java - Splash Activity 和应用程序关闭后，运行时主 Activity 不会出现

Question

我的代码中的所有内容在 .java 和 .xml 文件中看起来都很好(根据软件)，因为每次我单击模拟器中的应用程序图标时，我都没有错误，它会显示启动屏幕，然后显示应用程序退出而不显示我的主要 Activity 。到目前为止，这是我的代码:

SplashActivity.java

public class SplashActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    //hide title bar of activity
    getWindow().requestFeature(Window.FEATURE_NO_TITLE);
    //Making activity full screen
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
    setContentView(R.layout.activity_splash);

    int t =3000; //time for spash screen 3000 means 3sec
    new Handler().postDelayed(new Runnable() {
        @Override
        public void run() {

            startActivity(new Intent(SplashActivity.this, MainActivity.class));
        }
    },t);
}

}

SplashActivity.xml

<ImageView
    android:layout_width="250dp"
    android:layout_height="250dp"
    android:src="@drawable/icon"
    android:text="Hello World!"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

MainActivity.java:

public class MainActivity extends AppCompatActivity
    {

String webAdress ="https://www.google.com/";
WebView webView;
FrameLayout frameLayout;
ProgressBar progressBar;

@Override
protected void onCreate(Bundle savedInstanceState) {


    super.onCreate(savedInstanceState);
    webView = (WebView) findViewById(R.id.webView);
    frameLayout = (FrameLayout) findViewById(R.id.frameLayout);
    progressBar = (ProgressBar) findViewById(R.id.progressBar);

    webView.setWebViewClient(new HelpClient());
    webView.setWebChromeClient(new WebChromeClient() {
        @Override
        public void onProgressChanged(WebView view, int newProgress) {
            frameLayout.setVisibility(View.VISIBLE);
            progressBar.setProgress(newProgress);
            setTitle("Loading...");  //when url is loading set this on actionbar
            if (newProgress == 100) {
                frameLayout.setVisibility(View.GONE); // Hide progress bar when page is loaded
                setTitle(view.getTitle()); //get amd set title of opend page
            }
            super.onProgressChanged(view, newProgress);
        }
    });

    webView.getSettings().setJavaScriptEnabled(true); //enable javaScript

    //check internet connection
    if (haveNetworkConnection()) {
        webView.loadUrl(webAdress);
    } else {

        Toast.makeText(this, "No internet Connection", Toast.LENGTH_SHORT).show();
    }
    progressBar.setProgress(0);

}




private class HelpClient extends WebViewClient {

    @Override
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
        view.loadUrl(url);
        frameLayout.setVisibility(View.VISIBLE);
        return true;
    }
}

private boolean haveNetworkConnection(){
    boolean haveConnectedWifi = false;
    boolean haveConnectedMobile = false;

    ConnectivityManager cm = (ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo[] networkInfos = cm.getAllNetworkInfo();

    for(NetworkInfo ni : networkInfos){
        if(ni.getTypeName().equalsIgnoreCase("WIFI"))
            if (ni.isConnected())
                haveConnectedWifi = true;

        if(ni.getTypeName().equalsIgnoreCase("MOBILE"))
            if (ni.isConnected())
                haveConnectedMobile = true;


    }
    return haveConnectedWifi || haveConnectedMobile;
}

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    //check if the event was the back button and if there's history
    if ((keyCode==KeyEvent.KEYCODE_BACK) && webView.canGoBack()){
        webView.goBack();
        return true;
    }

    //if it was the back or there is no web page history, bubble up to the default system behaviour
    return super.onKeyDown(keyCode, event);
}

}

MainActivity.xml:

<!--Progressbar-->
<FrameLayout
    android:id="@+id/frameLayout"
    android:layout_width="match_parent"
    android:layout_height="3dip"
    android:background="@android:color/transparent">
    <ProgressBar
        android:id="@+id/progressBar"
        android:layout_width="match_parent"
        style="?android:attr/progressBarStyleHorizontal"
        android:layout_height="7dp"
        android:layout_gravity="top"
        android:layout_marginTop="-3dp"
        android:progressDrawable="@drawable/custom_progress"
        android:background="@android:color/transparent"
        android:progress="20"/>
</FrameLayout>

<!--WebView-->
<WebView
    android:id="@+id/webView"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_weight="1">
</WebView>

这是我的 list .xml:

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<!--internet permision-->
<uses-permission android:name="android.permission.INTERNET"/>

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".SplashActivity"
        android:theme="@style/Theme.AppCompat.Light.NoActionBar">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity
        android:name=".MainActivity">

    </activity>

</application>

如有任何提示，我们将不胜感激，谢谢!

Answer 1

问题出在MainActivity的onCreate方法中，您没有提供任何UI(xml布局文件)，导致应用程序找不到要初始化的 View 元素、设置监听器等。我猜你可以在应用程序关闭时在 logcat 中找到异常。

解决方案:为MainActivity提供布局xml文件

public class MainActivity extends AppCompatActivity {

    String webAdress ="https://www.google.com/";
    WebView webView;
    FrameLayout frameLayout;
    ProgressBar progressBar;

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

        webView = (WebView) findViewById(R.id.webView);
        ...
    }
}