android - 如何根据 firebase 值检查字符串

Question

所以我的应用程序中有搜索功能，它可以很好地搜索数据库中的内容。但是当该项目不在我的数据库中时，我会收到一个 fatal error 。

搜索功能有一个 edittext 和一个按钮，当按钮被触发时，它会检查数据库以获取对 edittext 的引用。

这是我的代码。

    public void searchfunction() {
    mArraylist.clear();
    final ChildEventListener msearchevent = new ChildEventListener() {

        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {

            String msearchname = dataSnapshot.child("name").getValue(String.class);

            final String url = dataSnapshot.child("url").getValue(String.class);

            if (msearchname.toLowerCase().contains(searchapps.toLowerCase())) {
                marrayAdapter2 = new ArrayAdapter(MainActivity.this, android.R.layout.simple_list_item_1, mArraylist);
                mlv.setAdapter(marrayAdapter2);

                mArraylist.add(msearchname);
                mArraylist2.add(url);
                marrayAdapter2.notifyDataSetChanged();
                mlv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                    @Override
                    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                        DownloadFileFromURL dl = new DownloadFileFromURL(mContext, apkNames, mCurrentPhotoPath);
                        dl.execute(mArraylist2.get(position));
                    }
                });

            }else {
                Toast.makeText(MainActivity.this, "No results found!",Toast.LENGTH_SHORT).show();
            }

        }


        @Override
        public void onChildChanged(DataSnapshot dataSnapshot, String s) {
            marrayAdapter2.notifyDataSetChanged();

        }

        @Override
        public void onChildRemoved(DataSnapshot dataSnapshot) {
            marrayAdapter2.notifyDataSetChanged();
        }

        @Override
        public void onChildMoved(DataSnapshot dataSnapshot, String s) {
            marrayAdapter2.notifyDataSetChanged();
        }

        @Override
        public void onCancelled(FirebaseError firebaseError) {
            marrayAdapter2.notifyDataSetChanged();
        }
    };
    mListRef.child("Filmapps").addChildEventListener(msearchevent);

我的按钮点击是在 GetView 函数中处理的这是我点击按钮的代码

 mgoButton.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        searchapps = msearch.getText().toString().trim();
        searchfunction();
        InputMethodManager inputManager = (InputMethodManager)
                getSystemService(Context.INPUT_METHOD_SERVICE);

        inputManager.hideSoftInputFromWindow(getCurrentFocus().getWindowToken(),
                InputMethodManager.HIDE_NOT_ALWAYS);
    }
});

06-27 17:51:16.708 2938-2938/com.example.harrops.h20droidapp2 E/UncaughtException: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.String.toLowerCase()' on a null object reference
                                                                                   at com.example.harrops.h20droidapp2.actvities.MainActivity$3.onChildAdded(MainActivity.java:287)
                                                                                   at com.firebase.client.core.ChildEventRegistration.fireEvent(ChildEventRegistration.java:48)
                                                                                   at com.firebase.client.core.view.DataEvent.fire(DataEvent.java:45)
                                                                                   at com.firebase.client.core.view.EventRaiser$1.run(EventRaiser.java:38)
                                                                                   at android.os.Handler.handleCallback(Handler.java:751)
                                                                                   at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                   at android.os.Looper.loop(Looper.java:154)
                                                                                   at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                                                   at java.lang.reflect.Method.invoke(Native Method)
                                                                                   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                                                   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

06-27 17:51:16.712 2938-3140/com.example.harrops.h20droidapp2 D/FA:记录事件(FE):_ae，Bundle[{_o=crash，_sc=MainActivity，_si=7357998494779803214，时间戳=1498585876708，致命=1}]

Answer 1

getValue文档

An instance of the class passed in, populated with the data from this snapshot, or null if there is no data at this location.

所以添加一个无效检查

    if (msearchname!=null && url!=null && msearchname.toLowerCase().contains(searchapps.toLowerCase())) {

注意:&&是一个短路运算符，表示在表达式值为假的情况下不会执行if。