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private LiveDataViewModel viewModel;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_live_data);
}
@Override
public void onAttachedToWindow() {
super.onAttachedToWindow();
viewModel = ViewModelProviders.of(this).get(LiveDataViewModel.class);
MutableLiveData liveData = viewModel.getLiveData();
liveData.observe(this, new Observer() {
@Override
public void onChanged(@Nullable String s) {
Log.d(“huangxiaoguo”, s);
}
});
}
public void onNormalSetUse(View view) {
viewModel.onNormalSetUse();
}
public void onNormalPostUse(View view) {
viewModel.onNormalPostUse();
}
}
记住是ViewModelProviders不是ViewModelProvider。
setValue:
@MainThread
protected void setValue(T value) {
assertMainThread(“setValue”);
mVersion++;
mData = value;
dispatchingValue(null);
}
postValue:
protected void postValue(T value) {
boolean postTask;
synchronized (mDataLock) {
postTask = mPendingData == NOT_SET;
mPendingData = value;
}
if (!postTask) {
return;
}
ArchTaskExecutor.getInstance().postToMainThread(mPostValueRunnable);
}
private final Runnable mPostValueRunnable = new Runnable() {
@Override
public void run() {
Object newValue;
synchronized (mDataLock) {
newValue = mPendingData;
mPendingData = NOT_SET;
}
//noinspection unchecked
setValue((T) newValue);
}
};
发现postValue其实内部进行了线程转换,准终在调用setValue在主线程执行。
小结:setValue只能在主线程进行调用,postValue可以在子线程进行调用
viewModel不可持有view的引用或者任何持有activity上下文的类的引用,如果需要Application的context的话可以继承AndroidViewModel。
package cn.tsou.google2019io.livedata.viewmodel;
import android.app.Application;
import android.arch.lifecycle.AndroidViewModel;
import android.arch.lifecycle.MutableLiveData;
import android.support.annotation.NonNull;
import android.widget.Toast;
/**
A ViewModel must never reference a view, Lifecycle, or any class that may hold a reference to the activity context.
viewModel不可持有view的引用或者任何持有activity上下文的类的引用
如果需要Application的context的话可以继承AndroidViewModel
Activity重复创建的时候,持有的是同一个viewModel实例
*/
public class LiveDataContextViewModel extends AndroidViewModel {
public LiveDataContextViewModel(@NonNull Application application) {
super(application);
}
private MutableLiveData mLiveData;
public MutableLiveData getLiveData() {
if (mLiveData == null) {
mLiveData = new MutableLiveData<>();
}
return mLiveData;
}
public void onNormalSetUse() {
Toast.makeText(getApplication(), “如果需要Application的context的话可以继承AndroidViewModel”, Toast.LENGTH_LONG).show();
getLiveData().setValue(“hahahhahaha===>set”);
}
/**
当不需要ViewModel时(比如Activity调用finish()方法),
ViewModel会回调onCleared()方法,之后会销毁自己。这一好处也是避免了内存泄漏的情况发生
*/
@Override
protected void onCleared() {
//处理一些操作
super.onCleared();
}
}
小结:getApplication()即是全局的上下文
import android.arch.lifecycle.MutableLiveData;
import android.arch.lifecycle.Observer;
import android.arch.lifecycle.ViewModelProviders;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import cn.tsou.google2019io.R;
import cn.tsou.google2019io.livedata.viewmodel.LiveDataContextViewModel;
import cn.tsou.google2019io.livedata.viewmodel.LiveDataViewModel;
public class LiveDataContextActivity extends AppCompatActivity {
private LiveDataContextViewModel viewModel;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_live_data_context);
}
@Override
public void onAttachedToWindow() {
super.onAttachedToWindow();
viewModel = ViewModelProviders.of(this).get(LiveDataContextViewModel.class);
MutableLiveData liveData = viewModel.getLiveData();
liveData.observe(this, new Observer() {
@Override
public void onChanged(@Nullable String s) {
Log.d(“huangxiaoguo”, s);
}
});
}
public void onNormalSetUse(View view) {
viewModel.onNormalSetUse();
}
}
viewmodel传递数据一般需要自定义Factory
import android.arch.lifecycle.MutableLiveData;
import android.arch.lifecycle.ViewModel;
import android.arch.lifecycle.ViewModelProvider;
import android.util.Log;
public class LiveDataSetDataViewModel extends ViewModel {
private String mKey;
private String mKey1;
public LiveDataSetDataViewModel(String key, String key1) {
this.mKey = key;
this.mKey1 = key1;
}
public static class Factory implements ViewModelProvider.Factory {
private String mKey;
private String mKey1;
public Factory(String key, String key1) {
mKey = key;
mKey1 = key1;
}
@Override
public T create(Class modelClass) {
return (T) new LiveDataSetDataViewModel(mKey, mKey1);
}
}
private MutableLiveData mLiveData;
public MutableLiveData getLiveData() {
if (mLiveData == null) {
mLiveData = new MutableLiveData<>();
}
return mLiveData;
}
public void onNormalSetUse() {
Log.d(“huangxiaoguo”, mKey + “------” + mKey1);
getLiveData().setValue(“hahahhahaha===>set”);
}
@Override
protected void onCleared() {
super.onCleared();
}
}
import android.arch.lifecycle.MutableLiveData;
import android.arch.lifecycle.Observer;
import android.arch.lifecycle.ViewModelProviders;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import cn.tsou.google2019io.R;
import cn.tsou.google2019io.livedata.viewmodel.LiveDataSetDataViewModel;
public class LiveDataSetDataActivity extends AppCompatActivity {
private LiveDataSetDataViewModel viewModel;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_live_data_set_data);
}
@Override
public void onAttachedToWindow() {
super.onAttachedToWindow();
viewModel = ViewModelProviders.of(this, new LiveDataSetDataViewModel.Factory(“传递的参数”,“传递的参数1”)).get(LiveDataSetDataViewModel.class);
MutableLiveData liveData = viewModel.getLiveData();
liveData.observe(this, new Observer() {
@Override
public void onChanged(@Nullable String s) {
Log.d(“huangxiaoguo”, s);
}
});
}
public void onNormalSetUse(View view) {
viewModel.onNormalSetUse();
}
}
自定义LiveData一般都是重写onActive 和onInactive ,这里就拿一篇网上现成的例子来说明(范例来源:gdutxiaoxu的博客)
这里我们以观察网络状态变化为例子讲解
首先我们自定义一个 Class NetworkLiveData,继承 LiveData,重写它的 onActive 方法和 onInactive 方法
在 onActive 方法中,我们注册监听网络变化的广播,即ConnectivityManager.CONNECTIVITY_ACTION。在 onInactive 方法的时候,我们注销广播。
public class NetworkLiveData extends LiveData {
private final Context mContext;
static NetworkLiveData mNetworkLiveData;
private NetworkReceiver mNetworkReceiver;
private final IntentFilter mIntentFilter;
private static final String TAG = “NetworkLiveData”;
public NetworkLiveData(Context context) {
mContext = context.getApplicationContext();
mNetworkReceiver = new NetworkReceiver();
mIntentFilter = new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION);
}
public static NetworkLiveData getInstance(Context context) {
if (mNetworkLiveData == null) {
mNetworkLiveData = new NetworkLiveData(context);
}
return mNetworkLiveData;
}
@Override
protected void onActive() {
super.onActive();
Log.d(TAG, “onActive:”);
mContext.registerReceiver(mNetworkReceiver, mIntentFilter);
}
@Override
protected void onInactive() {
super.onInactive();
Log.d(TAG, "onInactive: ");
mContext.unregisterReceiver(mNetworkReceiver);
}
private static class NetworkReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
ConnectivityManager manager = (ConnectivityManager) context
.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo activeNetwork = manager.getActiveNetworkInfo();
getInstance(context).setValue(activeNetwork);
}
}
}
这样,当我们想监听网络变化的时候,我们只需要调用相应的 observe 方法即可,方便又快捷。
NetworkLiveData.getInstance(this).observe(this, new Observer() {
@Override
public void onChanged(@Nullable NetworkInfo networkInfo) {
Log.d(TAG, “onChanged: networkInfo=” +networkInfo);
}
});
小结:如果想要在数据传递之前对数据进行统一操作,重写setValue方法即可,因为postValue最终调用的还是setValue。
在fragment中livaData的使用和Activity相同
import android.arch.lifecycle.MutableLiveData;
import android.arch.lifecycle.ViewModel;
public class LiveDataFragmentViewModel extends ViewModel {
private MutableLiveData mLiveData;
public MutableLiveData getLiveData() {
if (mLiveData == null) {
mLiveData = new MutableLiveData<>();
}
return mLiveData;
}
public void onNormalSetUse() {
getLiveData().setValue(“LiveData3Fragment===>set”);
}
public void onNormalPostUse() {
new Thread(new Runnable() {
@Override
public void run() {
getLiveData().postValue(“LiveData3Fragment===>post”);
}
}).start();
}
}
package cn.tsou.google2019io.livedata.mylivedata.fragment;
import android.arch.lifecycle.MutableLiveData;
import android.arch.lifecycle.Observer;
import android.arch.lifecycle.ViewModelProviders;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import cn.tsou.google2019io.R;
import cn.tsou.google2019io.livedata.viewmodel.LiveDataFragmentViewModel;
/**
*/
public class LiveData3Fragment extends Fragment implements View.OnClickListener {
private LiveDataFragmentViewModel viewModel;
/**
*/
private Button mBtnNormalSet;
/**
*/
private Button mBtnNormalPost;
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View mView = inflater.inflate(R.layout.fragment_livedata, container, false);
initView(mView);
return mView;
}
@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
viewModel = ViewModelProviders.of(this).get(LiveDataFragmentViewModel.class);
MutableLiveData liveData = viewModel.getLiveData();
liveData.observe(this, new Observer() {
@Override
public void onChanged(@Nullable String s) {
Log.d(“huangxiaoguo”, s);
}
});
}
private void initView(View mView) {
mBtnNormalSet = (Button) mView.findViewById(R.id.btn_normal_set);
mBtnNormalSet.setOnClickListener(this);
mBtnNormalPost = (Button) mView.findViewById(R.id.btn_normal_post);
mBtnNormalPost.setOnClickListener(this);
}
@Override
public void onClick(View v) {
switch (v.getId()) {
default:
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