Android onClick method doesn't work on a custom view

Question

I\'ve started working on an app. I build the menu yesterday but the onClick method doesn\'t work! I created a class that extends View and called her MainMenuObject - that cl

Answer 1

Creating custom controls in Android can be tricky if you aren't comfortable with how the UI Framework operates. If you haven't already, I would recommend reading these:

http://developer.android.com/guide/topics/ui/declaring-layout.html

http://developer.android.com/guide/topics/ui/custom-components.html

http://developer.android.com/guide/topics/ui/layout-objects.html

Notice that when layouts are declared in XML the elements are nested. This creates a layout hierarchy that you must create your self when customizing a component using only Java code.

Most likely you are getting caught up in Android's touch hierarchy. Unlike some other popular mobile platforms, Android delivers touch events starting at the top of the View hierarchy and works its way down. The classes that traditionally occupy the higher levels of the hierarchy (Activity and Layouts) have logic in them to forward touches they don't themselves consume.

So, what I would recommend doing is changing your OpeningTimesView to extend a ViewGroup (the superclass of all Android layouts) or a specific layout (LinearLayout, RelativeLayout, etc.) and add your buttons as children. Right now, there does not seem to be a defined hierarchy (the buttons aren't really "contained" in the container, they're just members) which may be confusing the issue as to where events are really going.

1. The touches should more naturally flow down to the buttons, allowing your click events to trigger
2. You can take advantage of Android's layout mechanisms to draw your view instead of relying on drawing code to do all of that.

Pick a layout class to start with that will help you place your buttons in their FINAL locations. You can use the animation framework in Android or custom drawing code (like you have now) to animate them anyway you like up to that point. The location of a button and where that button is currently drawn are allowed to be very different if necessary, and that's how the current Animation Framework works in Android (prior to 3.0)...but that's a separate issue. You also have AbsoluteLayout, which allows you to place and replace objects anywhere you like...but be careful of how your app looks on all Android devices with this one (given the different screen sizes).

As to your second point about display info. The simplest method is probably just to use Context.getResources().getDisplayMetrics() wherever you need it. Activity inherits from Context, so they can call this method directly. Views always have a Context you can access with getContext(). Any other classes you can just pass the Context as a parameter in construction (this is a common pattern in Android, you'll see many objects require a Context, mainly to access Resources).

Here's a skeleton example to jump start things. This just lines the three up horizontally once as a final location:

Public class OpeningTimesView extends LinearLayout implements OnClickListener {
    private MainMenuObjectView searchButton;
    private MainMenuObjectView supportButton;
    private MainMenuObjectView aboutButton;
    private int screenWidth;
    private int screenHeight;

    public OpeningTimesView(Context context) {
        this(context, null);
    }

    //Thus constructor gets used if you ever instantiate your component from XML
    public OpeningTimesView(Context context, AttributeSet attrs) {
        super(context, attrs);

        /* This is a better way to obtain your screen info
        DisplayMetrics display = context.getResources().getDisplayMetrics();
        screenWidth = display.widthPixels;
        screenHeight = display.heightPixels;
        */
        //This way works also, without needing to customize the constructor
        WindowManager wm = (WindowManager)context.getSystemService(Context.WINDOW_SERVICE);
        Display dis = wm.getDefaultDisplay();
        screenWidth = dis.getWidth();
        screenHeight = dis.getHeight();

        searchButton = new MainMenuObjectView(context, 200, MovingMode.RIGHT, R.drawable.search, dis);
        supportButton = new MainMenuObjectView(context, 400, MovingMode.LEFT, R.drawable.support, dis);
        aboutButton = new MainMenuObjectView(context, 600, MovingMode.RIGHT, R.drawable.about, dis);

        //Even if they don't extend button, if MainMenuObjectView is always clickable
        // this should probably be brought into that class's constructor
        searchButton.setClickable(true);
        supportButton.setClickable(true);
        aboutButton.setClickable(true);

        searchButton.setOnClickListener(this);
        supportButton.setOnClickListener(this);
        aboutButton.setOnClickListener(this);

        //Add the buttons to the layout (the buttons are now children of the container)
        setOrientation(LinearLayout.HORIZONTAL);
        LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
        addView(searchButton, params);
        addView(supportButton, params);
        addView(aboutButton, params);       
    }

    @Override
    public void onClick(View view){
        Toast.makeText(getContext(), "Search button pressed", Toast.LENGTH_SHORT).show();
        if(view == searchButton){
            Toast.makeText(getContext(), "Search button pressed", Toast.LENGTH_SHORT).show();
        }
        else if(view == supportButton){
            Toast.makeText(getContext(), "Support button pressed", Toast.LENGTH_SHORT).show();
        }
        else Toast.makeText(getContext(), "About button pressed", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onDraw(Canvas canvas)
    {
        //Drawing the buttons
        // This may only be necessary until they are in place, then just call super.onDraw(canvas)
        this.searchButton.onDraw(canvas);
        this.aboutButton.onDraw(canvas);
        this.supportButton.onDraw(canvas);
    }    
}

You can customize this from there. Perhaps starting the buttons with visibility set to View.INVISIBLE until you animate them in with your drawing code or a custom Animation object, then making them visibile in their final resting place.

The key here, though, is the the layout is smart enough to know that when it receives a touch event it is supposed to forward it to the corresponding child. You can create a custom view without this, but you will have to intercept all touches on the container and do the math to determine which subview to manually forward the event to. If you truly can't make any layout manager work, this is your recourse.

Hope that Helps!

Answer 2

I do this so:

public class YourView extends LinearLayout implements OnClickListener {
    OnClickListener listener;

    //... constructors

    public void setOnClickListener(OnClickListener listener) {
        this.listener = listener;
    }

    @Override
    public void onClick(View v) {
        if (listener != null)
             listener.onClick(v);
    }
}

Answer 3

I just had the same Problem - I created a custom view and when I registered a new Listener for it in the activity by calling v.setOnClickListener(new OnClickListener() {...}); the listener just did not get called.

In my custom view I also overwrote the public boolean onTouchEvent(MotionEvent event) {...} method. The problem was that I did not call the method of the View class - super.onTouchEvent(event). That solved the problem. So if you are wondering why your listener does not get called you have probably forgotten to call the superclass'es onTouchEvent method

Here is a simple example:

private static class CustomView extends View implements View.OnClickListener {
    public CustomView(Context context) {
        super(context);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        super.onTouchEvent(event);   // this super call is important !!!
        // YOUR LOGIC HERE
        return true;
    }

    @Override
    public void onClick(View v) {
        // DO SOMETHING HERE
    }
}

Answer 4

just add callOnClick() to your onTouchEvent() method

public boolean onTouchEvent(MotionEvent event) {
        .....YOURCODE.....
        callOnClick();
        return boolean;
    }