Question

I have to use a canvas class to add frame and multiple images on it. but my problem is that I have to use canvas view in my activity class. I want to use this canvas view as a widget so I can use it in my XML.

I tried this by using this code :

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.util.AttributeSet;
import android.view.View;

public class TwoDee extends View {
    private int mWidth;
    private int mHeight;


    public TwoDee(Context context) {
        super(context);
    }

    public TwoDee(Context context, AttributeSet attribs) {
        super(context, attribs);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        Paint paint = new Paint(); 
        paint.setColor(Color.GRAY); 
        paint.setStyle(Style.FILL); 
        canvas.drawPaint(paint);

        paint.setColor(Color.BLUE);
        canvas.drawLine(0, 0, mWidth, mHeight, paint);
        canvas.drawLine(mWidth, 0, 0, mHeight, paint);

        paint.setColor(Color.RED);
        canvas.drawText("0 kal", 50, 85, paint);
        canvas.save();
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        mWidth = View.MeasureSpec.getSize(widthMeasureSpec);
        mHeight = View.MeasureSpec.getSize(heightMeasureSpec);
        setMeasuredDimension(mWidth, mHeight);
    }

    public void setImage(Drawable myImg) {
        newImg = myImg;
        invalidate();
    }
}

and used it in my xml class like this :

<?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"
    >
        <TextView  
            android:layout_width="fill_parent" 
            android:layout_height="wrap_content" 
            android:text="@string/hello"
        />
        <com.yourapphere.TwoDee
            android:id="@+id/twoDee1"
            android:layout_width="150dp"
            android:layout_height="100dp"
        />
</LinearLayout>

and I am accessing it in my activity class like this :

TwoDee myCanvas;
myCanvas = (TwoDee)findViewById(R.id.twoDee1);
myCanvas.setImage(drawable);

my problem is that when I try to call setImage() function from my activity class it shows null pointer exception. What should I do to add image in canvas view using my Activity class.
I dont want to use setContentView because this will make only Canvas View to show in my activity.

LogCat Output :

FATAL EXCEPTION: main
java.lang.NullPointerException
at iTagz.android.Dialog_ImagePreview$1.onClick(Dialog_ImagePreview.java:84)
at android.view.View.performClick(View.java:2485)
at android.view.View$PerformClick.run(View.java:9081)
at android.os.Handler.handleCallback(Handler.java:587)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:130)
at android.app.ActivityThread.main(ActivityThread.java:3770)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:507)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:880)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:638)
at dalvik.system.NativeStart.main(Native Method)

Dialog_ImagePreview is my activity from where I’m calling SetImage method.

Answer 1

I was calling my view from other activity and that’s why I was getting NullPointerException. But now i’m calling it from same activity and its working fine.