Gorthez Gorthez - 2 months ago 21
Android Question

Change code to android annotations

I'm trying to change my code to android annotations. My app starts but when I tap button it crash and get error:


FATAL EXCEPTION: main
Process: com.example.albertpula.apka3, PID: 2523
java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.widget.ProgressBar.setVisibility(int)' on a null object
reference
at
com.example.albertpula.apka3.MainActivity$ReadPic.onPreExecute(MainActivity.java:83)
at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:604)
at android.os.AsyncTask.execute(AsyncTask.java:551)
at
com.example.albertpula.apka3.MainActivity.click(MainActivity.java:54)
at
com.example.albertpula.apka3.MainActivity_$1.onClick(MainActivity_.java:72)
at android.view.View.performClick(View.java:5198)
at android.view.View$PerformClick.run(View.java:21147)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)


here is code:

@EActivity(R.layout.activity_main)
public class MainActivity extends Activity {

String adres ="http://www.heavens-above.com/orbitdisplay.aspx?icon=iss&width=300&height=300&satid=25544";
Bitmap bmp;
ProgressBar progressBar;
Button button1;
ImageView image;
TextView text;

@Override
public void onCreate(Bundle savedInstanceState)
{
image = (ImageView)findViewById(R.id.imageView);
button1 = (Button)findViewById(R.id.button1);
progressBar = (ProgressBar)findViewById(R.id.progressBar1);
text = (TextView)findViewById(R.id.textView1);

super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}

@Click(R.id.button1)
void click(View view){
ReadPic rp = new ReadPic();
rp.execute();
}

class ReadPic extends AsyncTask<Void, Void, Void>
{
boolean sukces = true;

@Override
protected Void doInBackground(Void... arg0){
URL u;
InputStream is;
try{

u = new URL( adres);
is = u.openStream();
Bitmap temp = BitmapFactory.decodeStream(is);
bmp=temp.copy(Bitmap.Config.ARGB_8888, true);
}
catch( Exception e){
sukces = false;

}
return null;
}

protected void onPreExecute(){
progressBar.setVisibility(ProgressBar.VISIBLE);
button1.setEnabled(false);
super.onPreExecute();
}

protected void onPostExecute(Void result){
if(sukces){
Canvas c = new Canvas(bmp);
Paint p = new Paint();
int width = bmp.getWidth(), height = bmp.getHeight();
p.setColor(Color.WHITE);
p.setStyle(Paint.Style.STROKE);
c.drawRect(0,0,width-1,height-1,p);

image.setImageBitmap(bmp);
text.setText("Downloading finished, img " +width+ "x" + height);
}
else{
text.setText("Error when downloading");
}
button1.setEnabled(true);
progressBar.setVisibility(ProgressBar.INVISIBLE);

super.onPostExecute(result);
}
}
}

Answer
  1. Use ViewBinding for binding your xml views like this :

    @ViewById(R.id.button1)Button button1;
    
    @ViewById(R.id.imageView)ImageView image;
    
    @ViewById(R.id.textView1)TextView text;
    

Remove the code from your onCreate().

  1. Don't add :

    super.onCreate(savedInstanceState);
    
    setContentView(R.layout.activity_main);
    
  2. For the error: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ProgressBar.setVisibility(int)' on a null object reference at

Option :1 Check if it is null.

protected void onPreExecute(){
    if(progressBar != null)
        progressBar.setVisibility(ProgressBar.VISIBLE);

    button1.setEnabled(false);
    super.onPreExecute();
}

AND,

button1.setEnabled(true); 

if(progressBar != null)
progressBar.setVisibility(ProgressBar.INVISIBLE);

super.onPostExecute(result);

Option :2 - Initialize the ProgressDialog

 class ReadPic extends AsyncTask<Void, Void, Void> {
     ProgressBar progressBar;
     boolean sukces = true;

     public ReadPic(){
         progressBar = new ProgressBar();//Set the Theme, context & call constructor as per your choice.
     }

     //YOUR CODE GOES BELOW// 
  }//ReadPic class closes here....

Edit 1: Gorthez, instantiate your Progress bar like this:

progressBar = (ProgressBar) findViewById(R.id.progress_bar);

Also Add Progress Bar in your xml:

<LinearLayout
      android:orientation="horizontal"
      ... >
        <ProgressBar
          android:id="@+id/progress_bar"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          style="@android:style/Widget.ProgressBar.Small"
          android:layout_marginRight="5dp" />
      <TextView
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:text="@string/loading" />  </LinearLayout>

Edit1 Reference https://developer.android.com/reference/android/widget/ProgressBar.html

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