public View(Context context, @Nullable AttributeSet attrs, int defStyleAttr, int defStyleRes) {



}



```

1. View constructor in source code

Through the comments of the source code, we can see that:

1. If the view is new in Java code, call the first constructor – > View (context);

2. If the view is declared in xml, the second constructor – > View (context, attributeset) is called.

2, Android coordinate system

===========================================================================

The Android coordinate system is different from the mathematical coordinate system, which is defined as follows:

• The upper left corner of the screen is the coordinate origin.

• To the right is the increasing direction of the x-axis.

• Downward is the y-axis increasing direction.

See the following figure for details:

3, View location

========================================================================

The position of View is relative to the parent control and is determined by four vertices, as shown in figure A, B, C and D:

There are four parameters to determine the position of the View: Top, Bottom, Left and Right:

• Top: the distance from the upper left corner of the child View to the top of the parent View.

• Left: the distance from the upper left corner of the child View to the left of the parent View.

• Bottom: the distance from the lower right corner of the child View to the top of the parent View.

• Right: the distance from the lower right corner of the child View to the left of the parent View

See the following figure for details:

4, How to get the View location

=============================================================================

The position of View is obtained through getTop(), getLeft(), getBottom(), and getRight() functions.

Here I write a small example to demonstrate the four methods, as follows: (get the location of the internal sub View)

Because it is to demonstrate the position of the View, I use the absolute layout here, and the size unit is px. The specific layout is as follows:

<?xml version="1.0" encoding="utf-8"?>

<AbsoluteLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:app="http://schemas.android.com/apk/res-auto"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    tools:context=".MainActivity">



    <RelativeLayout

        android:id="@+id/rl_1"

        android:layout_width="600px"

        android:layout_height="600px"

        android:layout_x="200px"

        android:layout_y="200px"

        android:background="@color/colorPrimaryDark">



        <View

            android:id="@+id/view"

            android:layout_width="300px"

            android:layout_height="300px"

            android:layout_centerInParent="true"

            android:background="@color/colorAccent" />



    </RelativeLayout>



</AbsoluteLayout>

We now use four methods to obtain the location of the View. The specific code is as follows:

public class CoordinateActivity extends AppCompatActivity {



    private View mView;



    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_coordinate);



        rl1 = findViewById(R.id.rl_1);

        mView = findViewById(R.id.view);



    }



    @Override

    protected void onResume() {

        super.onResume();



        new Handler().postDelayed(new Runnable() {

            @Override

            public void run() {

                MyLogUtils.i(mView.getTop() + "--Top --mView");

                MyLogUtils.i(mView.getBottom() + "--Bottom --mView");

                MyLogUtils.i(mView.getLeft() + "--Left --mView");

                MyLogUtils.i(mView.getRight() + "--Right --mView");

                MyLogUtils.i(mView.getX() + "--X --mView");

                MyLogUtils.i(mView.getY() + "--Y --mView");

            }

        }, 200);

    }

}

The printing results are as follows:

The coordinates of the outermost purple View are (200200) and the size is 600px. Inside it, a sub View with the size of 300px is located in its center, so the above printing results are completely correct.

last

Considering the length of the article, I have made these questions and answers, as well as the problems I have encountered in my interview for many years and some interview materials into PDF files

CodeChina open source project: Android learning notes summary + mobile architecture Video + big factory interview real questions + project actual combat source code

last

Considering the length of the article, I have made these questions and answers, as well as the problems I have encountered in my interview for many years and some interview materials into PDF files

CodeChina open source project: Android learning notes summary + mobile architecture Video + big factory interview real questions + project actual combat source code

[external chain picture transferring... (img-aKhx2OAp-1630646026532)]

[external chain pictures are being transferred... (img-KOgZr8kK-1630646026533)]

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