Customizing a view in Android is a detailed approach _android

The examples in this article describe a way to customize a view in Android. Share to everyone for your reference, specific as follows:

Android Custom View implementation is relatively simple, nothing more than inheriting the parent class, and then overloaded methods, even so, in the actual coding will inevitably encounter some pits, I have encountered some of my problems and solutions summed up, I hope that the vast number of friends to help.

Note ① when defining layout with XML, Root element is best to use the merge

When we need to inherit a more complex viewgroup (more of LinearLayout, relativelayout), we usually write the layout with XML, and then inflate the XML file that defines layout in the custom view class.

First, create a new class file named Mylayout that resolves the xml file that is later defined in the Init method.

/**
 * Created by Liangfei on 4/14/15.
 * * Public
class Mylayout extends LinearLayout {public
  mylayout (context) {
    super (context);
    Init ();
  }
  private void Init () {
    setorientation (VERTICAL);
    View Rootview = Inflate (GetContext (), r.layout.my_layout, this);
    ((TextView) Rootview.findviewbyid (R.id.title)). SetText ("Mylayout");
    ((TextView) Rootview.findviewbyid (R.id.desc)). SetText ("A Customized Layout");
  }

A new layout file named My_layout is created and the Root element is set to merge.

<?xml version= "1.0" encoding= "Utf-8"?> <merge xmlns:android=
"http://schemas.android.com/apk/res/" Android ">
  <textview
    android:id=" @+id/title "
    android:textsize=" 16sp "
    android:layout_width = "Wrap_content"
    android:layout_height= "wrap_content"/>
  <textview android:id=
    "@+id/desc"
    Android:layout_width= "Wrap_content"
    android:layout_height= "wrap_content"/>
</merge>

Use the Monitor tools included with the Android SDK to view the layout information for the runtime.

The top floor is a framelayout, then a linearlayout, with two textview inside, and you can see that the layout is not redundant.

But what happens if you change the Root element to LinearLayout?

<?xml version= "1.0" encoding= "Utf-8"?> <linearlayout xmlns:android=
"http://schemas.android.com/apk/" Res/android "
  android:orientation=" vertical "
  android:layout_width=" wrap_content "
  android:layout_" height= "Wrap_content" >
  <textview
    android:id= "@+id/title"
    android:textsize= "16sp"
    Android : layout_width= "wrap_content" android:layout_height= "wrap_content"/> <textview android:id=
    " @+id/desc "
    android:layout_width=" wrap_content "
    android:layout_height=" wrap_content "/>
</ Linearlayout>

Obviously, after using LinearLayout as Root element, the layout is one more level, which is a factor affecting performance.

Note Dot ② The overloaded subclass constructor to figure out what the parent class did

Start with a bitter lesson from me, when I did this by customizing a button:

/**
 * Created by Liangfei on 4/14/15.
 */Public
class MyButton extends Button {public
  MyButton (context
    , null);
  Public MyButton (context, AttributeSet attrs) {This
    (context, attrs, 0);
  }
  Public MyButton (context, AttributeSet attrs, int defstyleattr) {
    Super (context, attrs, defstyleattr);
    Init ();
  }
}

At first glance it looks like there's no problem, the constructor is invoked correctly, but no matter how I modify the MyButton properties, the display is incorrect.

In fact, the problem is that the button class uses a defstyleattr in the constructor, and my writing ignores this defstyleattr- Com.android.internal.r.attr.buttonstyle, slightly read the source code will know.

@RemoteView Public
class button extends TextView {
    the context, NULL, the public button.
  "Public Button" (context,
  AttributeSet attrs) {The context
    , Attrs, Com.android.internal.r.attr.buttonstyle);
  }
  Public Button (context, AttributeSet attrs, int defstyleattr) {This
    (context, Attrs, defstyleattr, 0);
  } Public
  Button (context, AttributeSet attrs, int defstyleattr, int defstyleres) {
    Super (context, attrs, Defstyleattr, defstyleres);
  }

Later, when I wrote the code, I looked at the source of the parent class and then dared to write, if not sure, honestly wrote the following form.

/**
 * Created by Liangfei on 4/14/15.
 * * Public
class MyButton extends Button {public
  MyButton (context) {
    super);
    Init ();
  }
  Public MyButton (context, AttributeSet attrs) {
    Super (context, attrs);
    Init ();
  }
  Public MyButton (context, AttributeSet attrs, int defstyleattr) {
    Super (context, attrs, defstyleattr);
    Init ();
  }
}

In fact, there are many other pits, such as the height of the Button, after the time to sum up

More interested readers of Android-related content can view the site's topics: "The Overview of Android View View Tips", "Android operation XML Data Skills Summary", "Android programming activity Operation Skills Summary", " Android Resource Operation tips Summary, "Android file Operation Tips", "Android operation SQLite Database Skills Summary", "Android operation JSON format Data Skills summary", "Android Database Operating skills summary", " Android programming development of the SD card operation method Summary, "Android Development introduction and Advanced Course" and "Android Control usage Summary"

I hope this article will help you with the Android program.