Common View Controls

TextView

A TextView is used to display text.

<TextView
android:id="@+id/tvText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Message" />

We use the id of the view to get the view in e.g. an activity that needs to update the text.

TextView tv = (TextView) parentView.findViewById(R.id.tvText);
tv.setText("New text");

If the text is not dynamic, you should define the text in res/values/strings.xml so that it can be internationalized.

EditText

When you need text input from the user, you can use the EditText control.

<EditText
    android:id="@+id/search"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:hint="@string/search_hint"
    android:inputType="text"
    android:imeOptions="actionSend" />

EditText editText = (EditText) findViewById(R.id.search);
editText.setOnEditorActionListener(new OnEditorActionListener() {
    @Override
    public boolean onEditorAction(TextView v, int actionId, KeyEvent event) {
        boolean handled = false;
        if (actionId == EditorInfo.IME_ACTION_SEND) {
            sendMessage();
            handled = true;
        }
        return handled;
    }
});

Button

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/button_text"
    ... />

Button button = (Button) findViewById(R.id.button_send);
button.setOnClickListener(new View.OnClickListener() {
    public void onClick(View v) {
        // Do something in response to button click
    }
});

ImageView

Images files are referred to as drawables. They are put in folders for each device resolution inside the res directory, e.g. res/drawable-xxhdpi. The runtime chooses which image to use on each device. @drawable/my_image refers to the image my_image.png located in all the drawable folders you are providing.

<ImageView
    android:id="@+id/image"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:scaleType="center"
    android:src="@drawable/my_image" />