Question

我试图用if和else来使用片段改变片段。当我试图运行程序时，我遇到了这个错误：

＆＃34;尝试写入字段＆＃39; int android.app.Fragment.mNextAnim＆＃39;在空对象引用＆＃34;

我搜索答案，我看到mybe the sulotion是导入Fragmet.support.v4.app.Fragment

所以试过了，我不能改变这个导入我应该怎么做或其他闷闷不乐？

import android.app.Fragment;
import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity implements  View.OnClickListener {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);


    if(isInSingleFrragment()){
        FragmentManager fm = getFragmentManager();
        Fragment fragmentB = fm.findFragmentById(R.id.FragmetB);
        FragmentTransaction ft=fm.beginTransaction();
        ft.hide(fragmentB);
        ft.commit();

        Button switchbutton = (Button)findViewById(R.id.switchbutton);
        switchbutton.setOnClickListener(this);
    }
}

private boolean isInSingleFrragment() {

    View layout = findViewById(R.id.singleLayout);

    if (layout != null) {
        return true;
    } else {
        return false;
    }
}
@Override
public void onClick(View v) {
    switch (v.getId()){
        case R.id.switchbutton:
            switchFragments();
            break;
    }

}

private void switchFragments() {

    FragmentManager fm = getFragmentManager();
    Fragment fragmentA = fm.findFragmentById(R.id.FragmetA);
    Fragment fragmentB = fm.findFragmentById(R.id.FragmetB);

    FragmentTransaction ft = fm.beginTransaction();

    if(fragmentA.isVisible()){
        ft.hide(fragmentA);
        ft.show(fragmentB);
    }else {
        ft.hide(fragmentB);
        ft.show(fragmentA);
    }
    ft.commit();
}
}

Answer 1

在隐藏fragmentB

之前添加一个null检查

if(isInSingleFrragment()){
    FragmentManager fm = getFragmentManager();
    Fragment fragmentB = fm.findFragmentById(R.id.FragmetB);
    FragmentTransaction ft = fm.beginTransaction();
    if (fragmentB != null) ft.hide(fragmentB);  // check != null
    ft.commit();
    ...
}

Answer 2

当你使用hide时，你必须有一个片段，使用.add（）。hide（）;错误告诉你那里没有片段

尝试写入字段＆＃39; int android.app.Fragment.mNextAnim＆＃39;在null对象引用上

2 个答案: