android develope

Ref : https://developer.android.com/training/basics/firstapp/building-ui.html


Because the LinearLayout is the root view in the layout, it should fill the entire screen area that's available to the app by setting the width and height to"match_parent". This value declares that the view should expand its width or height to match the width or height of the parent view.

<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="horizontal">
    <EditText android:id="@+id/edit_message"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:hint="@string/edit_message" />
</LinearLayout>

android:hint

This is a default string to display when the text field is empty. Instead of using a hard-coded string as the value, the "@string/edit_message" value refers to a string resource defined in a separate file. Because this refers to a concrete resource (not just an identifier), it does not need the plus sign. However, because you haven't defined the string resource yet, you’ll see a compiler error at first. You'll fix this in the next section by defining the string.

Add String Resources

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By default, your Android project includes a string resource file at res/values/strings.xml. Here, you'll add two new strings.

1. From the res/values/ directory, open strings.xml.
2. Add two strings so that your file looks like this:

   <?xml version="1.0" encoding="utf-8"?>
   <resources>
       <string name="app_name">My First App</string>
       <string name="edit_message">Enter a message</string>
       <string name="button_send">Send</string>
   </resources>