使用 AppCompat v22.1.0 时如何在 super.onCreate 之前设置 ContentView？

Question

嘿，我刚刚将我的应用程序升级到 AppCompat v22.1.0 并遇到了这个异常

Caused by: java.lang.IllegalArgumentException: AppCompat does not support the current theme features
        at android.support.v7.app.AppCompatDelegateImplV7.ensureSubDecor(AppCompatDelegateImplV7.java:360) 
        at android.support.v7.app.AppCompatDelegateImplV7.setContentView(AppCompatDelegateImplV7.java:246) 
        at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:106)

我找到了解决方案。这里

问题仍然没有解决，因为我在 super.onCreate 之后调用了 setContentView，在 ConnectionWifiEditActivity Class.

当我更改它时它抛出 NullPointerException 我该如何解决这个问题？

Caused by: java.lang.NullPointerException
            at Client.Activity.connection.ConnectionEditActivity.onResume(ConnectionEditActivity.java:46)
            at Client.Activity.connection.ConnectionWifiEditActivity.onResume(ConnectionWifiEditActivity.java:81)

ConnectionWifiEditActivity

public class ConnectionWifiEditActivity extends ConnectionEditActivity implements OnClickListener
{
    private ConnectionWifi connection;
    private EditText host;
    private EditText port;
    Button scan;
    ListView lv;
    private Toolbar mToolbar;

    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        this.setContentView(R.layout.connectionwifiedit);
        lv = (ListView) findViewById(android.R.id.list);
        this.connection = (ConnectionWifi) connectionParam;
        mToolbar = (Toolbar) findViewById(R.id.toolbar_actionbar);
        setSupportActionBar(mToolbar);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        this.host = (EditText) this.findViewById(R.id.host);
        this.port = (EditText) this.findViewById(R.id.port);
        SnackbarManager.show(
                Snackbar.with(getApplicationContext()) // context
                        .type(SnackbarType.MULTI_LINE) // Set is as a multi-line snackbar
                        .text(R.string.tip) // text to be displayed
                        .duration(Snackbar.SnackbarDuration.LENGTH_INDEFINITE)
                , this);
    }

    public void Save(View v){
        this.finish();
    }


    @Override
    public void onClick(View v)
    {

    }

    protected void onResume()
    {
        super.onResume();
        this.host.setText(this.connection.getHost());
        this.port.setText(Integer.toString(this.connection.getPort()));
    }

    protected void onPause()
    {
        super.onPause();

        this.connection.setHost(this.host.getText().toString());
        this.connection.setPort(Integer.parseInt(this.port.getText().toString()));
    }}

ConnectionEditActivity

public static Connection connectionParam;

    private Connection connection;

    private EditText name;
    private EditText password;

    public class ConnectionEditActivity extends AppCompatActivity implements OnClickListener
    {
        public static Connection connectionParam;

        private Connection connection;

        private Button save;

        private EditText name;
        private EditText password;

        protected void onCreate(Bundle savedInstanceState)
        {
            super.onCreate(savedInstanceState);
            this.connection = connectionParam;
            this.name = (EditText) this.findViewById(R.id.name);
            this.password = (EditText) this.findViewById(R.id.password);

        }

        protected void onResume()
        {
            super.onResume();
            this.name.setText(this.connection.getName());
            this.password.setText(this.connection.getPassword());
        }

        protected void onPause()
        {
            super.onPause();
            this.connection.setName(this.name.getText().toString());
            this.connection.setPassword(this.password.getText().toString());
        }

        public void onClick(View v)
        {
            if (v == this.save)
            {
                this.finish();
            }
        }
    }

连接

public abstract class Connection implements Comparable<Connection>, Serializable
{
    private static final long serialVersionUID = 1L;

    public static final int TYPE_COUNT = 2;

    public static final int WIFI = 0;
    public static final int BLUETOOTH = 1;

    private String name;
    private String password;

    public Connection()
    {
        this.name = "";
        this.password = RemoteItConnection.DEFAULT_PASSWORD;
    }

    public static Connection load(SharedPreferences preferences, ConnectionList list, int position)
    {
        Connection connection = null;
        int type = preferences.getInt("connection_" + position + "_type", -1);

        switch (type)
        {
            case WIFI:
                connection = ConnectionWifi.load(preferences, position);
                break;
            case BLUETOOTH:
                connection = ConnectionBluetooth.load(preferences, position);
                break;
        }

        connection.name = preferences.getString("connection_" + position + "_name", null);

        connection.password = preferences.getString("connection_" + position + "_password", null);

        return connection;
    }

    public void save(Editor editor, int position)
    {
        editor.putString("connection_" + position + "_name", this.name);

        editor.putString("connection_" + position + "_password", this.password);
    }

    public abstract RemoteItConnection connect(RemoteIt application) throws IOException;

    public abstract void edit(Context context);

    protected void edit(Context context, Intent intent)
    {
        ConnectionEditActivity.connectionParam = this;
        context.startActivity(intent);
    }

    public String getName()
    {
        return name;
    }

    public void setName(String name)
    {
        this.name = name;
    }

    public String getPassword()
    {
        return password;
    }

    public void setPassword(String password)
    {
        this.password = password;
    }

    public int compareTo(Connection c)
    {
        return this.name.compareTo(c.name);
    }
}

Answer 1

只需将此添加到您的样式中（两者都需要）

<item name="windowActionBar">false</item>
<item name="windowNoTitle">true</item>

在 ConnectionEditActivity 中，您在调用 setContentView 之前调用 findViewById，它将始终 return null。所以你的观点将永远是空的。

this.connection = connectionParam;
this.name = (EditText) this.findViewById(R.id.name);
this.password = (EditText) this.findViewById(R.id.password);

Answer 2

既然要在super方法中获取一些ui元素，就得想办法在superclass中定义布局。这是因为您正在获得其他答案中所述的 NPE。

你可以在supersetContentView()中使用class，使用一个方法来return布局来使用。

这样你就可以在子class中重写布局，重写方法

例如，您可以使用 setContentView(getLayoutId()):

public class ConnectionEditActivity extends AppCompatActivity {

    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);

        setContentView(getLayoutId());  //pay attention here...

        this.connection = connectionParam;
        this.name = (EditText) this.findViewById(R.id.name);
        this.password = (EditText) this.findViewById(R.id.password);
    }

    protected int getLayoutId(){
       //....
    }

}

你可以在其他 activity 中覆盖它，在那里你可以避免 setContentView 方法。

public class ConnectionWifiEditActivity extends ConnectionEditActivity{

   @Override
   protected int getLayoutId(){
       return R.layout.connectionwifiedit;
   }

    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        //setContentView();   //comment this line
        //..
    }

}

Answer 3

小技巧是在您的父级中使用 override fun onPostCreate(savedInstanceState: Bundle?) 方法来查找视图

使用 AppCompat v22.1.0 时如何在 super.onCreate 之前设置 ContentView？

How to setContentView before super.onCreate while using AppCompat v22.1.0?

android

android-appcompat

setcontentview

appcompatactivity