Question

我刚开始学习Android，我遇到了问题。对于新的Android Studio，我为每个活动都有两个XML个文件，所以不要得到NullPointerException我必须稍微更改一下findViewById。但现在我无法更改TextView中的文字。

代码：

public class MainActivity extends AppCompatActivity {


    LinearLayout layoutMain;
    TextView tvText;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        layoutMain = (LinearLayout) View.inflate(this, R.layout.content_main, null);
        tvText = (TextView) layoutMain.findViewById(R.id.tvText);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();

        switch (id) {
            case R.id.action_settings1:
                  tvText.setText("one");
                Log.d("USER","one");
                break;
            case R.id.action_settings2:
                tvText.setText("two");
                Log.d("USER", "two");
                break;
        }
        return super.onOptionsItemSelected(item);
    }

}

XML文件：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="com.example.myapp6.MainActivity"
    tools:showIn="@layout/activity_main">


    <TextView
        android:id="@+id/tvText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!" />
</LinearLayout>

<android.support.design.widget.AppBarLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:theme="@style/AppTheme.AppBarOverlay">

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        app:popupTheme="@style/AppTheme.PopupOverlay" />

</android.support.design.widget.AppBarLayout>

<include layout="@layout/content_main" />

Answer 1

更改

tvText = (TextView) layoutMain.findViewById(R.id.tvText);

到

tvText = (TextView) findViewById(R.id.tvText);

您收到TextView的错误引用。

Answer 2

public class MainActivity extends AppCompatActivity {

View includedView;
TextView tvText;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    includedView = (View) findViewById(R.id.includedView);
    tvText = (TextView) includedView.findViewById(R.id.tvText);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    int id = item.getItemId();

    switch (id) {
        case R.id.action_settings1:
              tvText.setText("one");
            Log.d("USER","one");
            break;
        case R.id.action_settings2:
            tvText.setText("two");
            Log.d("USER", "two");
            break;
    }
    return super.onOptionsItemSelected(item);
}

}

xml文件中也有一点改变

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:context="com.example.myapp6.MainActivity"
tools:showIn="@layout/activity_main">


<TextView
    android:id="@+id/tvText"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Hello World!" />
</LinearLayout>

和第二个xml

<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/AppTheme.AppBarOverlay">

<android.support.v7.widget.Toolbar
    android:id="@+id/toolbar"
    android:layout_width="match_parent"
    android:layout_height="?attr/actionBarSize"
    android:background="?attr/colorPrimary"
    app:popupTheme="@style/AppTheme.PopupOverlay" />

</android.support.design.widget.AppBarLayout>

<include layout="@layout/content_main" 
android:id="@+id/includedView"/>

Answer 3

将content_main布局复制并粘贴到activity_main xml中，然后删除content_main xml文件。

然后将onCreate()中的代码更改为：

@Override 
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        layoutMain = (LinearLayout) findViewById(R.id.content_main);
        //content_main should be the id of the layout you copied!

        tvText = (TextView) findViewById(R.id.tvText);
    }

Android - 无法在TextView中更改文本

3 个答案: