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This article is about how to customize View for Android. Xiaobian thinks it is quite practical, so share it with everyone for reference. Let's follow Xiaobian and have a look.

There are three ways to implement custom controls: composite controls, self-drawn controls, and inherited controls.

Let's summarize the steps for customizing the View:

1. Custom View Properties

2. Get our custom attributes in the View constructor

[ 3, rewrite onMesure ]

4. Rewrite onDraw

I marked 3 with [], so saying 3 is not necessarily necessary, but of course it needs to be rewritten in most cases.

At present, there is a lot of code about the implementation of this piece. We are here to directly project the code. There are detailed comments in the code. If you don't understand, you can leave a message and ask. Custom title textView listView three very simple small demo

https://github.com/AnyMarvel/CustomView

(Interested parties can start updating later on this project)

The first phase effect picture is shown in the picture (is it very ugly, haha, let's see...):

Instead of analyzing the code here, we will first introduce the basics of custom View.

key methods

I. LayoutInflater.inflate() parameters and their usage

1. There are three ways to get LayoutInflater objects

LayoutInflater inflater=LayoutInflater.from(this);

LayoutInflater inflater=getLayoutInflater();

LayoutInflater inflater=(LayoutInflater)this.getSystemService(LAYOUT_INFLATER_SERVICE);

2. About LayoutInflater class inflate(int resource, ViewGroup root, boolean attachToRoot) The meaning of three parameters

resource: ID of the layout file that needs to be loaded, meaning that the layout file needs to be loaded into the Activity for operation.

root： Inflate() returns a View object. If the third parameter attachToRoot is true, return this root as the root object. Otherwise, just attach the LayoutParams attribute of this root object to the root layout object of the resource object, that is, the outermost View of the layout file resource, such as a LinearLayout or other Layout object.

attachToRoot: whether root is attached to the root view of the layout file

II. constructor instruction

There are a lot of things that are wrong with the way that we do things, but there are a lot of things that are wrong with us.

The first constructor is called when a Custom View instance is directly new in the code. There is no dispute about this.

When Custom View is invoked in an xml layout file, the second constructor is invoked. There's no dispute about that.

When Custom View is invoked in an xml layout file and custom properties are included in the Custom View tag, the second constructor is invoked. That is, by default, only the first two constructors of Custom View will be called, and the third constructor will usually be called voluntarily by ourselves (e.g., calling the third constructor in the second constructor).

Enabled only if the third parameter defStyleAttr is 0, or if no assignment for this defStyleAttr attribute is found in the topic. And this parameter is no longer Attr, but the real style. In fact, this is also a low-level "default theme", that is, when the theme does not declare attribute values, we can actively give a style, use this constructor to define the View, and its theme is the defStyleRes of this definition (it is a dead style, so the priority is lowered).

There are four constructors in the View class that involve multiple parameters,

Context: Online text, this need not be said much

AttributeSet attrs: parameters defined from xml

int defStyleAttr: The attribute with the highest priority in the topic

int defStyleRes: style built into View with second priority

Properties in android can be assigned in multiple places, and the priority involved is:

Xml direct definition> style reference in xml> defStyleAttr > defStyleRes > theme direct definition

For more information, please go to blog.csdn.net/zhao123h/article/details/52210732

III. Paint, Rect, Canvas

Tools are to make it easier for us to draw what we want, here is only a simple introduction, other uses please own Baidu

Canvas class

Can be used to achieve a variety of graphics drawing work, such as drawing lines, rectangles, circles and so on

1. Draw a line: canvas.drawLine();

2. Draw rectangle: canvas.drawRect();

Draw Circle: canvas.drawCircle();

4. Draw characters: canvas.drawText();

5, Draw graphics: canvas.drawBirmap();

Paint class

To draw graphics, you must first adjust the brush, according to their own way to open the master is also starting from the white.

Hair needs to set the relevant properties of the brush

1. setAntiAlias(): Set the sawtooth effect of the brush

setColor(): Sets the color of the brush

3. setARGB(): Set the A, R, G, B values of the brush

setAlpha(): Sets the Alpha value of the brush

5. setTextSize(): Sets the size of the font

setStyle(): Sets the style of the brush (hollow or solid)

7. setStrokeWidth(): Sets the width of the hollow border

getColor(): Gets the color of the brush

Rect (size) class

new Rect(int left, int top, int right, int bottom)

IV. event transfer mechanism

Different controls in Android have slightly different event distribution, interception, and response, mainly because the Activity itself does not have event interception, and the smallest view unit that is not a ViewGroup does not have event distribution and event interception (because it does not have its own child View).

Thank you for reading! About "Android how to customize View" This article is shared here, I hope the above content can be of some help to everyone, so that everyone can learn more knowledge, if you think the article is good, you can share it to let more people see it!

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