Question

如何处理显示ListView的空视图的问题，因为当我从firebase数据库读取数据并将其显示在ListView中时，我不知道必须放入哪些数据。我使用CustomListAdapter更改ListView的字体颜色和背景颜色

注意：我正在从firebase数据库中读取数据并将其显示在ListView中，任何解决方案

CustomListAdapter.java

   public class CustomListAdapter extends BaseAdapter {

private static final int HERO_COUNT = 12;
private Context context;
private List<String> items;

public CustomListAdapter(Context context) {
    this.context = context;
    items = new ArrayList<>();
}

@Override
public int getCount() {
    return HERO_COUNT;
}

@Override
public String getItem(int position) {
    if (position >= 0 && position < items.size()) {
        return items.get(position);
    }
    return "";
}

@Override
public long getItemId(int position) {
    return 0;
}

@Override
public View getView(int position, View v, ViewGroup parent) {
    View mView = v;
    if (mView == null) {
        LayoutInflater vi = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        mView = vi.inflate(R.layout.custom_list, null, false);

        TextView text = (TextView) mView.findViewById(R.id.textView);
        //textView.setTextColor(Color.BLUE);
        text.setText(getItem(position));
        if (items.isEmpty()) {
            // Set holder color
        } else {
            text.setTextColor(Color.WHITE);
            int color = Color.argb(200, 255, 64, 64);
            text.setBackgroundColor(color);
        }


    }

    return mView;
}

public void updateList(List<String> updatedItems) {
    items.clear();
    items.addAll(updatedItems);
    notifyDataSetChanged();
}
}

ViewDatabase.java

public class ViewDatabase extends AppCompatActivity {
private static final String TAG = "ViewDatabase";

//add Firebase Database stuff
private FirebaseDatabase mFirebaseDatabase;
private FirebaseAuth mAuth;
private FirebaseAuth.AuthStateListener mAuthListener;
private DatabaseReference myRef;
private String userID;

private ListView mListView;


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

    mListView = (ListView) findViewById(R.id.listview);
    CustomListAdapter adapter = new CustomListAdapter(this);
    mListView.setAdapter(adapter);


    //declare the database reference object. This is what we use to access the database.
    //NOTE: Unless you are signed in, this will not be useable.
    mAuth = FirebaseAuth.getInstance();
    mFirebaseDatabase = FirebaseDatabase.getInstance();
    myRef = mFirebaseDatabase.getReference();
    FirebaseUser user = mAuth.getCurrentUser();
    // userID = user.getUid();
    userID = "";

    mAuthListener = new FirebaseAuth.AuthStateListener() {
        @Override
        public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
            FirebaseUser user = firebaseAuth.getCurrentUser();
            if (user != null) {
                // User is signed in
                Log.d(TAG, "onAuthStateChanged:signed_in:" + user.getUid());
                toastMessage("Successfully signed in.");
            } else {
                // User is signed out
                Log.d(TAG, "onAuthStateChanged:signed_out");
                toastMessage("Successfully signed out.");
            }
            // ...
        }
    };

    myRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            // This method is called once with the initial value and again
            // whenever data at this location is updated.
            showData(dataSnapshot);
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

}


private void showData(DataSnapshot dataSnapshot) {
    for (DataSnapshot ds : dataSnapshot.getChildren()) {
        DailyInfo uInfo = new DailyInfo();
        uInfo.setHero1(ds.child(userID).getValue(DailyInfo.class).getHero1()); //set the name1
        uInfo.setHero2(ds.child(userID).getValue(DailyInfo.class).getHero2()); //set the name2
        uInfo.setHero3(ds.child(userID).getValue(DailyInfo.class).getHero3()); //set the name3
        uInfo.setHero4(ds.child(userID).getValue(DailyInfo.class).getHero4()); //set the name4
        uInfo.setHero5(ds.child(userID).getValue(DailyInfo.class).getHero5()); //set the name5
        uInfo.setHero6(ds.child(userID).getValue(DailyInfo.class).getHero6()); //set the name6
        uInfo.setHero7(ds.child(userID).getValue(DailyInfo.class).getHero7()); //set the name7
        uInfo.setHero8(ds.child(userID).getValue(DailyInfo.class).getHero8()); //set the name8
        uInfo.setHero9(ds.child(userID).getValue(DailyInfo.class).getHero9()); //set the name9
        uInfo.setHero10(ds.child(userID).getValue(DailyInfo.class).getHero10()); //set the name10
        uInfo.setHero11(ds.child(userID).getValue(DailyInfo.class).getHero11()); //set the name11
        uInfo.setHero12(ds.child(userID).getValue(DailyInfo.class).getHero12()); //set the name12


        //display all the information
        Log.d(TAG, "showData: Hero1: " + uInfo.getHero1());
        Log.d(TAG, "showData: Hero2: " + uInfo.getHero2());
        Log.d(TAG, "showData: Hero3: " + uInfo.getHero3());
        Log.d(TAG, "showData: Hero4: " + uInfo.getHero4());
        Log.d(TAG, "showData: Hero5: " + uInfo.getHero5());
        Log.d(TAG, "showData: Hero6: " + uInfo.getHero6());
        Log.d(TAG, "showData: Hero7: " + uInfo.getHero7());
        Log.d(TAG, "showData: Hero8: " + uInfo.getHero8());
        Log.d(TAG, "showData: Hero9: " + uInfo.getHero9());
        Log.d(TAG, "showData: Hero10: " + uInfo.getHero10());
        Log.d(TAG, "showData: Hero11: " + uInfo.getHero11());
        Log.d(TAG, "showData: Hero12: " + uInfo.getHero12());


        ArrayList<String> array = new ArrayList<>();
        array.add(uInfo.getHero1());
        array.add(uInfo.getHero2());
        array.add(uInfo.getHero3());
        array.add(uInfo.getHero4());
        array.add(uInfo.getHero5());
        array.add(uInfo.getHero6());
        array.add(uInfo.getHero7());
        array.add(uInfo.getHero8());
        array.add(uInfo.getHero9());
        array.add(uInfo.getHero10());
        array.add(uInfo.getHero11());
        array.add(uInfo.getHero12());

     /*   ArrayAdapter adapter = new ArrayAdapter(this,android.R.layout.simple_list_item_1,array);
        mListView.setAdapter(adapter);*/

        if (mListView.getAdapter() instanceof CustomListAdapter) {
            ((CustomListAdapter) mListView.getAdapter()).updateList(array);
            mListView.setBackgroundColor(ContextCompat.getColor(mListView.getContext(), R.color.category_colors));
        }
    }

}

@Override
public void onStart() {
    super.onStart();
    mAuth.addAuthStateListener(mAuthListener);
}

@Override
public void onStop() {
    super.onStop();
    if (mAuthListener != null) {
        mAuth.removeAuthStateListener(mAuthListener);
    }
}


/**
 * customizable toast
 *
 * @param message
 */
private void toastMessage(String message) {
    Toast.makeText(this, message, Toast.LENGTH_SHORT).show();
}
}

view_database_layout.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="match_parent"
android:orientation="vertical">

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

 <TextView
    android:id="@+id/tvUserInfo"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="User Information"
    android:textAlignment="center"
    android:textColor="@color/colorPrimaryDark"
    android:textSize="25sp"/>

<ListView
    android:id="@+id/listview"
    android:layout_width="match_parent"
    android:layout_height="match_parent"/>

</LinearLayout>

</LinearLayout>

custom_list.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
<TextView
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:id="@+id/textView"
    android:textSize="20px" android:paddingTop="10dip" android:paddingBottom="10dip"/>
</LinearLayout>

DailyInfo.java

public class DailyInfo {

private String hero1;

private String hero2;
private String hero3;
private String hero4;
private String hero5;
private String hero6;
private String hero7;
private String hero8;
private String hero9;
private String hero10;
private String hero11;
private String hero12;



public DailyInfo(){

}


public String getHero1() {
    return hero1;
}

public void setHero1(String hero1) {
    this.hero1 = hero1;
}


public String getHero2() {
 return hero2;
 }

public void setHero2(String hero2) {
    this.hero2 = hero2;
}

public String getHero3() {
    return hero3;
}

public void setHero3(String hero3) {
    this.hero3 = hero3;
}

public String getHero4() {
    return hero4;
}

public void setHero4(String hero4) {
    this.hero4 = hero4;
}

public String getHero5() {
    return hero5;
}

public void setHero5(String hero5) {
    this.hero5 = hero5;
}

public String getHero6() {
    return hero6;
}

public void setHero6(String hero6) {
    this.hero6 = hero6;
}

public String getHero7() {
    return hero7;
}

public void setHero7(String hero7) {
    this.hero7 = hero7;
}

public String getHero8() {
    return hero8;
}

public void setHero8(String hero8) {
    this.hero8 = hero8;
}

public String getHero9() {
    return hero9;
}

public void setHero9(String hero9) {
    this.hero9 = hero9;
}

public String getHero10() {
    return hero10;
}

public void setHero10(String hero10) {
    this.hero10 = hero10;
}

public String getHero11() {
    return hero11;
}

public void setHero11(String hero11) {
    this.hero11 = hero11;
}

public String getHero12() {
    return hero12;
}

public void setHero12(String hero12) {
    this.hero12 = hero12;
}
}

Answer 1

您在收到ValueEventListener上的回复

后创建了适配器

    CustomListAdapter adapter = new CustomListAdapter(ViewDatabase.this , R.layout.custom_list , mList);
    ListView mListView= findViewById(R.id.listview);
    mListView.setAdapter(adapter);

例如，在ViewDatabase onCreate内设置适配器，并根据该初始状态设置颜色。

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

        mListView = findViewById(R.id.listview);
        CustomListAdapter adapter = new CustomListAdapter(this);
        mListView.setAdapter(adapter);

        //[...]
    }

而且，不是创建适配器，而是更新它：

    private void showData(DataSnapshot dataSnapshot) {

        //[...]

        if (mListView.getAdapter() instanceof CustomListAdapter) {
            ((CustomListAdapter)mListView.getAdapter()).updateList(array);
        }
    }

您也可以将ArrayAdapter替换为BaseAdapter作为扩展类：

    public class CustomListAdapter extends BaseAdapter {

        private static final int HERO_COUNT = 12;
        private Context context;
        private List<String> items;

        public CustomListAdapter(Context context) {
            this.context = context;
            items = new ArrayList<>();
        }

        @Override
        public int getCount() {
            return HERO_COUNT;
        }

        @Override
        public String getItem(int position) {
            if (position >= 0 && position < items.size()) {
                return items.get(position);
            }
            return "";
        }

        @Override
        public long getItemId(int position) {
            return 0;
        }

        @Override
        public View getView(int position, View v, ViewGroup parent) {
            View mView = v;
            if (mView == null) {
                LayoutInflater vi = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
                mView = vi.inflate(R.layout.custom_list, null, false);
            }
            //Bind view content here
            //TODO associate holder to tag
            return mView;
        }

        public void updateList(List<String> updatedItems) {
            items.clear();
            items.addAll(updatedItems);
            notifyDataSetChanged();
        }
    }
}

修改

为了在接收到值时要更改列表上的默认背景颜色，您可以在主布局上设置默认颜色：

<?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="match_parent" android:orientation="vertical"> <LinearLayout android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical"> <TextView android:id="@+id/tvUserInfo" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="User Information" android:textAlignment="center" android:textColor="@color/colorPrimaryDark" android:textSize="25sp"/> <ListView android:id="@+id/listview" android:background="@color/empty_color" android:layout_width="match_parent" android:layout_height="match_parent"/> </LinearLayout> </LinearLayout>

然后在收到值时更改它：

private void showData(DataSnapshot dataSnapshot) { //[...] if (mListView.getAdapter() instanceof CustomListAdapter) { ((CustomListAdapter)mListView.getAdapter()).updateList(array); listView.setBackgroundColor(ContextCompat.getColor(listView.getContext(), R.color.loaded_color)); } }

如果您想要更改行颜色，那么当字符串为空时，您需要在getView上更改行布局。

编辑2 指定了视图更改的位置

Answer 2

您正在修改视图，只有在之前没有创建视图时，在数据可用时，下次不会出现这种情况。所以，根据你的代码（应考虑包括持有人顺便说一句）：

public View getView(int position, View v, ViewGroup parent) {
    View mView = v;
    if (mView == null) {
        LayoutInflater vi = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        mView = vi.inflate(R.layout.custom_list, null, false);
    }
    TextView text = (TextView) mView.findViewById(R.id.textView);
    text.setText(getItem(position));
    if (items.isEmpty()) {
         // Set holder color
    } else {
         text.setTextColor(Color.WHITE);
    }   
    return mView;
}

如何在阅读firebase DB后更改ListView上的颜色和字体

CustomListAdapter.java

ViewDatabase.java

view_database_layout.xml

custom_list.xml

DailyInfo.java

2 个答案: