如何使用onDraw/drawRect从editText从mainActivity生成一个矩形
如何使用onDraw/drawRect从editText从mainActivity生成一个矩形
提问于 2019-06-13 20:49:42
基本上，我试图从用户那里收集房间的大小.(例如20x20大小的房间)。使用在mainActivity上收集的这些维度，将数据发送到结果活动，并使用onDraw/on测量创建一个简单的框。
简而言之，我想从用户那里收集mainActivity中的框的大小。然后在结果活动中显示框的完整图像。
我已经用数据完成了从一个活动到另一个活动的传递意图。它使用收集的数据绘制一个形状，我有困难。
public class MainActivity extends AppCompatActivity {
//variables
Button btnCalculate, btnReset;
Spinner spinSpeaker;
EditText editLength, editWidth, editHeight;
String t1,t2,t3;
int numLength, numWidth, numHeight, numResult=0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//connecting variables to GUI elements
btnCalculate= findViewById(R.id.btnCalculate);
btnReset = findViewById(R.id.btnReset2);
spinSpeaker = findViewById(R.id.spinSpeaker);
editLength= findViewById(R.id.editLength);
editWidth = findViewById(R.id.editWidth);
editHeight = findViewById(R.id.editHeight);
//adding function to the calculate button
btnCalculate.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//parsing text to integers
t1=editLength.getText().toString();
t2=editWidth.getText().toString();
t3=editHeight.getText().toString();
if (t3.equals("")) {
editHeight.setText("11");
}else if (t2.equals("")) {
editWidth.setText("11");
}else if (t1.equals("")) {
editLength.setText("11");
}else{
numLength = Integer.parseInt(t1);
numWidth = Integer.parseInt(t2);
numHeight = Integer.parseInt(t3);
}
//alert to contact Pro design
if ((numLength>=999)||(numWidth>=999)||(numHeight>=20)) {
Toast.makeText(MainActivity.this, R.string.contactPro,
Toast.LENGTH_LONG).show();
}else {
//calculating volume
numResult = numHeight * numWidth * numLength;
//sending data to other activities
Intent intent = new Intent(MainActivity.this, Result.class);
intent.putExtra("varHeight", numHeight);
intent.putExtra("varWidth", numWidth);
intent.putExtra("varLength", numLength);
intent.putExtra("varResult", numResult);
startActivity(intent);
}
}
});
}//Result activity
public class Result extends AppCompatActivity {
TextView tim;
MyCanvas mycanvas;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mycanvas = new MyCanvas(this);
setContentView(R.layout.activity_result);
setContentView(Jim);
//Pulling variables from main activity
Intent variables = getIntent();
//int length = variables.getIntExtra("varLength",0);
//int width =variables.getIntExtra("varWidth",0);
int totalResult = variables.getIntExtra("varResult",0);
//showing total
String result = String.valueOf(totalResult);
tim = findViewById(R.id.txtResult);
tim.setText(result);
//Calling the reset button method
configureResetBtn();
}
public void configureResetBtn(){
Button btnReset=findViewById(R.id.btnReset2);
btnReset.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//startActivity(new Intent(Result.this, MainActivity.class));
finish();
}
});
}
}//MyCanvas activity
public class MyCanvas extends AppCompatActivity {
public MyCanvas(Result result) {
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Intent variables = getIntent();
final int length = variables.getIntExtra("varLength", 0);
final int width = variables.getIntExtra("varWidth", 0);
class Jim extends View {
Paint paint = new Paint();
Rect rect = new Rect();
public Jim(Context context) {
super(context);
}
@Override
protected void onDraw(android.graphics.Canvas canvas) {
super.onDraw(canvas);
paint.setStrokeWidth(3);
canvas.drawRect(0, 0, canvas.getWidth(), canvas.getHeight(), paint);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
setMeasuredDimension(length,width);
}
}
}
}预期的结果是显示一个框，它是基于用户的维度(例如，20x20)。但是，我得到了这个错误：
android.widget.Button.setOnClickListener(android.view.View$OnClickListener)‘：尝试在空对象引用上调用虚拟方法的void java.lang.NullPointerException
但是当我删除试图绘制框的代码时，我的按钮就能工作了。
回答 1
Stack Overflow用户
回答已采纳
发布于 2019-06-14 03:28:01
不要在ResultActivity中设置两次内容视图，而是在R.layout.activity_result中使用SurfaceView
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<SurfaceView
android:id="@+id/surface_view"
android:layout_width="match_parent"
android:layout_height="match_parent" />
//....
</FrameLayout>在ResultActivity中
SurfaceView surfaceView = findViewById(R.id.surface_view);
surfaceView.getHolder().addCallback(new Callback() {
@Override
public void surfaceCreated(SurfaceHolder holder) {
Canvas canvas = holder.lockCanvas();
// draw
Paint paint = new Paint();
paint.setStrokeWidth(3);
canvas.drawRect(0, 0, canvas.getWidth(), canvas.getHeight(), paint);
holder.unlockCanvasAndPost(canvas);
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
}
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
}
});页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/56588381
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