从一个片段开始一个活动

我有两个片段，两个片段上都有一个按钮。当我按下按钮时，我想开始一项新的活动。但是我不能让它工作。

我得到的错误是: 这里的错误: 类型不匹配: 无法从 mFragmentFavorite 转换为片段

我做错了什么？

适配器

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;
}
}

最喜爱的活动

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;
}
}

如果 FavoriteActivity 扩展了片段，那么错误就消失了，但是在 findViewById(R.id.mainFavorite);处我得到了一个错误，错误是

未为该类型定义 findViewById (int)方法 最喜爱的活动

编辑:

当我按下片段中的按钮开始活动时，应用程序崩溃了 这是我的木猫

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)
315421 次浏览
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最佳答案

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 {
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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.

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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;
}
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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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You may have to replace getActivity() with MainActivity.this for those that are having issues with this.

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Start new Activity From a Fragment:

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

Start new Activity From a Activity:

Intent intent = new Intent(this, TargetActivity.class);
startActivity(intent);
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with Kotlin I execute this code:

requireContext().startActivity<YourTargetActivity>()


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