Tuesday, July 17, 2012

Error of getLocationInWindow() and getLocationOnScreen()

The View class provide the methods to computes the coordinates:

In my experience, the returned x location is correct, but the y location is always error with a fixed offset. The offset various depends on devices and configuration.

To correct it, we can get the offset using the code, after view displayed:
DisplayMetrics displayMetrics = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
int offsetY = displayMetrics.heightPixels - mainScreen.getMeasuredHeight();


offset of getLocationInWindow() and getLocationOnScreen()


package com.example.androidoffsetgetlocation;

import android.os.Bundle;
import android.app.Activity;
import android.util.DisplayMetrics;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;

public class MainActivity extends Activity {
 
 LinearLayout mainScreen;
 ImageView object;
 TextView textOnCreate, textOnWindowFocusChanged;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        mainScreen = (LinearLayout)findViewById(R.id.mainscreen);
        object = (ImageView)findViewById(R.id.object);
        textOnCreate = (TextView)findViewById(R.id.textview1);
        textOnWindowFocusChanged = (TextView)findViewById(R.id.textview2);
  
  readLocation(textOnCreate, "onCreate()");
    }

 @Override
 public void onWindowFocusChanged(boolean hasFocus) {
  // TODO Auto-generated method stub
  super.onWindowFocusChanged(hasFocus);
  
  readLocation(textOnWindowFocusChanged, "onWindowFocusChanged()");
 }
 
 private void readLocation(TextView tv, String status){
  DisplayMetrics displayMetrics = new DisplayMetrics();
  getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
  int offsetX = displayMetrics.widthPixels - mainScreen.getMeasuredWidth();
  int offsetY = displayMetrics.heightPixels - mainScreen.getMeasuredHeight();
        
        int[] locationInWindow = new int[2];
  object.getLocationInWindow(locationInWindow);
  int[] locationOnScreen = new int[2];
  object.getLocationOnScreen(locationOnScreen);
  
  tv.setText(
    "\n" + status +"\n"
    + "getLocationInWindow() - " + locationInWindow[0] + " : " + locationInWindow[1] + "\n"
    + "getLocationOnScreen() - " + locationOnScreen[0] + " : " + locationOnScreen[1] + "\n"
    + "Offset x: y - " + offsetX + " : " + offsetY);
  
 }

}


<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" 
    android:orientation="vertical"
    android:id="@+id/mainscreen">
     
    <ImageView
        android:id="@+id/object"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/ic_launcher"/>
    <TextView
        android:id="@+id/textview1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
    <TextView
        android:id="@+id/textview2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>

</LinearLayout>



2 comments:

Kuan Shu said...

Thank you, but how did you know that? since i find nowhere in the official documentation!

Andr.oid Eric said...

Hello Kuan Shu,

I forgot the history.