Archive for April, 2010

Here is a quick tip for better organisation of your program by grouping all onClickListeners into a simple switch statement.

The problem
If you have lots of buttons or view that you are linking to OnClickListener events you can quickly end up with some cumbersome code. This can be changed very simply by implementing a method in your activity and switching between View ID’s.

Below is an example the typical method for creating an OnClickListener for a View.

final ImageButton Ibutton = (ImageButton) findViewById(R.id.button_1);
Ibutton.setOnClickListener(new OnClickListener() {
	public void onClick(View v) {
		Toast.makeText(testActivity.this, "Button 1 pressed ", Toast.LENGTH_SHORT).show();
	}
});

final ImageButton Ibutton2 = (ImageButton) findViewById(R.id.button_2);
Ibutton2.setOnClickListener(new OnClickListener() {
	 public void onClick(View v) {
		Toast.makeText(testActivity.this, "Button 2 pressed", Toast.LENGTH_SHORT).show();
	}
});

The Solution
We can get our activity to handle the OnClick events itself, we do this we implementing OnClickListener:

public class testActivity extends Activity implements OnClickListener {

If your write this in eclipse you can hover over the error this produces and click Add unimplemented methods to automatically create a stub for the next part.

eclipse auto suggesting to implement the onclicklistener method

We now create our buttons similar to before, but for the setOnClickListener we pass this as an argument, so that our implemented method is called.

ImageButton Ibutton = (ImageButton) findViewById(R.id.button_1);
Ibutton.setOnClickListener(this);      

ImageButton Ibutton2 = (ImageButton) findViewById(R.id.button_2);
Ibutton2.setOnClickListener(this);

We now create the implemented method for our activity (onClick) and we use a switch statement to find which View fired the onclick event and preform an action accordingly.

@Override
public void onClick(View v) {
	switch(v.getId()){
	case R.id.button_1:
		// action to preform on button 1
		Toast.makeText(testActivity.this, "Button 1 pressed ", Toast.LENGTH_SHORT).show();
		break;
	case R.id.button_2:
		// action to preform on button 1
		Toast.makeText(testActivity.this, "Button 2 pressed ", Toast.LENGTH_SHORT).show();
		break;
	}
}

And it’s as simple as that!
Feel free to post comments or questions

I received several requests regarding how I created a context menu (the menu activated on a long press) using a gridview and how to call functions such as saving a sound file from this. So I have created a quick example to explain this:

Tutorial

To implement a context menu (long press menu) you first need to include the following imports:

import android.view.ContextMenu;
import android.view.View;
import android.view.ContextMenu.ContextMenuInfo;

We start a very simple project, with the layout having a single button named button_example:

Android context menu example

We then use registerForContextMenu in the onCreate of the activity to tell android that we want this view to create a menu when it is long pressed. This is not limited to buttons, this will work for other views too. You must register each view that you want to have associated with the context menu.

Button btn = (Button) findViewById(R.id.button_example);
registerForContextMenu(btn);

You then need to override the onCreateContextMenu method to create the menu:

    @Override
    public void onCreateContextMenu(ContextMenu menu, View v,ContextMenuInfo menuInfo) {
	super.onCreateContextMenu(menu, v, menuInfo);
		menu.setHeaderTitle("Context Menu");
		menu.add(0, v.getId(), 0, "Action 1");
		menu.add(0, v.getId(), 0, "Action 2");
	}

android context menu example

And override onContextItemSelected to preform the action when an option is selected from this menu:

    @Override
	public boolean onContextItemSelected(MenuItem item) {
       	if(item.getTitle()=="Action 1"){function1(item.getItemId());}
    	else if(item.getTitle()=="Action 2"){function2(item.getItemId());}
    	else {return false;}
	return true;
	}

function1 and function2 are just place-holders at the moment that toast a message when they are used. In the above example we are choosing between Action 1 and Action 2 which define which function will be run when an item is selected. We have passed the ID of the view through the context menu and into this function so we can tell what the user was pressing when the context menu was created.

calling a function after a context menu item was pressed

Examples

If you create a gridview and give each item a unique ID then you can use this method to preform actions based on each item. This is the method I use for my soundboard applications to save the sounds to the SD card as a notification or ringtone:

counterstrike 1.6 soundboard context menu

Unreal Tournament soundboard context menu

Source

Below is the source code:

package com.contextmenu.test;

import android.app.Activity;
import android.os.Bundle;
import android.view.ContextMenu;
import android.view.MenuItem;
import android.view.View;
import android.view.ContextMenu.ContextMenuInfo;
import android.widget.Button;
import android.widget.Toast;

public class test extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        Button btn = (Button) findViewById(R.id.button_example);
        registerForContextMenu(btn);
    }

    @Override
    public void onCreateContextMenu(ContextMenu menu, View v,ContextMenuInfo menuInfo) {
	super.onCreateContextMenu(menu, v, menuInfo);
		menu.setHeaderTitle("Context Menu");
		menu.add(0, v.getId(), 0, "Action 1");
		menu.add(0, v.getId(), 0, "Action 2");
	}

    @Override
	public boolean onContextItemSelected(MenuItem item) {
       	if(item.getTitle()=="Action 1"){function1(item.getItemId());}
    	else if(item.getTitle()=="Action 2"){function2(item.getItemId());}
    	else {return false;}
	return true;
	}

    public void function1(int id){
    	Toast.makeText(this, "function 1 called", Toast.LENGTH_SHORT).show();
    }
    public void function2(int id){
    	Toast.makeText(this, "function 2 called", Toast.LENGTH_SHORT).show();
    }
}