Android 如何在课堂上访问资源？

Question

I am trying to get String app_name from resources but I keep getting a null object reference . How can I fix it?

package com.testandroid;

import android.app.Activity;
import android.content.Context;
import android.util.Log;
import java.util.HashMap;


public class Test extends Activity {
    public Test() {
        try {
            String hello = getString(R.string.app_name);

        } catch (Exception e) {
            Log.d("myLogs", e.getMessage());
        }
      }
}


<resources>
    <string name = "app_name">Name</string>
</resources>

Answer 1

string hello = getResources().getString(R.string.app_name);

Answer 2

Never, never override activity's constructor, this can lead to serious problems. If you need to initialise something at construction of activity, do it in onCreate, in constructor resources are NOT ready to use, so you cannot use them at this time.

Answer 3

public class Test extends Activity { 
@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.your_layout_here);
        String hello = getString(R.string.app_name);
        Log.d("Log", hello);

}

Also this should be placed into strings.xml in values folder

<resources>
    <string name = "app_name">Name</string>
</resources>

Answer 4

Ok, the easiest way is to use Context.

public class Test extends Activity {
    public Test(Context context) {
        try {
            String hello = context.getResources().getString(R.string.app_name)

        } catch (Exception e) {
            Log.d("myLogs", e.getMessage());
        }
      }
}