我在ListView中有一个Fragment，当我从另一个ListView返回时，我想更新Activity中的数据。我已覆盖onResume()中的Fragment方法，修改Adapter中的数据并在notifyDataSetChanged()上调用Adpater，但不知何故ListView没有更新。我怀疑我的Adapter有问题，但我似乎无法找到错误。
我的Adpater的代码：
class ManualExceptionsListAdapter extends BaseAdapter {
private LayoutInflater mInflater;
private TextView mManualExceptions;
SwitchCompat mSwitch;
TextView name;
final Context context = getActivity();
final SharedPreferences mSharedPreferences = PreferenceManager.getDefaultSharedPreferences(context);
int a;
int ifUse = 0;
ManualExceptionsListAdapter(LayoutInflater inflater) {
mInflater = inflater;
}
@Override
public int getCount() {
return (mPermanentManualException.size()+mContactsExceptionNumber.size());
}
@Override
public Object getItem(int i) {
return null;
}
@Override
public long getItemId(int i) {
return 0;
}
@Override
public int getItemViewType(int position) {
if (position < (mContactsExceptionNumber.size())) {
a = 0;
if(position == (mContactsExceptionNumber.size()-1)){
ifUse = 1;
}
return a;
} else {
a = 1;
return a;
}
}
@Override
public int getViewTypeCount() {
return 2;
}
@Override
public void notifyDataSetChanged() {
super.notifyDataSetChanged();
}
@Override
public View getView(int i, View view, ViewGroup viewGroup) {
final int pos;
if(mContactsExceptionNumber.size()>0) {
pos = i - (mContactsExceptionNumber.size());
}else{
pos = 0;
}
int pos2 = 0;
int type = getItemViewType(i);
if(ifUse == 1){
if(mContactsExceptionNumber.size()>0) {
pos2 = i - (mContactsExceptionNumber.size());
Exceptions.index = pos2;
}
}
View v = view;
if (view == null) {
switch (type) {
case 0:
v = mInflater.inflate(R.layout.contacts_exception_row, null);
name = (TextView) v.findViewById(R.id.contact_name);
name.setText(mContactsExceptionNames.get(i));
break;
case 1:
v = mInflater.inflate(R.layout.manual_exception_row, null);
mManualExceptions = (TextView) v.findViewById(R.id.manual_exception_number);
mSwitch = (SwitchCompat) v.findViewById(R.id.manual_exception_switch);
mManualExceptions.setText(mPermanentManualException.get(pos2));
mSwitch.setTag(i);
try {
if (mManualExceptionList.contains(mPermanentManualException.get(pos2))) {
mSwitch.setChecked(true);
}
} catch (Exception e) {
e.printStackTrace();
}
break;
}
}else{
switch (type) {
case 0:
v = mInflater.inflate(R.layout.contacts_exception_row, null);
name = (TextView) v.findViewById(R.id.contact_name);
name.setText(mContactsExceptionNames.get(i));
break;
case 1:
v = mInflater.inflate(R.layout.manual_exception_row, null);
mManualExceptions = (TextView) v.findViewById(R.id.manual_exception_number);
mSwitch = (SwitchCompat) v.findViewById(R.id.manual_exception_switch);
mManualExceptions.setText(mPermanentManualException.get(pos2));
mSwitch.setTag(i);
try {
if (mManualExceptionList.contains(mPermanentManualException.get(pos2))) {
mSwitch.setChecked(true);
}
} catch (Exception e) {
e.printStackTrace();
}
break;
}
}
try {
mSwitch.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View view, MotionEvent motionEvent) {
isTouched = true;
return false;
}
});
} catch (NullPointerException e) {
e.printStackTrace();
}
try {
mSwitch.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton compoundButton, boolean b) {
if (isTouched) {
if (b) {
if (!mManualExceptionList.contains((mPermanentManualException.get(pos)))) {
mManualExceptionList.add((mPermanentManualException.get(pos)));
}
mSharedPreferences.edit().putString("ManualExceptions", TextUtils.
join(",", mManualExceptionList)).apply();
} else {
try {
mManualExceptionList.remove((mPermanentManualException.get(pos)));
mSharedPreferences.edit().putString("ManualExceptions", TextUtils.
join(",", mManualExceptionList)).apply();
} catch (Exception e) {
e.printStackTrace();
}
}
Log.d("RejectCall", "Permanent " + TextUtils.join(",", mPermanentManualException));
Log.d("RejectCall", TextUtils.join(",", mManualExceptionList));
}
}
});
} catch (NullPointerException e) {
e.printStackTrace();
}
return v;
}
}
答案 0 :(得分：9)
您Adapter实施存在多个问题。对我来说太多了，无法就如何修复它给你建议。我将解释如何有效地实施Adapter，然后您可以将其应用于Adapter。
我只想说你应该最佳地切换到使用新的RecyclerView，它比旧版ListView有许多重大改进。您可以找到RecyclerView文档here和Google搜索指南，了解如何使用它here。
如果要在ListView中显示数据，首先应为ListView中的每个项目创建布局。对于此示例，我将使用此布局：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="12dp">
<CheckBox
android:id="@+id/checkbox"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
</RelativeLayout>
要捆绑我们想要在ListView的每个项目中显示的数据，我们编写一个新类，它只包含私有字段中的数据，getter和setter来获取和设置该数据。这些类通常称为视图模型。像上面这样的布局的视图模型可能如下所示：
public class ExampleViewModel {
// This is the text which will be set to the CheckBox
private String text;
// This boolean will be used to save the checked state of the CheckBox
private boolean checked;
public String getText() {
return text;
}
public void setText(String text) {
this.text = text;
}
public boolean isChecked() {
return checked;
}
public void setChecked(boolean checked) {
this.checked = checked;
}
}
此类视图模型的每个实例都代表ListView中的一个项目。当其中一个项目进入ListView的可见区域时，它必须绑定到View中的ListView（这是我们必须在getView()中实现的Adapter）。只要该项目可见，模型将保持与此View绑定，但只要View退出ListView的可见区域，它就会被回收并绑定到一个刚进入可见区域的不同视图模型。这称为视图回收，它可以最大限度地减少ListView的内存占用，并提高整体滚动性能和流动性。 Views是非常昂贵的对象，尤其是Views和findViewById()充气会导致很多性能损失，主要的观点回收是你只需要少量{{1} }然后可以重复使用，因此您可以避免昂贵的膨胀和Views。
我上面解释的大部分内容都是自动发生的。您作为开发人员必须做的是在findViewById()中膨胀正确的Views，或者如果已有可用的那些，则重复使用它们，然后将正确的视图模型绑定到getView()。我知道，如果你第一次听到这个内容，大部分内容似乎相当复杂和令人困惑，但是一旦我们开始查看代码，它就会变得更加简单和明显。
现在我们将View和视图模型中的视图项布局与其一起使用。我们现在需要做的是编写另一个通常称为视图持有者的类。这些视图持有者本质上是围绕ListView中视图的容器类。每个视图持有者都包含一个与ListView中的项目相关联的View，他们还负责将视图模型的数据绑定到ListView。这里有一个视图持有者可以从上面看到视图模型：
View现在我们差不多完成了。现在唯一缺少的是在public class ExampleViewHolder {
// The reference to the CheckBox is saved so we only have to perform the findViewById() once.
private final CheckBox checkBox;
// A reference to the view model which is currently bound to this view holder
private ExampleViewModel currentModel;
// The View associated with this view holder is passed into the constructor from the Adapter.
public ExampleViewHolder(View view) {
// And here we look for all relevant views
// In our case we just need the CheckBox
this.checkBox = (CheckBox) view.findViewById(R.id.checkbox);
}
public void bind(ExampleViewModel viewModel) {
// Unset the listener in case there was one from a previous view model
this.checkBox.setOnCheckedChangeListener(null);
// Save a reference to the view model which is currently bound to this view holder
this.currentModel = viewModel;
// Bind the data to the CheckBox
this.checkBox.setText(viewModel.getText());
this.checkBox.setChecked(viewModel.isChecked());
// Reset the listener
this.checkBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
currentModel.setChecked(isChecked);
}
});
}
}
：
Adapter这就是你所需要的。这几乎是public class ExampleAdapter extends BaseAdapter {
// Each type of view in the `ListView` gets its own id
// In this example we only have one type of View so we only need one id
private static final int EXAMPLE_VIEW_ID = 0;
// The default view id is just a fallback
private static final int DEFAULT_VIEW_ID = EXAMPLE_VIEW_ID;
private final LayoutInflater inflater;
private List<ExampleViewModel> viewModels;
public ExampleAdapter(Context context, List<ExampleViewModel> viewModels) {
// The view models are initially passed in through the constructor.
// You can pass an empty list into the Adapter if there is not data initially.
this.viewModels = viewModels;
this.inflater = LayoutInflater.from(context);
}
@Override
public int getCount() {
if(viewModels == null) {
return 0;
}
return viewModels.size();
}
@Override
public Object getItem(int position) {
return viewModels.get(position);
}
@Override
public long getItemId(int position) {
final Object model = getItem(position);
// Here we check if the model is an instance of ExampleViewModel and if yes we return its id
if(model instanceof ExampleViewModel) {
return EXAMPLE_VIEW_ID;
}
return DEFAULT_VIEW_ID;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if(getItemId(position) == EXAMPLE_VIEW_ID) {
final ExampleViewModel model = (ExampleViewModel) getItem(position);
final ExampleViewHolder viewHolder;
// If the convertView is null we need to inflate a new view
if(convertView == null) {
final View view = this.inflater.inflate(ExampleViewHolder.LAYOUT, parent, false);
viewHolder = new ExampleViewHolder(view);
// Here we set the viewHolder as tag to the View
// This is done so we can reuse the same view holder later on
// Essentially this is the integral part of the whole view recycling process
view.setTag(viewHolder);
} else {
// If the convertView is not null we can just get the view holder with getTag() from the View
viewHolder = (ExampleViewHolder) convertView.getTag();
}
// And we just need to bind the model to the view holder
viewHolder.bind(model);
}
return convertView;
}
}
的最佳实践实现。如果要处理两种或更多不同类型的视图，则需要为每种类型编写视图模型和视图持有者类。您可以编写一个名为Adapter的接口，它看起来像这样：
ViewModel您的每个视图模型都应该实现此接口。然后，您可以在public interface ViewModel {
}
中使用List<ViewModel>，Adapter可以包含所有不同类型的视图模型。
public class TypeOneViewModel implements ViewModel {
}
public class TypeTwoViewModel implements ViewModel {
}
只要所有视图模型都实现此界面，您就可以执行此操作：
final List<ViewModel> models = new ArrayList<ViewModel>();
models.add(new TypeOneViewModel());
models.add(new TypeTwoViewModel());
...
现在包含多种不同类型的视图模型的List可以传递给Adapter。然后Adapter看起来像这样：
public class ExampleAdapter extends BaseAdapter {
private static final int TYPE_ONE_VIEW_ID = 0;
private static final int TYPE_TWO_VIEW_ID = 1;
private static final int DEFAULT_VIEW_ID = TYPE_ONE_VIEW_ID;
private final LayoutInflater inflater;
private List<ViewModel> viewModels;
public ExampleAdapter(Context context, List<ViewModel> viewModels) {
this.viewModels = viewModels;
this.inflater = LayoutInflater.from(context);
}
@Override
public int getCount() {
if(viewModels == null) {
return 0;
}
return viewModels.size();
}
@Override
public ViewModel getItem(int position) {
return viewModels.get(position);
}
@Override
public long getItemId(int position) {
final ViewModel model = getItem(position);
if(model instanceof TypeOneViewModel) {
return TYPE_ONE_VIEW_ID;
}
if(model instanceof TypeTwoViewModel) {
return TYPE_TWO_VIEW_ID;
}
return DEFAULT_VIEW_ID;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if(getItemId(position) == TYPE_ONE_VIEW_ID) {
final TypeOneViewModel model = (TypeOneViewModel) getItem(position);
final TypeOneViewHolder viewHolder;
if(convertView == null) {
final View view = this.inflater.inflate(TypeOneViewHolder.LAYOUT, parent, false);
viewHolder = new TypeOneViewHolder(view);
view.setTag(viewHolder);
} else {
viewHolder = (TypeOneViewHolder) convertView.getTag();
}
viewHolder.bind(model);
}
if(getItemId(position) == TYPE_TWO_VIEW_ID) {
final TypeTwoViewModel model = (TypeTwoViewModel) getItem(position);
final TypeTwoViewHolder viewHolder;
if(convertView == null) {
final View view = this.inflater.inflate(TypeTwoViewHolder.LAYOUT, parent, false);
viewHolder = new TypeTwoViewHolder(view);
view.setTag(viewHolder);
} else {
viewHolder = (TypeTwoViewHolder) convertView.getTag();
}
viewHolder.bind(model);
}
return convertView;
}
}
您还可以通过编写抽象类来统一视图持有者。这样的抽象类看起来像这样：
public abstract class ViewHolder<T extends ViewModel> {
protected final View itemView;
public ViewHolder(View view) {
this.itemView = view;
}
public abstract void bind(T model);
}
如果您使用此抽象类作为视图持有者的基类，您可以像这样编写它们：
public class TypeOneViewHolder extends ViewHolder<TypeOneViewModel> {
public TypeOneViewHolder(View view) {
super(view);
...
}
public void bind(TypeOneViewModel model) {
...
}
}
虽然这部分并不是真的需要。在ListView中处理多种不同类型的项目时，最重要的部分是所有模型都实现了一个通用接口，因此您可以安全地将它们放在同一个List中。
无论如何，整个事情看起来比你的Adapter更简单，更干净，不是吗？这样，您可以在ListView和显示数据的Views中的数据之间实现完美分离，并且可以更加轻松地维护数据。您可以轻松地在视图持有者中实现动画，而无需关注视图回收，并且许多要求变得更加简单。 RecyclerView将所有这些提升到了新的水平。它的工作原理大致相同，但与ListView相比有几个重大改进，我建议你看看它。
我完全忘记了一件事：您可以使用getter公开内部List视图模型，以便您可以从外部修改视图模型。将此类方法添加到Adapter：
public List<ExampleViewModel> viewmodels() {
return viewModels;
}
public void setViewModels(List<ExampleViewModel> models) {
viewModels = models;
}
然后你可以像这样修改Adapter中的视图模型：
adapter.setViewModels(newData);
...
adapter.viewmodels().add(viewModel);
当您完成修改数据后，您可以通过ListView上的notifyDataSetChanged()来更新Adapter。