Question

Hello I want to make an application which uses Multi-touch support.

for multitouch i am using this code

Now in that you can see that there is org.metalev.multitouch.photosortr.PhotoSortrActivity Activity
in that the code is like below

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    this.setTitle(R.string.instructions);
    photoSorter = new PhotoSortrView(this);
    setContentView(photoSorter);
}

it will work fine

but instead of this if i want to add this view in my view i write above code like below…

i have make one XML file named activity_main.xml

<org.metalev.multitouch.photosortr.PhotoSortrView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

</org.metalev.multitouch.photosortr.PhotoSortrView>

and in onCreate method i have change like below

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    this.setTitle(R.string.instructions);
    photoSorter = new PhotoSortrView(this);
    setContentView(R.layout.activity_main);
}

if i do like this way i will get an error below is logcat

10-30 12:15:29.319: E/AndroidRuntime(6652): java.lang.NullPointerException
10-30 12:15:29.319: E/AndroidRuntime(6652):     at org.metalev.multitouch.photosortr.PhotoSortrView$Img.draw(PhotoSortrView.java:274)
10-30 12:15:29.319: E/AndroidRuntime(6652):     at org.metalev.multitouch.photosortr.PhotoSortrView.onDraw(PhotoSortrView.java:86)
10-30 12:15:29.319: E/AndroidRuntime(6652):     at android.view.View.draw(View.java:6914)
10-30 12:15:29.319: E/AndroidRuntime(6652):     at android.view.ViewGroup.drawChild(ViewGroup.java:1646)
10-30 12:15:29.319: E/AndroidRuntime(6652):     at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373)
10-30 12:15:29.319: E/AndroidRuntime(6652):     at android.view.View.draw(View.java:6917)
10-30 12:15:29.319: E/AndroidRuntime(6652):     at android.widget.FrameLayout.draw(FrameLayout.java:357)
10-30 12:15:29.319: E/AndroidRuntime(6652):     at android.view.ViewGroup.drawChild(ViewGroup.java:1646)
10-30 12:15:29.319: E/AndroidRuntime(6652):     at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373)
10-30 12:15:29.319: E/AndroidRuntime(6652):     at android.view.ViewGroup.drawChild(ViewGroup.java:1644)

in PhotoSortrView.java file the code is like below where i m getting this error

public void draw(Canvas canvas) {
    canvas.save();
    float dx = (maxX + minX) / 2;
    float dy = (maxY + minY) / 2;
    ---->drawable.setBounds((int) minX, (int) minY, (int) maxX, (int) maxY); // HERE getting drawable == NULL
    canvas.translate(dx, dy);
    canvas.rotate(angle * 180.0f / (float) Math.PI);
    canvas.translate(-dx, -dy);
    drawable.draw(canvas);
    canvas.restore();
}

Answer 1

Only cause might be that drawable used in draw() of Img class is null, since canvas is passed by system, and rest variables in method are primitives. This variable is initialized in load() of Img class , which in turn is called from loadImages() of PhotoSortrView class.

Now, I guess you are calling loadImages() of photoSorter variable from Activity’s onResume() . But there is another PhotoSortrView instance created from inflating the layout. Make sure you call loadImages() of that instance also.