如何正確添加自定義視圖到活動

Question

我試圖構建一個自定義視圖，但由於某種原因它根本不顯示。

爲了節省讀取兩個構造函數，我調用了不帶attr參數的View構造函數，因爲這些函數應該從Layout文件中提取。任何未從這裏獲取的值都在視圖類本身中設置。

我的觀點類：

package mrl233.campustour.AugmentedReality; 

import android.content.Context; 
import android.content.res.Resources; 
import android.content.res.TypedArray; 
import android.graphics.Canvas; 
import android.graphics.Color; 
import android.graphics.Paint; 
import android.graphics.drawable.Drawable; 
import android.hardware.SensorManager; 
import android.text.TextPaint; 
import android.util.AttributeSet; 
import android.view.View; 
import android.widget.TextView; 

import org.w3c.dom.Text; 

import java.util.ArrayList; 
import java.util.List; 

import mrl233.campustour.R; 

/** 
* TODO: document your custom view class. 
*/ 
public class CameraOverlay extends View { 

    private float mAzimuth; 
    private float mPitch; 
    private float mRoll; 
    private String mTextString; 
    private int mTextColor = Color.RED; 
    private float mTextDimension = 80; 
    private Drawable mTextDrawable; 
    private float mTextSize = 29; 
    private TextPaint mTextPaint; 
    private float mTextHeight = 0; 
    private float mTextWidth; 


    public CameraOverlay(Context context, AttributeSet attrs) { 
     super(context, attrs); 
     TypedArray a = context.getTheme().obtainStyledAttributes(
       attrs, 
       R.styleable.CameraOverlay, 
       0, 0); 

     try { 
      mTextString = a.getString(R.styleable.CameraOverlay_exampleString); 
      mAzimuth = a.getFloat(R.styleable.CameraOverlay_exampleFloat_X, 0); 
      mPitch = a.getFloat(R.styleable.CameraOverlay_exampleFloat_Y, 0); 
      mRoll = a.getFloat(R.styleable.CameraOverlay_exampleFloat_Z, 0); 
     } finally { 
      a.recycle(); 
     } 
     init(); 
    } 
    public CameraOverlay(Context con, float azimuth, float pitch, float roll) { 
     this(con,null); 
     this.mAzimuth = azimuth; 
     this.mPitch = pitch; 
     this.mRoll = roll; 
     TypedArray a = con.getTheme().obtainStyledAttributes(
       null, 
       R.styleable.CameraOverlay, 
       0, 0); 

     try { 
      mTextString = a.getString(R.styleable.CameraOverlay_exampleString); 
      mAzimuth = a.getFloat(R.styleable.CameraOverlay_exampleFloat_X, 0); 
      mPitch = a.getFloat(R.styleable.CameraOverlay_exampleFloat_Y, 0); 
      mRoll = a.getFloat(R.styleable.CameraOverlay_exampleFloat_Z, 0); 

     } finally { 
      a.recycle(); 
     } 
     init(); 

    } 
     @Override 
    public void onDraw(Canvas canvas) { 
      super.onDraw(canvas); 
      invalidate(); 
      int paddingLeft = getPaddingLeft(); 
      int paddingTop = getPaddingTop(); 
      int paddingRight = getPaddingRight(); 
      int paddingBottom = getPaddingBottom(); 

      int contentWidth = getWidth() - paddingLeft - paddingRight; 
      int contentHeight = getHeight() - paddingTop - paddingBottom; 

      canvas.drawText("wsfsefseefsfsef", 
        paddingLeft + (contentWidth - mTextWidth), 
        paddingTop + (contentHeight + mTextHeight) 
        ,mTextPaint); 


    } 

} 

這是我的看法佈局：

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    xmlns:custom="http://schemas.android.com/apk/res-auto" 
    android:id="@+id/overlay" > 

    <mrl233.campustour.AugmentedReality.CameraOverlay 
     android:background="#ccc" 
     android:layout_width="300dp" android:layout_height="300dp" android:paddingLeft="20dp" 
     android:paddingBottom="40dp" custom:exampleDimension="24sp" custom:exampleColor="#33b5e5" 
     custom:exampleString="Hello, CameraOverlay" 
     custom:exampleFloat_X="0.1" 
     custom:exampleFloat_Y="0.5" 
     custom:exampleFloat_Z="1"/> 

</FrameLayout> 

我加入這個觀點到到有它自己的觀點的活動。這是Activity類的onCreate方法，我嘗試添加視圖。

@Override 
    @SuppressWarnings("deprecation") 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.content_augment); 

     preview = (FrameLayout) findViewById(R.id.camera_preview); 
     mPreview = new CameraPreview(this, camera); 
     mCameraOverlay = new CameraOverlay(this, 0, 0, 0); 

     preview.addView(mPreview); 
     preview.addView(mCameraOverlay); 
     preview.bringChildToFront(mCameraOverlay); 

    } 

這個活動課的佈局：

<?xml version="1.0" encoding="utf-8"?> 
    <RelativeLayout  xmlns:android="http://schemas.android.com/apk/res/android" 
     xmlns:tools="http://schemas.android.com/tools" 
     xmlns:app="http://schemas.android.com/apk/res-auto" android:layout_width="match_parent" 
     android:layout_height="match_parent" 
     app:layout_behavior="@string/appbar_scrolling_view_behavior" tools:showIn="@layout/augment" 
     tools:context="mrl233.campustour.Activities.Augment"> 

     <FrameLayout 
      android:id="@+id/camera_preview" 
      android:layout_width="match_parent" 
      android:layout_height="match_parent" 
      android:layout_weight="1"> 

     <!--<SurfaceView--> 
      <!--android:layout_width="match_parent"--> 
      <!--android:layout_height="match_parent"--> 
      <!--android:id="@+id/surfaceView"/>--> 

      <mrl233.campustour.AugmentedReality.CameraOverlay 
       xmlns:android="http://schemas.android.com/apk/res/android" 
       android:layout_width="match_parent" 
       android:layout_height="match_parent" 
       /> 
     </FrameLayout> 

    </RelativeLayout> 

Answer 1

我在這裏看到了兩個問題。你不應該在onDraw方法中調用invalidate（），因爲它會導致視圖重繪自己（無限循環）。其次getWidth（）可能是0。你可能想從onSizeChanged方法得到的畫布寬度

private int width; 
private int height; 

@Override 
protected void onSizeChanged(int w, int h, int oldw, int oldh) { 
    super.onSizeChanged(w, h, oldw, oldh); 
    width = w; 
    height = h; 
} 

@Override 
protected void onDraw(Canvas canvas) { 
    super.onDraw(canvas); 
    ... 
    int contentWidth = width - paddingLeft - paddingRight; 
    ... 
} 

嘗試用硬編碼的大小打造成目前你可能會繪製文本屏幕外或給它的空間太小（它可以幫助你發現問題）。我能想到的 最小customView是：

public class CustomView extends View { 
    private TextPaint paint; 

    public CustomView(Context context) { 
     super(context); 
     paint = new TextPaint(Paint.LINEAR_TEXT_FLAG | Paint.ANTI_ALIAS_FLAG); 
     paint.setColor(Color.RED); 
     paint.setTextSize(20); 
    } 

    @Override 
    protected void onDraw(Canvas canvas) { 
     super.onDraw(canvas); 
     canvas.drawText("Hello", 20, 20, paint); 
    } 
} 

和初始化它：

preview.addView(new CustomView(this)); 

有幾個小問題，但它可能讓你去