《Android开发权威指南》(第三版)第十一章挑战练习

直接上代码：

//Activity代码
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.Button;

import java.util.List;
import java.util.UUID;

public class SecretPagerActivity extends AppCompatActivity {

private ViewPager mViewPager;
private List<Secret> mSecrets;
private Button mToFirst;
private Button mToLast;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_secret_pager);
mViewPager = findViewById(R.id.activity_secret_pager_view_pager);
mToFirst=findViewById(R.id.bt_tofirst);
mToLast=findViewById(R.id.bt_tolast);

mToLast.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
mViewPager.setCurrentItem(99);
}
});
mToFirst.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
mViewPager.setCurrentItem(0);
}
});
mSecrets = SecretLab.get(this).getSecrets();
UUID uuid = (UUID) getIntent().getSerializableExtra("uuid");

FragmentManager fm = getSupportFragmentManager();
mViewPager.setAdapter(new FragmentStatePagerAdapter(fm) {
@Override
public Fragment getItem(int position) {
Secret secret = mSecrets.get(position);
Log.e("CurrentItem==>",mViewPager.getCurrentItem()+"");
if(mViewPager.getCurrentItem()==0){
mToFirst.setEnabled(false);
}
else{
mToFirst.setEnabled(true);
if(mViewPager.getCurrentItem()==99){
mToLast.setEnabled(false);
}
else{
mToLast.setEnabled(true);
}
}
return SecretFragment.newInstance(secret.getNum());
}

@Override
public int getCount() {
return mSecrets.size();
}
});

int cnt = mSecrets.size();
for (int i = 0; i < cnt; i++) {
if (mSecrets.get(i).getNum().equals(uuid)) {
mViewPager.setCurrentItem(i);
break;
}
}
}

public static Intent newIntent(Context context, UUID secret_id) {
Intent intent = new Intent(context, SecretPagerActivity.class);
intent.putExtra("uuid", secret_id);
return intent;
}
}

<!--布局文件代码-->
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_height="match_parent"
android:layout_width="match_parent"
android:orientation="vertical">

<FrameLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/bt_tofirst"
android:text="JUMP TO THE FIRST"/>

<Button
android:id="@+id/bt_tolast"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="right|bottom"
android:text="JUMP TO LAST" />
</FrameLayout>

<LinearLayout
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:orientation="vertical">

<android.support.v4.view.ViewPager
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/activity_secret_pager_view_pager">
</android.support.v4.view.ViewPager>

</LinearLayout>

</LinearLayout>

注：1、在布局文件中，如果先定义ViewPager，再定义按钮的话，按钮会加载不出来。所以我把两个按钮定义在了顶部。如果有小伙伴知道怎么在ViewPager底下定义按钮的话，欢迎指点。2、在左右滑动的时候，FragmentStatePaperAdapter对于刚刚划走的Fragment好像是不会彻底销毁的，所以，从Item0->Item1->Item0时，JUMP　TO　THE　First按钮并不会失效，参考链接：http://blog.csdn.net/fangkailong/article/details/38298893