Dynamically set the layoutinflater of the layout

Dynamically set the layout LayoutInflater

Recently doing Android project , There is no time to start from scratch , Most of the knowledge points can only be accumulated at the same time . Today, when writing the layout of a requirement, we are Kato Use... At the suggestion of classmates RecyclerView To achieve , Come into contact with during the coding process LayoutInflater This thing , It is also the first contact , Sort out relevant knowledge points .

What is? LayoutInflater

LayoutInflater It's a Is used to xml The layout file is loaded as View perhaps ViewGroup Tools for objects , We can call it ** Layout loader **.

take layout Of xml The layout file is instantiated as View Class object ,LayoutInflater Is similar to findViewById(), The difference is LayoutInflater It's used to find layout Under folder xml Layout file , And instantiate ！ and findViewById() Is to find a specific one xml The details are as follows widget Control ( Such as :Button,TextView etc. ).

Access method

LayoutInflater Itself is an abstract class , Not directly through new To get its instance .

Code up ：

The first method

LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

The second method

LayoutInflater inflater = LayoutInflater.from(context); 

The third method

//  stay Activity Internal calls getLayoutInflater() Method 

These three ways are essentially the same , You can see it in the source code ：

public static LayoutInflater from(Context context) {
    LayoutInflater LayoutInflater =
            (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    if (LayoutInflater == null) {
        throw new AssertionError("LayoutInflater not found.");
    }
    return LayoutInflater;
}

stay Activity Internal calls getLayoutInflater Method actually calls PhoneWindow Of mLayoutInflater：

public PhoneWindow(Context context) {
    super(context);
    mLayoutInflater = LayoutInflater.from(context);
}

These methods actually lead to the same goal , All by calling Context Of getSystemService Method to get .

What you get is PhoneLayoutInflater This implementation class .

public class Policy implements IPolicy {
    ...
    public LayoutInflater makeNewLayoutInflater(Context context) {
        return new PhoneLayoutInflater(context);
    }
}    

Instantiation View Class object

Instantiation LayoutInflater after , will layout Of xml The layout file is instantiated as View Class object .

View view=inflater.inflate(R.layout.ID, null);

inflate Method

Click to enter sdk Source code , You can find inflate Methods have the following overloaded methods ：

The values they return are View object .

among public View inflate (int resource, ViewGroup root) Most commonly used .

Sample code ：

LayoutInflater inflater = (LayoutInflater)getSystemService(LAYOUT_INFLATER_SERVICE); 
View view = inflater.inflate(R.layout.custom, (ViewGroup)findViewById(R.id.test));   
//EditText editText = (EditText)findViewById(R.id.content);// error 
EditText editText = (EditText)view.findViewById(R.id.content);

The second parameter is specified ViewGroup root, Of course, you can set it to null value .

inflate Method parameter relationship

• root != null, attachToRoot == true The incoming layout will be loaded as a View And as a child View Add to root in , Eventually return root; And the root node of this layout android:layout_xxx Parameters will be parsed to set View Size ;
• root == null, attachToRoot meaningless When root It's empty time ,attachToRoot No matter what it is, it doesn't make sense . At this point, the passed in layout will be loaded into a View And return directly ; Layout root View Of android:layout_xxx Attributes are ignored , namely android:layout_xx Attributes can only be attached to a ViewGroup In order to take effect ;
• root != null, attachToRoot == false The incoming layout will be loaded as a View And return directly . Layout root View Of android:layout_xxx The property will be resolved to LayoutParams And set it in View On , here root Only used to set the layout root View The size and location of .

load xml The principle of layout

Start at the root node , Recursive parsing xml Each node of .

The process of recursion at each step is ： By node name （ Full class name ）, Use ClassLoader Create an instance of the corresponding class , That is to say View, then , Put this View Add to its upper nodes （ Father View）.

At the same time, the corresponding xml The attributes of the node are View Properties of . Each level of nodes will be generated one by one View, And according to View The hierarchy of add To the corresponding immediate parent View（ Upper node ） in , Finally, it returns a child that contains all the parsed results View The layout root of View.

Reference material

• Knowledge point ： Dynamic layout LayoutInflater
• Official documents
• understand Android Medium LayoutInflater

Sharing plans

Blog content will be synchronized to Tencent cloud + Community , Invite everyone to join us ：https://cloud.tencent.com/

license agreement

In this paper A signature - Noncommercial use - Share in the same way 4.0 The international license agreement , Reprint please indicate the source .