" class="java"><pre code_snippet_id="299151" snippet_file_name="blog_20140418_7_4306788" name="code" class="java"> /** * Move The scrolled position of your VIEW. This would cause a call to * {@link #onScrollChanged (int, int, int, int)} and the view would be * Invalidated. * @param x The amount of pixels to scroll by horizontally * @param y the amount of pixels to scroll by vertically */public void Scrollby (int x, int y) { scrollTo (mscrollx + x, mscrolly + y); }</pre></pre>able to see Mscrollx + x, mscrolly + y;Mscrollx and mscrolly are the current offsets relative to the view Coordinates. Android self-defined component Family "1"-define View and ViewGroup

This article is an English version of an article which is originally in the Chinese language on aliyun.com and is provided for information purposes only. This website makes no representation or warranty of any kind, either expressed or implied, as to the accuracy, completeness ownership or reliability of the article or any translations thereof. If you have any concerns or complaints relating to the article, please send an email, providing a detailed description of the concern or complaint, to info-contact@alibabacloud.com. A staff member will contact you within 5 working days. Once verified, infringing content will be removed immediately.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

Get Started for Free

Sales Support

1 on 1 presale consultation

Chat Contact Sales
After-Sales Support

24/7 Technical Support 6 Free Tickets per Quarter Faster Response

Open a Ticket
Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.

Learn More

Android self-defined component Family "1"-define View and ViewGroup

Contact Us

What's Trending

Top 10 Tags

Top 10 Keywords

A Free Trial That Lets You Build Big!

Sales Support

After-Sales Support

Android self-defined component Family "1"-define View and ViewGroup

Contact Us

What's Trending

Top 10 Tags

Top 10 Keywords

Trending Topic

A Free Trial That Lets You Build Big!

Sales Support

After-Sales Support