Start an activity from a fragment

问题:

I have 2 fragments with on both fragments a button. When I press the button I'd like to start a new Activity. But I can't get it to work.

The error I'm getting: ERROR here: Type mismatch: cannot convert from mFragmentFavorite to Fragment

What am I doing wrong?

MyFragmentPagerAdapter

import android.support.v4.app.Fragment; import android.support.v4.app.FragmentManager; import android.support.v4.app.FragmentPagerAdapter;  public class MyFragmentPagerAdapter extends FragmentPagerAdapter{      final int PAGE_COUNT = 3;      /** Constructor of the class */     public MyFragmentPagerAdapter(FragmentManager fm) {         super(fm);     }      /** This method will be invoked when a page is requested to create */     @Override     public Fragment getItem(int arg0) {          switch(arg0){          case 0:             return new FavoriteActivity();                     //ERROR: Type mismatch: cannot convert from FavoriteActivity to Fragment           case 1:             return new SettingsActivity();           default:             return null;          }            }      /** Returns the number of pages */     @Override     public int getCount() {         return PAGE_COUNT;     } } 

FavoriteActivity

import android.app.Activity; import android.content.Intent; import android.os.Bundle; import android.view.LayoutInflater; import android.view.View; import android.view.View.OnClickListener; import android.view.ViewGroup; import android.widget.Button;  public class FavoriteActivity extends Activity{      public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {         View v = inflater.inflate(R.layout.main_favorite, container, false);           OnClickListener listnr=new OnClickListener() {             @Override             public void onClick(View v) {                   Intent i= new Intent("aFavorite");                   startActivity(i);             }         };            Button btn =(Button) v.findViewById(R.id.mainFavorite);           btn.setOnClickListener(listnr);            return v;     } } 

If FavoriteActivity extends fragments, the error is gone but then I get an error at findViewById(R.id.mainFavorite); and the error is

The method findViewById(int) is undefined for the type FavoriteActivity

EDIT:

When I press the button in the fragment to start the activity then the app crashes this is my logcat

03-18 16:01:23.985: E/AndroidRuntime(1985): FATAL EXCEPTION: main 03-18 16:01:23.985: E/AndroidRuntime(1985): android.content.ActivityNotFoundException: No Activity found to handle Intent { act=FavoriteActivityList } 03-18 16:01:23.985: E/AndroidRuntime(1985):     at android.app.Instrumentation.checkStartActivityResult(Instrumentation.java:1569) 03-18 16:01:23.985: E/AndroidRuntime(1985):     at android.app.Instrumentation.execStartActivity(Instrumentation.java:1420) 03-18 16:01:23.985: E/AndroidRuntime(1985):     at android.app.Activity.startActivityForResult(Activity.java:3446) 03-18 16:01:23.985: E/AndroidRuntime(1985):     at android.app.Activity.startActivityForResult(Activity.java:3407) 03-18 16:01:23.985: E/AndroidRuntime(1985):     at android.support.v4.app.FragmentActivity.startActivityFromFragment(FragmentActivity.java:826) 03-18 16:01:23.985: E/AndroidRuntime(1985):     at android.support.v4.app.Fragment.startActivity(Fragment.java:838) 03-18 16:01:23.985: E/AndroidRuntime(1985):     at com.example.spui.FavoriteActivity$1.onClick(FavoriteActivity.java:24) 03-18 16:01:23.985: E/AndroidRuntime(1985):     at android.view.View.performClick(View.java:4211) 03-18 16:01:23.985: E/AndroidRuntime(1985):     at android.view.View$PerformClick.run(View.java:17267) 03-18 16:01:23.985: E/AndroidRuntime(1985):     at android.os.Handler.handleCallback(Handler.java:615) 03-18 16:01:23.985: E/AndroidRuntime(1985):     at android.os.Handler.dispatchMessage(Handler.java:92) 03-18 16:01:23.985: E/AndroidRuntime(1985):     at android.os.Looper.loop(Looper.java:137) 03-18 16:01:23.985: E/AndroidRuntime(1985):     at android.app.ActivityThread.main(ActivityThread.java:4898) 03-18 16:01:23.985: E/AndroidRuntime(1985):     at java.lang.reflect.Method.invokeNative(Native Method) 03-18 16:01:23.985: E/AndroidRuntime(1985):     at java.lang.reflect.Method.invoke(Method.java:511) 03-18 16:01:23.985: E/AndroidRuntime(1985):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1006) 03-18 16:01:23.985: E/AndroidRuntime(1985):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:773) 03-18 16:01:23.985: E/AndroidRuntime(1985):     at dalvik.system.NativeStart.main(Native Method) 

回答1:

mFragmentFavorite in your code is a FragmentActivity which is not the same thing as a Fragment. That's why you're getting the type mismatch. Also, you should never call new on an Activity as that is not the proper way to start one.

If you want to start a new instance of mFragmentFavorite, you can do so via an Intent.

From a Fragment:

Intent intent = new Intent(getActivity(), mFragmentFavorite.class); startActivity(intent); 

From an Activity

Intent intent = new Intent(this, mFragmentFavorite.class); startActivity(intent); 

If you want to start aFavorite instead of mFragmentFavorite then you only need to change out their names in the created Intent.

Also, I recommend changing your class names to be more accurate. Calling something mFragmentFavorite is improper in that it's not a Fragment at all. Also, class declarations in Java typically start with a capital letter. You'd do well to name your class something like FavoriteActivity to be more accurate and conform to the language conventions. You will also need to rename the file to FavoriteActivity.java if you choose to do this since Java requires class names match the file name.

UPDATE

Also, it looks like you actually meant formFragmentFavorite to be a Fragment instead of a FragmentActivity based on your use of onCreateView. If you want mFragmentFavorite to be a Fragment then change the following line of code:

public class mFragmentFavorite extends FragmentActivity{ 

Make this instead read:

public class mFragmentFavorite extends Fragment { 

回答2:

You should use getActivity() to launch activities from fragments

Intent intent = new Intent(getActivity(), mFragmentFavorite.class); startActivity(intent); 

Also, you should be naming classes with caps: MFragmentActivity instead of mFragmentActivity.

回答3:

I use this in my fragment.

Button btn1 = (Button) thisLayout             .findViewById(R.id.btnDb1);      btn1.setOnClickListener(new OnClickListener() {          @Override         public void onClick(View v) {             // TODO Auto-generated method stub             Intent intent = new Intent(getActivity(), otherActivity.class);             ((MainActivity) getActivity()).startActivity(intent);          }     });      return thisLayout; } 

回答4:

If you are using getActivity() then you have to make sure that the calling activity is added already. If activity has not been added in such case so you may get null when you call getActivity()

in such cases getContext() is safe

then the code for starting the activity will be slightly changed like,

Intent intent = new Intent(getContext(), mFragmentFavorite.class); startActivity(intent); 

Activity, Service and Application extends ContextWrapper class so you can use this or getContext() or getApplicationContext() in the place of first argument.

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