Why onDraw is not called after invalidate()?
AndroidAndroid Problem Overview
I have found many posts on stackoverflow but I still cannot solve my problem. Here is my code piece:
public class MyView extends RelativeLayout {
Button b1;
Button b2;
Context sContext;
public static int i = 0;
private int w = 400;
private int h = 400;
private int w2 = 100;
private int h2 = 100;
public MyView(Context context) {
super(context);
sContext = context;
init();
}
public MyView(Context context, AttributeSet attrs) {
super(context, attrs);
sContext = context;
init();
}
private void init() {
b1 = new Button(sContext);
addView(b1);
b1.setBackgroundColor(Color.YELLOW);
b1.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
if (w >= 600) {
MyView.this.setBackgroundColor(Color.GREEN);
//b1.setBackgroundColor(Color.RED);
} else {
MyView.this.setX(100);
}
MyView.this.invalidate();
w += 100;
w2 += 20;
}
});
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
//b1.setBackgroundColor(Color.RED);
Toast.makeText(sContext, ""+i, Toast.LENGTH_SHORT).show();
++i;
}
}
Would you please explain why onDraw is not called the first three times I press b1? Because I called invalidate everytime I press b1. Thank you very much!
Android Solutions
Solution 1 - Android
By default all ViewGroup sub-classes do not call their onDraw method, you should enable it by calling setWillNotDraw(false) link
Solution 2 - Android
Borrowing from the link @
https://stackoverflow.com/questions/13056331/android-custom-layout-ondraw-never-gets-called
Try the below it works
1.If you're extending a ViewGroup (in your case a RelativeLayout) you should override dispatchDraw() instead of onDraw().
Discussion on the topic @
https://groups.google.com/forum/?fromgroups=#!topic/android-developers/oLccWfszuUo
protected void dispatchDraw (Canvas canvas)
Called by draw to draw the child views. This may be overridden by derived classes to gain control just before its children are drawn (but after its own view has been drawn).
Parameters
canvas the canvas on which to draw the view
Example
public class Hello extends Activity {
private MyView myView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
super.onCreate(savedInstanceState);
Log.e("hello", "hello");
this.myView = new MyView(this);
setContentView(this.myView);
}
public class MyView extends RelativeLayout
{
private Paint myPaint = new Paint();
private int[] numbers;
public MyView(Context paramContext)
{
super(paramContext);
Log.e("MyView", "MyView");
setFocusable(true);
setBackgroundResource(R.drawable.ic_launcher);
}
@Override
protected void dispatchDraw(Canvas canvas){
super.dispatchDraw(canvas);
Log.i("...............","drawing");
}
}
}
2.If you Override onDraw in the constructor call setWillNotDraw(false) then it should work.
http://developer.android.com/reference/android/view/View.html#setWillNotDraw(boolean)
public MyView(Context context) {
super(context);
sContext = context;
init();
setWillNotDraw(false);
}
Solution 3 - Android
You need to call setWillNotDraw(false); in order for your onDraw method to be called:
private void init() {
setWillNotDraw(false);
...
}
Solution 4 - Android
I was having OnDraw not called in C# using 4.1 Jelly Bean API 16. I switched from compiling with API 16 SDK to compiling with 7.1 Nougat SDK. It solved the problem completely. I still have in manifest min sdk of API 16 and it runs fine in my Jelly Beam avd.
Solution 5 - Android
In my case onDraw was not called because I returned 0 as width or height of view.