得到错误的充气布局

Question

我做了一个应用程序，但在上创建方法时，我呼吁setContentView(R.layout.points)

@Override 
    protected void onCreate(Bundle savedInstanceState) 
    { 
     requestWindowFeature(Window.FEATURE_NO_TITLE); 
     super.onCreate(savedInstanceState); 
     getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, 
       WindowManager.LayoutParams.FLAG_FULLSCREEN); 
     setContentView(R.layout.points); 
     final CanvasView canvas = (CanvasView) findViewById(R.id.signature_canvas); 
     // setContentView(R.layout.activity_main); 


    // addTouchListener(); 

     } 

CanvasView.java

package com.example.android.touchview; 

import android.content.Context; 
import android.graphics.Canvas; 
import android.graphics.Color; 
import android.graphics.Paint; 
import android.util.AttributeSet; 
import android.view.View; 

import java.util.List; 

/** 
* Created by Vikas on 7/26/2016. 
*/ 
public class CanvasView extends View 
{ 

    private Paint mPaint = new Paint(); 


    DbActivity db =new DbActivity(); 
    List mPts=db.getData(); 
    float [] points =new float[mPts.size()]; 

    public CanvasView(Context context,AttributeSet attributeSet) 
    { 

     super(context,attributeSet); 
     // Paint paint = mPaint; 

     //canvas.translate(10, 10); 

     //canvas.drawColor(Color.WHITE); 

     //mPaint.setColor(Color.RED); 
     mPaint.setStrokeWidth(0); 
     mPaint.setAntiAlias(true); 
     mPaint.setColor(Color.BLACK); 
     mPaint.setStrokeWidth(3); 

    } 

    @Override 
    protected void onDraw(Canvas canvas) 
    { 
     super.onDraw(canvas); 
     canvas.drawPoints(points, mPaint); 
    } 


} 

，这是我的xml文件

<?xml version="1.0" encoding="utf-8"?> 
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:id="@+id/points_canvas" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent"> 

    <com.example.android.touchview.CanvasView 
     android:id="@+id/signature_canvas" 
     android:layout_width="match_parent" 
     android:layout_height="match_parent" 
     /> 

</FrameLayout> 

DbActivity.java

package com.example.android.touchview; 

/** 
* Created by Vikas on 7/20/2016. 
*/ 

import android.os.Bundle; 
import android.support.v7.app.AppCompatActivity; 
import android.widget.TextView; 

import java.sql.SQLException; 
import java.util.ArrayList; 

public class DbActivity extends AppCompatActivity { 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_db); 
     TextView tv = (TextView) findViewById(R.id.SQLinfo); 
     DataBase db = new DataBase(this); 
     try { 
      db.open(); 
      ArrayList<Float> data = db.getData(); 
      db.close(); 


      // data.toString(); 
      tv.setText(data.toString()); 
      //Log.d("THE DATA IS ", "+ data.get(i)"); 

     /* for(int i=0;i<data.size();i++) 
      { 
       tv.setText(data.get(i).toString()); 
       Log.d("hi", "data[i]"); 
      }*/ 

     } catch (SQLException e) { 
      e.printStackTrace(); 
     } 
    } 

    public ArrayList<Float> getData() 
    { 
     ArrayList<Float> data= new ArrayList<>(); 
     DataBase db = new DataBase(this); 
     try { 
      db.open(); 
      data = db.getData(); 
      db.close(); 


    } catch (SQLException e) 
     { 
      e.printStackTrace(); 
     } 
     return data; 
    } 
} 

修改Canvas.java

package com.example.android.touchview; 

import android.content.Context; 
import android.graphics.Canvas; 
import android.graphics.Color; 
import android.graphics.Paint; 
import android.util.AttributeSet; 
import android.view.View; 

import java.util.List; 

/** 
* Created by Vikas on 7/26/2016. 
*/ 
public class CanvasView extends View 
{ 

    private Paint mPaint = new Paint(); 
    float[] points ; 




    public CanvasView(Context context,AttributeSet attributeSet) 
    { 

     super(context,attributeSet); 
     DbActivity db =new DbActivity(); 
     List mPts=db.getData(); 
     points =new float[mPts.size()]; 

     // Paint paint = mPaint; 

     //canvas.translate(10, 10); 

     //canvas.drawColor(Color.WHITE); 

     //mPaint.setColor(Color.RED); 

    } 

    @Override 
    protected void onDraw(Canvas canvas) 
    { 
     super.onDraw(canvas); 
     mPaint.setStrokeWidth(0); 
     mPaint.setAntiAlias(true); 
     mPaint.setColor(Color.BLACK); 
     mPaint.setStrokeWidth(3); 

     canvas.drawPoints(points, mPaint); 
    } 


} 

Database.java

package com.example.android.touchview; 

/** 
* Created by Vikas on 7/20/2016. 
*/ 
import android.content.ContentValues; 
import android.content.Context; 
import android.database.Cursor; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteOpenHelper; 
import android.util.Log; 

import java.sql.SQLException; 
import java.util.ArrayList; 


public class DataBase 
{ 
    public static final String KEY_ROWID = "_id"; 
    public static final String KEY_X = "X"; 
    public static final String KEY_Y = "Y"; 

    private static final String DATABASE_NAME = "Details"; 
    private static final String DATABASE_TABLE = "DetailsTable"; 
    private static final int DATABASE_VERSION = 1; 

    private DbHelper ourHelper; 
    private final Context ourContext; 
    private SQLiteDatabase ourDatabase; 



    private static class DbHelper extends SQLiteOpenHelper { 

     public DbHelper(Context context) { 
      super(context, DATABASE_NAME, null, DATABASE_VERSION); 
      // TODO Auto-generated constructor stub 
     } 

     @Override 
     public void onCreate(SQLiteDatabase db) { 
      db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE); 
      db.execSQL("CREATE TABLE " + DATABASE_TABLE + " (" + KEY_ROWID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + 
        KEY_X + " TEXT, " + KEY_Y + " TEXT);"); 
     } 

     @Override 
     public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
      db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE); 
      onCreate(db); 
     } 
    } 

    public DataBase(Context c) { 
     ourContext = c; 
    } 

    public DataBase open() throws SQLException { 
     ourHelper = new DbHelper(ourContext); 
     ourDatabase = ourHelper.getWritableDatabase(); 
     return this; 
    } 

    public void close() { 
     ourHelper.close(); 
    } 

    public long createEntry(String x, String y) { 
     ContentValues cv = new ContentValues(); 
     cv.put(KEY_X, x); 
     cv.put(KEY_Y, y); 
     return ourDatabase.insert(DATABASE_TABLE, null, cv); 
    } 

    public ArrayList<Float> getData() { 
     ourDatabase = ourHelper.getReadableDatabase(); 
     Point p = new Point(); 
     ArrayList<Float> dataPoints = new ArrayList<>(); 
     String[] col = new String[]{KEY_ROWID, KEY_X, KEY_Y}; 
     Cursor c = ourDatabase.query(DATABASE_TABLE, col, null, null, null, null, null); 
     float[] array = new float[c.getCount()]; 
     float[] array1 = new float[c.getCount()]; 
     int i = 0; 
     if (c.moveToFirst()) 
     { 
      do { 
       float x = c.getFloat(c.getColumnIndex("X")); 
       p.setX(x); 
       dataPoints.add(p.getX()); 

       float y = c.getFloat(c.getColumnIndex("Y")); 
       p.setY(y); 
       dataPoints.add(p.getY()); 
       array[i] = x; 
       array1[i] = y; 
       i++; 
      } while (c.moveToNext()); 
     } 


     Log.d("hi", "getData() called"); 
     return dataPoints; 
    } 
} 

我收到此错误

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.touchview/com.example.android.touchview.MainActivity}: android.view.InflateException: Binary XML file line #7: Error inflating class com.example.android.touchview.CanvasView 

Answer 1

似乎以下行导致错误：

DbActivity db =new DbActivity(); 
List mPts=db.getData(); 
float [] points =new float[mPts.size()]; 

首先，将所有初始化移动到构造函数方法中，并避免这种初始化方式。其次，你不应该实例化一个活动。

例如，建议将所有数据库级逻辑移至名为DbHelper的类，并将其用于方法范围。像这样的东西看起来很好：

DbHelper db; 
List mPts; 
float [] points; 
public CanvasView(Context context,AttributeSet attributeSet) 
{ 
    super(context,attributeSet); 

    db = new DbHelper(...); 
    mPts = new ArrayList<>(); 
    points = new float[...]; 
    ... 
}