Android Studio； 正在启动至USB设备（电话），已安装但无法打开

Question

我的应用程序构建成功并说成功，但是当我在手机上打开应用程序时，它退出并没有启动。 我的清单文件有问题吗？

错误：java.lang.RuntimeException：无法启动活动ComponentInfo {com.example.terik.thirdattempt / com.example.terik.thirdattempt.MainActivity}：android.view.InflateException：二进制XML文件第23行：膨胀类android的错误.widget.Button

这是XML

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.terik.thirdattempt" >
<uses-sdk android:minSdkVersion="8" />
<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name=".MainActivity"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

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

</manifest>

这是我踢球和傻笑的布局。

<TextView android:layout_width="500dp"
    android:layout_height="200dp"
    android:text="0"
    android:textSize="72pt"
    android:id="@+id/textView"
    android:layout_alignParentTop="true"
    android:layout_alignLeft="@+id/Button1"
    android:layout_alignStart="@+id/Button1"
    android:layout_marginLeft="41dp"
    android:layout_marginStart="71dp"
    android:layout_alignRight="@+id/Button1"
    android:layout_alignEnd="@+id/Button1"></TextView>

 <Button
    android:layout_width="200dp"
    android:layout_height="200dp"
    android:id="@+id/Button1"
    android:background="@drawable/custom_button"
    android:adjustViewBounds="false"
    android:layout_alignParentBottom="true"
    android:layout_centerHorizontal="true"
    android:layout_marginBottom="51dp" />


</RelativeLayout>

我猜我的MainActivity.java文件

package com.example.terik.thirdattempt;

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.TextView;


public class MainActivity extends ActionBarActivity {
int number = 0;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    textView=(TextView)findViewById(R.id.textView);
}


@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);
}

public void addOne(View view){
    number = number +1;
    textView.setText(number);
}

}

Answer 1

空指针异常是因为您在setcontent视图之前声明了textview。 这应该可以解决（但我不明白addOne是什么方法，所以我不理会它）：

int number = 0;
TextView textView;
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    textView = (TextView)findViewById(R.id.textView);
}


@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);
}
public void addOne(View view){
    number = number +1;
    textView.setText(number);
}

Answer 2

您可以在onCreate函数中的setContentView（R.layout.activity_main）之后初始化UI。

因此，当您启动设备时，您的应用程序崩溃了。您应该在onCreate函数之后初始化TextView，如下所示：

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    textView = (TextView)findViewById(R.id.textView);
}