java - 加载数据并插入不显示的 RecyclerView

Question

我一直在关注 this guide用于 RecyclerView 并尝试将其用于我的特定用例，但在应用程序运行时 RecyclerView 为空。

我是 Java 和 Android 开发的新手，所以我只是进行测试以尝试掌握一些东西。在这种特殊情况下，我只是试图列出已安装的软件包，其中软件包名称以特定字符串开头，例如“com.google”应该匹配“com.google.camera”。

我的主要 Activity 如下所示:

public class MainActivity extends AppCompatActivity {

    ArrayList<PackageInfo> packages = new ArrayList<PackageInfo>();
    PackageManager pm;

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

        RecyclerView lstPackages = (RecyclerView) findViewById(R.id.lstInstalledPackages);

        pm = getPackageManager();
        List<PackageInfo> allPackages = pm.getInstalledPackages(PackageManager.GET_META_DATA);
        for(PackageInfo pkg : allPackages) {
            if(pkg.packageName.startsWith("com.google")){
                packages.add(pkg);
                Log.d("PKG", "Package found: " + pkg.packageName);
            }
        }

        PackageItemAdapter adapter = new PackageItemAdapter(packages);
        lstPackages.setAdapter(adapter);
        lstPackages.setLayoutManager(new LinearLayoutManager(this));
        adapter.notifyDataSetChanged();
    }
}

包裹元素:

public class PackageItem {
    private PackageInfo mPackageInfo;

    public PackageItem(PackageInfo packageInfo) {
        mPackageInfo = packageInfo;
    }

    public String getName() {
        return mPackageInfo.applicationInfo.name;
    }

    public String getPackageId() {
        return mPackageInfo.packageName;
    }

    public String getVersion() {
        return mPackageInfo.versionName;
    }
}

PackageItemAdapter:

public class PackageItemAdapter extends RecyclerView.Adapter<PackageItemAdapter.ViewHolder> {
    public class ViewHolder extends RecyclerView.ViewHolder {
        public TextView packageName;

        public ViewHolder(View viewItem) {
            super(viewItem);

            packageName = (TextView)viewItem.findViewById(R.id.txtPackageName);
        }
    }

    private List<PackageItem> mPackages;

    public PackageItemAdapter(List<PackageInfo> packages) {
        ArrayList<PackageItem> pis = new ArrayList<PackageItem>();
        for(PackageInfo pkg : packages) {
            pis.add(new PackageItem(pkg));
        }
        mPackages = pis;
    }

    @Override
    public PackageItemAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        Context context = parent.getContext();
        LayoutInflater inflater = LayoutInflater.from(context);

        View packageView = inflater.inflate(R.layout.packageitem, parent, false);

        ViewHolder viewHolder = new ViewHolder(packageView);
        return viewHolder;
    }

    @Override
    public void onBindViewHolder(PackageItemAdapter.ViewHolder viewHolder, int position) {
        PackageItem packageItem = mPackages.get(position);

        TextView tv = viewHolder.packageName;
        tv.setText(packageItem.getName());
    }

    @Override
    public int getItemCount() {
        return mPackages.size();
    }
}

packageitem.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal">

    <TextView
        android:id="@+id/txtPackageName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1" />
</LinearLayout>

您能看出我遗漏了什么吗，或者是否有一些怪癖或我必须考虑的事情才能使它正常工作，或者我完全不在乎？

Answer 1

我之前遇到过这个问题。您需要将 Layout Manager 设置为您的 recyclerView，因为没有它，您的 Recycler 就没有合适的布局，并且不知道如何在其中放置您的项目 View 。所以在你找到你的回收者 View 之后:

RecyclerView lstPackages = (RecyclerView) findViewById(R.id.lstInstalledPackages);

添加设置布局的行，如

lstPackages.setLayoutManager(new LinearLayoutManager(this));