Create Custom View and Add to XML

Question

I have created a custom View which draws a line:

public class DrawView extends View {
    Paint paint = new Paint();

    public DrawView(Context context) {
        super(context);
        paint.setColor(Color.BLACK);
    }

    @Override
    public void onDraw(Canvas canvas) {
        canvas.drawLine(0, 0, 100, 100, paint);
    }

}

I have a MainActivity class and activity_main layout where my layout contains an image and several buttons. I want to put the custom view that I created to my XML file(activity_main) where a line would be drawn on top of the image.

I tried adding it:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

//imageview and buttons here

<com.myapp.alphasickbro.myapplication2.DrawView
    android:id="@+id/paintView"
    android:layout_width="100dp"
    android:layout_height="100dp"
    />

</RelativeLayout>

Here is my MainActivity:

public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
}

}

But when I run it, the app unfortunately stops. Did I miss something? What lines of code should I add?

Any answer would be appreciated

EDIT:

04-18 15:24:47.517  26732-26732/com.myapp.alphasickbro.myapplication2 E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.myapp.alphasickbro.myapplication2, PID: 26732
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.myapp.alphasickbro.myapplication2/com.myapp.alphasickbro.myapplication2.MainActivity}: android.view.InflateException: Binary XML file line #6: Error inflating class com.myapp.alphasickbro.myapplication2.DrawView
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2318)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2396)
            at android.app.ActivityThread.access$800(ActivityThread.java:139)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1293)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:149)
            at android.app.ActivityThread.main(ActivityThread.java:5268)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:609)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: android.view.InflateException: Binary XML file line #6: Error inflating class com.myapp.alphasickbro.myapplication2.DrawView
            at android.view.LayoutInflater.createView(LayoutInflater.java:620)
            at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:696)
            at android.view.LayoutInflater.rInflate(LayoutInflater.java:755)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:492)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:397)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:353)
            at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:290)
            at android.app.Activity.setContentView(Activity.java:2002)
            at com.myapp.alphasickbro.myapplication2.MainActivity.onCreate(MainActivity.java:15)
            at android.app.Activity.performCreate(Activity.java:5411)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2270)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2396)
            at android.app.ActivityThread.access$800(ActivityThread.java:139)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1293)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:149)
            at android.app.ActivityThread.main(ActivityThread.java:5268)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:609)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.reflect.InvocationTargetException
            at java.lang.reflect.Constructor.constructNative(Native Method)
            at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
            at android.view.LayoutInflater.createView(LayoutInflater.java:594)
            at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:696)
            at android.view.LayoutInflater.rInflate(LayoutInflater.java:755)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:492)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:397)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:353)
            at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:290)
            at android.app.Activity.setContentView(Activity.java:2002)
            at com.myapp.alphasickbro.myapplication2.MainActivity.onCreate(MainActivity.java:15)
            at android.app.Activity.performCreate(Activity.java:5411)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2270)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2396)
            at android.app.ActivityThread.access$800(ActivityThread.java:139)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1293)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:149)
            at android.app.ActivityThread.main(ActivityThread.java:5268)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:609)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.myapp.alphasickbro.myapplication2.DrawView.<init>(DrawView.java:27)
            at java.lang.reflect.Constructor.constructNative(Native Method)
            at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
            at android.view.LayoutInflater.createView(LayoutInflater.java:594)
            at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:696)
            at android.view.LayoutInflater.rInflate(LayoutInflater.java:755)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:492)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:397)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:353)
            at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:290)
            at android.app.Activity.setContentView(Activity.java:2002)
            at com.myapp.alphasickbro.myapplication2.MainActivity.onCreate(MainActivity.java:15)
            at android.app.Activity.performCreate(Activity.java:5411)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2270)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2396)
            at android.app.ActivityThread.access$800(ActivityThread.java:139)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1293)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:149)
            at android.app.ActivityThread.main(ActivityThread.java:5268)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:609)
            at dalvik.system.NativeStart.main(Native Method)

You have created a paintView in XML, but you have not set the canvas to it. — Iqbal S
– Iqbal S, Commented Apr 18, 2015 at 6:40
@Iqbal How would I do that? Can you post it as an answer. Just a newbie here — yologaming
– yologaming, Commented Apr 18, 2015 at 6:44

Bojan Kseneman · Accepted Answer · 2015-04-18 07:44:15Z

1

I think you need to add the missing constructors. Clean your project.

public class DrawView extends View {

    Paint paint;

    public DrawView(Context context) {
        super(context);
        init();
    }

    public DrawView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();

    }

    public DrawView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init();
    }

    private void init() {
        paint = new Paint();
        paint.setColor(Color.BLACK);
    }
}

edited Apr 18, 2015 at 7:44

answered Apr 18, 2015 at 7:00

Bojan Kseneman

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3 Comments

yologaming Over a year ago

Missing constructors? I already created a constructor for DrawView, what else should I add.

Bojan Kseneman Over a year ago

When you use your view from xml, the constructor with attributeset is used, since you had none.. The problem. See edit.

yologaming Over a year ago

I tried it but it still stopped when I run it. No errors but when ran, a lot of errors are shown in logcat. I updated my post, pls see logcat if necessary.

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