Creating class and passing content

Question

I made a method where all the font's get changed, but the problem is that I want to use the method once so I don't have to copy and paste it in every script.

Code example:

public void changeFont(){

    int[] id_et = {R.id.inputObjectName, R.id.inputObjectValue};
    int[] id_tv = {R.id.headerUserInfo, R.id.headerUserPW, R.id.headerUserGW};
    int[] id_btn = {R.id.privBtnIncome, R.id.privBtnExpense};

    Typeface font = Typeface.createFromAsset(getAssets(), "Sanford.TTF");

    for(int i = 0; i < id_et.length; i++){
        EditText textbox = (EditText) findViewById(id_et[i]);
        textbox.setTypeface(font);
    }

    for(int i = 0; i < id_tv.length; i++){
        TextView tv = (TextView) findViewById(id_tv[i]);
        tv.setTypeface(font);
    }

    for(int i = 0; i < id_btn.length; i++){
        Button btn = (Button) findViewById(id_btn[i]);
        btn.setTypeface(font);
    }

}

When I create a class and make an object to use the constructor to get the data, the program crashes.

This is how the class looks:

public class ChangeFont extends Activity{
    public ChangeFont(){

    int[] id_et = {R.id.inputObjectName, R.id.inputObjectValue};
    int[] id_tv = {R.id.headerUserInfo, R.id.headerUserPW, R.id.headerUserGW};
    int[] id_btn = {R.id.privBtnIncome, R.id.privBtnExpense};

    Typeface font = Typeface.createFromAsset(getAssets(), "Sanford.TTF");

    for(int i = 0; i < id_et.length; i++){
        EditText textbox = (EditText) findViewById(id_et[i]);
        textbox.setTypeface(font);
    }

    for(int i = 0; i < id_tv.length; i++){
        TextView tv = (TextView) findViewById(id_tv[i]);
        tv.setTypeface(font);
    }

    for(int i = 0; i < id_btn.length; i++){
        Button btn = (Button) findViewById(id_btn[i]);
        btn.setTypeface(font);
    }

    }

}

Error log:

12-12 17:23:49.746: E/AndroidRuntime(6159): FATAL EXCEPTION: main
12-12 17:23:49.746: E/AndroidRuntime(6159): java.lang.RuntimeException: Unable to start activity ComponentInfo{united.aristal.freewallet/united.aristal.freewallet.PrivateWallet}: java.lang.NullPointerException
12-12 17:23:49.746: E/AndroidRuntime(6159):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1955)
12-12 17:23:49.746: E/AndroidRuntime(6159):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1980)
12-12 17:23:49.746: E/AndroidRuntime(6159):     at android.app.ActivityThread.access$600(ActivityThread.java:122)
12-12 17:23:49.746: E/AndroidRuntime(6159):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1146)
12-12 17:23:49.746: E/AndroidRuntime(6159):     at android.os.Handler.dispatchMessage(Handler.java:99)
12-12 17:23:49.746: E/AndroidRuntime(6159):     at android.os.Looper.loop(Looper.java:137)
12-12 17:23:49.746: E/AndroidRuntime(6159):     at android.app.ActivityThread.main(ActivityThread.java:4340)
12-12 17:23:49.746: E/AndroidRuntime(6159):     at java.lang.reflect.Method.invokeNative(Native Method)
12-12 17:23:49.746: E/AndroidRuntime(6159):     at java.lang.reflect.Method.invoke(Method.java:511)
12-12 17:23:49.746: E/AndroidRuntime(6159):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
12-12 17:23:49.746: E/AndroidRuntime(6159):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
12-12 17:23:49.746: E/AndroidRuntime(6159):     at dalvik.system.NativeStart.main(Native Method)
12-12 17:23:49.746: E/AndroidRuntime(6159): Caused by: java.lang.NullPointerException
12-12 17:23:49.746: E/AndroidRuntime(6159):     at android.content.ContextWrapper.getAssets(ContextWrapper.java:75)
12-12 17:23:49.746: E/AndroidRuntime(6159):     at united.aristal.freewallet.ChangeFont.<init>(ChangeFont.java:16)
12-12 17:23:49.746: E/AndroidRuntime(6159):     at united.aristal.freewallet.PrivateWallet.onCreate(PrivateWallet.java:32)
12-12 17:23:49.746: E/AndroidRuntime(6159):     at android.app.Activity.performCreate(Activity.java:4465)
12-12 17:23:49.746: E/AndroidRuntime(6159):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
12-12 17:23:49.746: E/AndroidRuntime(6159):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1919)
12-12 17:23:49.746: E/AndroidRuntime(6159):     ... 11 more

So can anyone help me here?

Answer 1

getAssets is throwing NullPointerException because you created the ChangeFont instance instead of letting Android do it. If ChangeFont is just a utility class, it should not extend Activity.

Instead, initialize it with an instance of your actual activity, and let it call methods on that activity.

public class ChangeFont {

    public ChangeFont(final Activity activity) {
        this.activity = activity;

        Typeface font = Typeface.createFromAsset(activity.getAssets(), "Sanford.TTF");
    }

}