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Dialogs

last modified November 26, 2012

In this chapter of the Android development tutorial we talk about dialogs. We discuss the Android AlertDialog.

A dialog is defined as a conversation between two or more persons. In a computer application a dialog is a window which is used to “talk” to the application. A dialog is used to input data, modify data, change the application settings etc.

An AlertDialog is a dialog used to display information or to receive data. It can display one, two, or three buttons. It is created with a Builder subclass.

Displaying a message

We use the AlertDialog to display a message. In the example, we do not need to modify the manifest file.

main.xml

<?xml version=“1.0” encoding=“utf-8”?> <LinearLayout xmlns:android=“http://schemas.android.com/apk/res/android" android:orientation=“vertical” android:layout_width=“fill_parent” android:layout_height=“fill_parent” >

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="10dip"
    android:onClick="onClicked"
    android:text="@string/btn_label" />

</LinearLayout>

In the main.xml layout file, we have a Button widget. This button displays an AlertDialog.

strings.xml

<?xml version=“1.0” encoding=“utf-8”?> <resources> <string name=“app_name”>DisplaySize</string> <string name=“btn_label”>Show</string> </resources>

This is strings.xml file.

MainActivity.java

package com.zetcode.displaysize;

import android.app.Activity; import android.os.Bundle; import android.view.View; import android.graphics.Point; import android.app.AlertDialog; import android.content.DialogInterface; import android.view.WindowManager; import android.view.Display;

public class MainActivity extends Activity {
@Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); }

public void onClicked(View view)
{
    Point p = getDisplaySize();

    AlertDialog ad = new AlertDialog.Builder(this).create();

    ad.setTitle("Display size");
    String msg = String.format("Width:%d, Height:%d", p.x, p.y);
    ad.setMessage(msg);
    ad.setIcon(android.R.drawable.ic_dialog_info);

    ad.setButton("OK", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int which) {
            dialog.cancel();
        }
    });

    ad.show();     
}

public Point getDisplaySize()
{
    WindowManager wm = (WindowManager) getSystemService(WINDOW_SERVICE);
    Display ds = wm.getDefaultDisplay();

    Point p = new Point();
    ds.getSize(p);

    return p;
}

}

We use the AlertDialog to display the size of the display.

Point p = getDisplaySize();

In the custom getDisplaySize() method, we determine the size of the display.

AlertDialog ad = new AlertDialog.Builder(this).create();

An instance of the AlertDialog is created.

ad.setTitle(“Display size”); String msg = String.format(“Width:%d, Height:%d”, p.x, p.y); ad.setMessage(msg); ad.setIcon(android.R.drawable.ic_dialog_info);

We set a title, message and an icon for the dialog.

ad.setButton(“OK”, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int which) { dialog.cancel(); } });

We add a button to the dialog. When we click on the OK button, the dialog is closed.

ad.show();

The show() method shows the dialog.

WindowManager wm = (WindowManager) getSystemService(WINDOW_SERVICE); Display ds = wm.getDefaultDisplay();

We get the default display.

Point p = new Point(); ds.getSize(p);

We find out the size of the display with the getSize() method.

Figure: AlertDialog showing the size of the display

Receiving data

The second example uses the AlertDialog to receive data from a user. The dialog will ask a user for his name. It will then display the input in a TextView widget.

The manifest file is not modified.

main.xml

<?xml version=“1.0” encoding=“utf-8”?> <LinearLayout xmlns:android=“http://schemas.android.com/apk/res/android" android:orientation=“vertical” android:layout_width=“fill_parent” android:layout_height=“fill_parent” >

<Button
    android:id="@+id/btnId"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="10dip"
    android:onClick="onClicked"
    android:text="@string/btn_label" />   
    
<TextView
    android:id="@+id/tvId"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content" />

</LinearLayout>

This is main.xml file. We have a Button widget and a TextView widget. The button will show the dialog window. The TextView will receive the input text from the dialog.

strings.xml

<?xml version=“1.0” encoding=“utf-8”?> <resources> <string name=“app_name”>InputDialog</string> <string name=“btn_label”>Show dialog</string> </resources>

This is the strings.xml resource file.

MainActivity.java

package com.zetcode.input;

import android.app.Activity; import android.os.Bundle; import android.app.AlertDialog; import android.view.View; import android.widget.EditText; import android.widget.TextView; import android.content.DialogInterface;

public class MainActivity extends Activity { private TextView tv;

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

    tv = (TextView) findViewById(R.id.tvId);
}

public void onClicked(View view)
{
    AlertDialog.Builder ad = new AlertDialog.Builder(this);

    ad.setTitle("Input");
    ad.setMessage("Enter your name");

    final EditText input = new EditText(this);
    ad.setView(input);

    ad.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
    public void onClick(DialogInterface dlg, int which) {
        String val = input.getText().toString();
        String msg = String.format("Hello %s!", val);
        tv.setText(msg);
      }
    });

    ad.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
      public void onClick(DialogInterface dlg, int which) {
        dlg.cancel();
      }
    });

    ad.show();
}

}

Clicking on the button widget will display the AlertDialog. It has an EditText to receive the input from a user.

AlertDialog.Builder ad = new AlertDialog.Builder(this);

ad.setTitle(“Input”); ad.setMessage(“Enter your name”);

We set a title and a message for the dialog.

final EditText input = new EditText(this); ad.setView(input);

We add the EditText widget to the dialog.

ad.setPositiveButton(“Ok”, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dlg, int which) { String val = input.getText().toString(); String msg = String.format(“Hello %s!”, val); tv.setText(msg); } });

Clicking on the OK button of the dialog, we get the text from the EditText widget. The text used to format a greeting which is set to the TextView.

ad.setNegativeButton(“Cancel”, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dlg, int which) { dlg.cancel(); } });

Clicking on the Cancel button will dismiss the dialog.

Figure: Receiving input

In this chapter of the Android development tutorial, we have shown two cases of the AlertDialog.

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