[英]setContentView crash when activity_main -> custom
我知道有很多关于使用setContentView崩溃的问题,但是我还没有发现任何像我这样基本的问题。
这基本上是我使用Android Studio的第一天。 目前,我正在关注Paulo Dichone在Udemy上的Android课程。 他要我们做的第一件事就是将开始的布局更改为我们自己做的布局。 即使更改少于一行,也会导致我的仿真程序在Genymotion中崩溃。
这是MainActivity.java的代码。 我从原始文件更改的唯一内容(有效)是activity_main作为setContentView的参数(在onCreate的第二行中),我将其更改为mylayout。
package welcomeandroid.myandroid.com.welcomeandroid;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.mylayout);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
我的自定义布局“ mylayout”的XML代码如下:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="Please work"
android:id="@+id/textView2"
android:layout_gravity="center_horizontal" />
运行该程序的logcat消息如下:
11-12 23:28:17.584 2244-2244/? I/art: Late-enabling -Xcheck:jni
11-12 23:28:18.026 2244-2244/welcomeandroid.myandroid.com.welcomeandroid D/AndroidRuntime: Shutting down VM
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: FATAL EXCEPTION: main
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: Process: welcomeandroid.myandroid.com.welcomeandroid, PID: 2244
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{welcomeandroid.myandroid.com.welcomeandroid/welcomeandroid.myandroid.com.welcomeandroid.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.CharSequence android.support.v7.widget.Toolbar.getTitle()' on a null object reference
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at android.app.ActivityThread.access$800(ActivityThread.java:151)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:102)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at android.os.Looper.loop(Looper.java:135)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5254)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:372)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.CharSequence android.support.v7.widget.Toolbar.getTitle()' on a null object reference
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at android.support.v7.internal.widget.ToolbarWidgetWrapper.<init>(ToolbarWidgetWrapper.java:100)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at android.support.v7.internal.widget.ToolbarWidgetWrapper.<init>(ToolbarWidgetWrapper.java:93)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at android.support.v7.internal.app.ToolbarActionBar.<init>(ToolbarActionBar.java:78)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at android.support.v7.app.AppCompatDelegateImplV7.setSupportActionBar(AppCompatDelegateImplV7.java:206)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at android.support.v7.app.AppCompatActivity.setSupportActionBar(AppCompatActivity.java:99)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at welcomeandroid.myandroid.com.welcomeandroid.MainActivity.onCreate(MainActivity.java:19)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at android.app.Activity.performCreate(Activity.java:5990)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at android.app.ActivityThread.access$800(ActivityThread.java:151)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:102)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at android.os.Looper.loop(Looper.java:135)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5254)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:372)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
11-12 23:28:18.028 2244-2244/welcomeandroid.myandroid.com.welcomeandroid E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
11-12 23:28:22.531 2244-2244/welcomeandroid.myandroid.com.welcomeandroid I/Process: Sending signal. PID: 2244 SIG: 9
我真的很感谢您的帮助。 遇到这样的麻烦有点令人沮丧,因为他们仅按照指导员指示的方式更改了少量代码。
您必须从代码中删除以下几行:
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
因为您的布局中没有工具栏和FloatingActionButton。
就像迈克说的那样,您的布局没有工具栏或FloatingActionButton。 试试这个XML可能对您有帮助
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.design.widget.AppBarLayout
android:id="@+id/appbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="Please work"
android:id="@+id/textView2"
android:layout_gravity="center_horizontal" />
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
/>
</android.support.design.widget.AppBarLayout>
<android.support.design.widget.FloatingActionButton
android:id="@+id/fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="right|bottom"
android:layout_marginBottom="@dimen/activity_vertical_margin"
android:layout_marginRight="@dimen/activity_horizontal_margin"
android:src="@drawable/ic_refresh_white_36dp"
app:borderWidth="0dp" />
</LinearLayout>
祝好运
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