Question

I want to know how the LayoutParams will work on LayoutInflator. And what is difference between:

LinearLayout childLayout=(LinearLayout)inflater.inflate(R.layout.childitemlayout, null); //FIRST WAY
LinearLayout childLayout=(LinearLayout)inflater.inflate(R.layout.childitemlayout, container,false); //SECOND WAY

Because, both methods gives me different result.
Actually second inflate method are gives me correct result for both child layout change, but First method will gives me different result.

Here is my code:

MainActivity.Java

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        LinearLayout mainLayout=(LinearLayout)findViewById(R.id.mainLayout);
        LayoutInflater inflater=LayoutInflater.from(getApplicationContext());
        for(int i=0;i<10;i++){
            LinearLayout childLayout=(LinearLayout)inflater.inflate(R.layout.childitemlayout, null); //First WAY
//          LinearLayout childLayout=(LinearLayout)inflater.inflate(R.layout.childitemlayout, mainLayout,false);  //SECOND WAY
            mainLayout.addView(childLayout);
        }
    }


main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/mainLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal" >

</LinearLayout>


childitemlayout.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="80dp"
    android:layout_height="80dp"
    android:orientation="vertical" 
    android:background="#525f67">

    <TextView android:id="@+id/btn"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:text="Button"
            android:gravity="center"
            />


</LinearLayout>  <!-- Both ways gives different result  --> 


<!-- 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="vertical" 
    android:background="#525f67">

    <TextView android:id="@+id/btn"
            android:layout_width="80dp"
            android:layout_height="80dp"
            android:text="Button"
            android:gravity="center"
            />


</LinearLayout> Both method gives SAME result   -->  

Answer 1

The main difference between the two inflate() methods is the second parameter(the ViewGroup parameter) and its use in setting the proper LayoutParams for the root view of the inflated layout file. This is important because the LayoutParams keep various layout attributes of the view(like width, height, positioning rules etc) and are required so the parent of that view can properly show the view.

The first method basically says: build the hierarchy view from this layout file but don’t assign LayoutParams to the root of the inflated hierarchy(maybe because the parent isn’t know yet), also don’t attach the inflated view to a parent.

The second inflate method says: build the hierarchy view from this layout file and also assign the proper LayoutParams(based on the second parameter given to the inflate method) to the root of the inflated hierarchy, also don’t attach the inflated view to a parent.

In the first case, the root of the inflated layout file(R.layout.childitemlayout) will not have any LayoutParams set on it(the inflate method didn’t assign any because the second parameter is null and it doesn’t know which type of LayoutParams to generate), so your fixed width/height values are lost. Later when you’ll do mainLayout.addView(childLayout); the mainLayout will check the LayoutParams of the childLayout, see that those are null and will automatically set an instance of the LayoutParams(using its generateDefaultLayoutParams() method). This method, in the particular case of a horizontal LinearLayout, will return an instance of LayoutParams where the width/height will be set to WRAP_CONTENT. So your childLayout will end up with WRAP_CONTENT as its size instead of the fixed values you set on them.

In the second case, the inflate method sees that you suggested the LinearLayout mainLayout as the ViewGroup used for generating the LayoutParams. This means that the fixed values(that you used for the width/height) retrieved from the layout file can be stored in a proper instance of the LayoutParams. When you’ll do mainLayout.addView(childLayout);, mainLayout will see that childLayout has the proper LayoutParams instance(which has the values used in the layout file) and doesn’t call its generateDefaultLayoutParams().